[PATCH v5 0/7] DAX fsync/msync support

[PATCH v5 0/7] DAX fsync/msync support

[Ross Zwisler]

Changes from v4:
 - Explicity prevent shadow entries from being added to radix trees for DAX
   mappings in patch 2.  The only shadow entries that would be generated
   for DAX radix trees would be to track zero page mappings that were
   created for holes.  These pages would receive minimal benefit from
   having shadow entries, and the choice to have only one type of
   exceptional entry in a given radix tree makes the logic simpler both in
   clear_exceptional_entry() and in the rest of DAX.  (Jan)

 - Added Reviewed-by from Jan to patch 3.

This series is built upon ext4/master.  A working tree with this series
applied can be found here:

https://git.kernel.org/cgit/linux/kernel/git/zwisler/linux.git/log/?h=fsync_v5

Ross Zwisler (7):
  pmem: add wb_cache_pmem() to the PMEM API
  dax: support dirty DAX entries in radix tree
  mm: add find_get_entries_tag()
  dax: add support for fsync/sync
  ext2: call dax_pfn_mkwrite() for DAX fsync/msync
  ext4: call dax_pfn_mkwrite() for DAX fsync/msync
  xfs: call dax_pfn_mkwrite() for DAX fsync/msync

 arch/x86/include/asm/pmem.h |  11 +--
 fs/block_dev.c              |   3 +-
 fs/dax.c                    | 159 ++++++++++++++++++++++++++++++++++++++++++--
 fs/ext2/file.c              |   4 +-
 fs/ext4/file.c              |   4 +-
 fs/inode.c                  |   1 +
 fs/xfs/xfs_file.c           |   7 +-
 include/linux/dax.h         |   7 ++
 include/linux/fs.h          |   1 +
 include/linux/pagemap.h     |   3 +
 include/linux/pmem.h        |  22 +++++-
 include/linux/radix-tree.h  |   9 +++
 mm/filemap.c                |  84 ++++++++++++++++++++++-
 mm/truncate.c               |  64 ++++++++++--------
 mm/vmscan.c                 |   9 ++-
 15 files changed, 339 insertions(+), 49 deletions(-)

-- 
2.5.0

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[PATCH v5 0/7] DAX fsync/msync support

[Ross Zwisler]

Changes from v4:
 - Explicity prevent shadow entries from being added to radix trees for DAX
   mappings in patch 2.  The only shadow entries that would be generated
   for DAX radix trees would be to track zero page mappings that were
   created for holes.  These pages would receive minimal benefit from
   having shadow entries, and the choice to have only one type of
   exceptional entry in a given radix tree makes the logic simpler both in
   clear_exceptional_entry() and in the rest of DAX.  (Jan)

 - Added Reviewed-by from Jan to patch 3.

This series is built upon ext4/master.  A working tree with this series
applied can be found here:

https://git.kernel.org/cgit/linux/kernel/git/zwisler/linux.git/log/?h=fsync_v5

Ross Zwisler (7):
  pmem: add wb_cache_pmem() to the PMEM API
  dax: support dirty DAX entries in radix tree
  mm: add find_get_entries_tag()
  dax: add support for fsync/sync
  ext2: call dax_pfn_mkwrite() for DAX fsync/msync
  ext4: call dax_pfn_mkwrite() for DAX fsync/msync
  xfs: call dax_pfn_mkwrite() for DAX fsync/msync

 arch/x86/include/asm/pmem.h |  11 +--
 fs/block_dev.c              |   3 +-
 fs/dax.c                    | 159 ++++++++++++++++++++++++++++++++++++++++++--
 fs/ext2/file.c              |   4 +-
 fs/ext4/file.c              |   4 +-
 fs/inode.c                  |   1 +
 fs/xfs/xfs_file.c           |   7 +-
 include/linux/dax.h         |   7 ++
 include/linux/fs.h          |   1 +
 include/linux/pagemap.h     |   3 +
 include/linux/pmem.h        |  22 +++++-
 include/linux/radix-tree.h  |   9 +++
 mm/filemap.c                |  84 ++++++++++++++++++++++-
 mm/truncate.c               |  64 ++++++++++--------
 mm/vmscan.c                 |   9 ++-
 15 files changed, 339 insertions(+), 49 deletions(-)

-- 
2.5.0

[PATCH v5 0/7] DAX fsync/msync support

[Ross Zwisler]

Changes from v4:
 - Explicity prevent shadow entries from being added to radix trees for DAX
   mappings in patch 2.  The only shadow entries that would be generated
   for DAX radix trees would be to track zero page mappings that were
   created for holes.  These pages would receive minimal benefit from
   having shadow entries, and the choice to have only one type of
   exceptional entry in a given radix tree makes the logic simpler both in
   clear_exceptional_entry() and in the rest of DAX.  (Jan)

 - Added Reviewed-by from Jan to patch 3.

This series is built upon ext4/master.  A working tree with this series
applied can be found here:

https://git.kernel.org/cgit/linux/kernel/git/zwisler/linux.git/log/?h=fsync_v5

Ross Zwisler (7):
  pmem: add wb_cache_pmem() to the PMEM API
  dax: support dirty DAX entries in radix tree
  mm: add find_get_entries_tag()
  dax: add support for fsync/sync
  ext2: call dax_pfn_mkwrite() for DAX fsync/msync
  ext4: call dax_pfn_mkwrite() for DAX fsync/msync
  xfs: call dax_pfn_mkwrite() for DAX fsync/msync

 arch/x86/include/asm/pmem.h |  11 +--
 fs/block_dev.c              |   3 +-
 fs/dax.c                    | 159 ++++++++++++++++++++++++++++++++++++++++++--
 fs/ext2/file.c              |   4 +-
 fs/ext4/file.c              |   4 +-
 fs/inode.c                  |   1 +
 fs/xfs/xfs_file.c           |   7 +-
 include/linux/dax.h         |   7 ++
 include/linux/fs.h          |   1 +
 include/linux/pagemap.h     |   3 +
 include/linux/pmem.h        |  22 +++++-
 include/linux/radix-tree.h  |   9 +++
 mm/filemap.c                |  84 ++++++++++++++++++++++-
 mm/truncate.c               |  64 ++++++++++--------
 mm/vmscan.c                 |   9 ++-
 15 files changed, 339 insertions(+), 49 deletions(-)

-- 
2.5.0

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[PATCH v5 1/7] pmem: add wb_cache_pmem() to the PMEM API

[Ross Zwisler]

The function __arch_wb_cache_pmem() was already an internal implementation
detail of the x86 PMEM API, but this functionality needs to be exported as
part of the general PMEM API to handle the fsync/msync case for DAX mmaps.

One thing worth noting is that we really do want this to be part of the
PMEM API as opposed to a stand-alone function like clflush_cache_range()
because of ordering restrictions.  By having wb_cache_pmem() as part of the
PMEM API we can leave it unordered, call it multiple times to write back
large amounts of memory, and then order the multiple calls with a single
wmb_pmem().

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
---
 arch/x86/include/asm/pmem.h | 11 ++++++-----
 include/linux/pmem.h        | 22 +++++++++++++++++++++-
 2 files changed, 27 insertions(+), 6 deletions(-)

diff --git a/arch/x86/include/asm/pmem.h b/arch/x86/include/asm/pmem.h
index d8ce3ec..6c7ade0 100644
--- a/arch/x86/include/asm/pmem.h
+++ b/arch/x86/include/asm/pmem.h
@@ -67,18 +67,19 @@ static inline void arch_wmb_pmem(void)
 }
 
 /**
- * __arch_wb_cache_pmem - write back a cache range with CLWB
+ * arch_wb_cache_pmem - write back a cache range with CLWB
  * @vaddr:	virtual start address
  * @size:	number of bytes to write back
  *
  * Write back a cache range using the CLWB (cache line write back)
  * instruction.  This function requires explicit ordering with an
- * arch_wmb_pmem() call.  This API is internal to the x86 PMEM implementation.
+ * arch_wmb_pmem() call.
  */
-static inline void __arch_wb_cache_pmem(void *vaddr, size_t size)
+static inline void arch_wb_cache_pmem(void __pmem *addr, size_t size)
 {
 	u16 x86_clflush_size = boot_cpu_data.x86_clflush_size;
 	unsigned long clflush_mask = x86_clflush_size - 1;
+	void *vaddr = (void __force *)addr;
 	void *vend = vaddr + size;
 	void *p;
 
@@ -115,7 +116,7 @@ static inline size_t arch_copy_from_iter_pmem(void __pmem *addr, size_t bytes,
 	len = copy_from_iter_nocache(vaddr, bytes, i);
 
 	if (__iter_needs_pmem_wb(i))
-		__arch_wb_cache_pmem(vaddr, bytes);
+		arch_wb_cache_pmem(addr, bytes);
 
 	return len;
 }
@@ -138,7 +139,7 @@ static inline void arch_clear_pmem(void __pmem *addr, size_t size)
 	else
 		memset(vaddr, 0, size);
 
-	__arch_wb_cache_pmem(vaddr, size);
+	arch_wb_cache_pmem(addr, size);
 }
 
 static inline bool __arch_has_wmb_pmem(void)
diff --git a/include/linux/pmem.h b/include/linux/pmem.h
index acfea8c..7c3d11a 100644
--- a/include/linux/pmem.h
+++ b/include/linux/pmem.h
@@ -53,12 +53,18 @@ static inline void arch_clear_pmem(void __pmem *addr, size_t size)
 {
 	BUG();
 }
+
+static inline void arch_wb_cache_pmem(void __pmem *addr, size_t size)
+{
+	BUG();
+}
 #endif
 
 /*
  * Architectures that define ARCH_HAS_PMEM_API must provide
  * implementations for arch_memcpy_to_pmem(), arch_wmb_pmem(),
- * arch_copy_from_iter_pmem(), arch_clear_pmem() and arch_has_wmb_pmem().
+ * arch_copy_from_iter_pmem(), arch_clear_pmem(), arch_wb_cache_pmem()
+ * and arch_has_wmb_pmem().
  */
 static inline void memcpy_from_pmem(void *dst, void __pmem const *src, size_t size)
 {
@@ -178,4 +184,18 @@ static inline void clear_pmem(void __pmem *addr, size_t size)
 	else
 		default_clear_pmem(addr, size);
 }
+
+/**
+ * wb_cache_pmem - write back processor cache for PMEM memory range
+ * @addr:	virtual start address
+ * @size:	number of bytes to write back
+ *
+ * Write back the processor cache range starting at 'addr' for 'size' bytes.
+ * This function requires explicit ordering with a wmb_pmem() call.
+ */
+static inline void wb_cache_pmem(void __pmem *addr, size_t size)
+{
+	if (arch_has_pmem_api())
+		arch_wb_cache_pmem(addr, size);
+}
 #endif /* __PMEM_H__ */
-- 
2.5.0

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[PATCH v5 1/7] pmem: add wb_cache_pmem() to the PMEM API

[Ross Zwisler]

The function __arch_wb_cache_pmem() was already an internal implementation
detail of the x86 PMEM API, but this functionality needs to be exported as
part of the general PMEM API to handle the fsync/msync case for DAX mmaps.

One thing worth noting is that we really do want this to be part of the
PMEM API as opposed to a stand-alone function like clflush_cache_range()
because of ordering restrictions.  By having wb_cache_pmem() as part of the
PMEM API we can leave it unordered, call it multiple times to write back
large amounts of memory, and then order the multiple calls with a single
wmb_pmem().

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
---
 arch/x86/include/asm/pmem.h | 11 ++++++-----
 include/linux/pmem.h        | 22 +++++++++++++++++++++-
 2 files changed, 27 insertions(+), 6 deletions(-)

diff --git a/arch/x86/include/asm/pmem.h b/arch/x86/include/asm/pmem.h
index d8ce3ec..6c7ade0 100644
--- a/arch/x86/include/asm/pmem.h
+++ b/arch/x86/include/asm/pmem.h
@@ -67,18 +67,19 @@ static inline void arch_wmb_pmem(void)
 }
 
 /**
- * __arch_wb_cache_pmem - write back a cache range with CLWB
+ * arch_wb_cache_pmem - write back a cache range with CLWB
  * @vaddr:	virtual start address
  * @size:	number of bytes to write back
  *
  * Write back a cache range using the CLWB (cache line write back)
  * instruction.  This function requires explicit ordering with an
- * arch_wmb_pmem() call.  This API is internal to the x86 PMEM implementation.
+ * arch_wmb_pmem() call.
  */
-static inline void __arch_wb_cache_pmem(void *vaddr, size_t size)
+static inline void arch_wb_cache_pmem(void __pmem *addr, size_t size)
 {
 	u16 x86_clflush_size = boot_cpu_data.x86_clflush_size;
 	unsigned long clflush_mask = x86_clflush_size - 1;
+	void *vaddr = (void __force *)addr;
 	void *vend = vaddr + size;
 	void *p;
 
@@ -115,7 +116,7 @@ static inline size_t arch_copy_from_iter_pmem(void __pmem *addr, size_t bytes,
 	len = copy_from_iter_nocache(vaddr, bytes, i);
 
 	if (__iter_needs_pmem_wb(i))
-		__arch_wb_cache_pmem(vaddr, bytes);
+		arch_wb_cache_pmem(addr, bytes);
 
 	return len;
 }
@@ -138,7 +139,7 @@ static inline void arch_clear_pmem(void __pmem *addr, size_t size)
 	else
 		memset(vaddr, 0, size);
 
-	__arch_wb_cache_pmem(vaddr, size);
+	arch_wb_cache_pmem(addr, size);
 }
 
 static inline bool __arch_has_wmb_pmem(void)
diff --git a/include/linux/pmem.h b/include/linux/pmem.h
index acfea8c..7c3d11a 100644
--- a/include/linux/pmem.h
+++ b/include/linux/pmem.h
@@ -53,12 +53,18 @@ static inline void arch_clear_pmem(void __pmem *addr, size_t size)
 {
 	BUG();
 }
+
+static inline void arch_wb_cache_pmem(void __pmem *addr, size_t size)
+{
+	BUG();
+}
 #endif
 
 /*
  * Architectures that define ARCH_HAS_PMEM_API must provide
  * implementations for arch_memcpy_to_pmem(), arch_wmb_pmem(),
- * arch_copy_from_iter_pmem(), arch_clear_pmem() and arch_has_wmb_pmem().
+ * arch_copy_from_iter_pmem(), arch_clear_pmem(), arch_wb_cache_pmem()
+ * and arch_has_wmb_pmem().
  */
 static inline void memcpy_from_pmem(void *dst, void __pmem const *src, size_t size)
 {
@@ -178,4 +184,18 @@ static inline void clear_pmem(void __pmem *addr, size_t size)
 	else
 		default_clear_pmem(addr, size);
 }
+
+/**
+ * wb_cache_pmem - write back processor cache for PMEM memory range
+ * @addr:	virtual start address
+ * @size:	number of bytes to write back
+ *
+ * Write back the processor cache range starting at 'addr' for 'size' bytes.
+ * This function requires explicit ordering with a wmb_pmem() call.
+ */
+static inline void wb_cache_pmem(void __pmem *addr, size_t size)
+{
+	if (arch_has_pmem_api())
+		arch_wb_cache_pmem(addr, size);
+}
 #endif /* __PMEM_H__ */
-- 
2.5.0

[PATCH v5 1/7] pmem: add wb_cache_pmem() to the PMEM API

[Ross Zwisler]

The function __arch_wb_cache_pmem() was already an internal implementation
detail of the x86 PMEM API, but this functionality needs to be exported as
part of the general PMEM API to handle the fsync/msync case for DAX mmaps.

One thing worth noting is that we really do want this to be part of the
PMEM API as opposed to a stand-alone function like clflush_cache_range()
because of ordering restrictions.  By having wb_cache_pmem() as part of the
PMEM API we can leave it unordered, call it multiple times to write back
large amounts of memory, and then order the multiple calls with a single
wmb_pmem().

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
---
 arch/x86/include/asm/pmem.h | 11 ++++++-----
 include/linux/pmem.h        | 22 +++++++++++++++++++++-
 2 files changed, 27 insertions(+), 6 deletions(-)

diff --git a/arch/x86/include/asm/pmem.h b/arch/x86/include/asm/pmem.h
index d8ce3ec..6c7ade0 100644
--- a/arch/x86/include/asm/pmem.h
+++ b/arch/x86/include/asm/pmem.h
@@ -67,18 +67,19 @@ static inline void arch_wmb_pmem(void)
 }
 
 /**
- * __arch_wb_cache_pmem - write back a cache range with CLWB
+ * arch_wb_cache_pmem - write back a cache range with CLWB
  * @vaddr:	virtual start address
  * @size:	number of bytes to write back
  *
  * Write back a cache range using the CLWB (cache line write back)
  * instruction.  This function requires explicit ordering with an
- * arch_wmb_pmem() call.  This API is internal to the x86 PMEM implementation.
+ * arch_wmb_pmem() call.
  */
-static inline void __arch_wb_cache_pmem(void *vaddr, size_t size)
+static inline void arch_wb_cache_pmem(void __pmem *addr, size_t size)
 {
 	u16 x86_clflush_size = boot_cpu_data.x86_clflush_size;
 	unsigned long clflush_mask = x86_clflush_size - 1;
+	void *vaddr = (void __force *)addr;
 	void *vend = vaddr + size;
 	void *p;
 
@@ -115,7 +116,7 @@ static inline size_t arch_copy_from_iter_pmem(void __pmem *addr, size_t bytes,
 	len = copy_from_iter_nocache(vaddr, bytes, i);
 
 	if (__iter_needs_pmem_wb(i))
-		__arch_wb_cache_pmem(vaddr, bytes);
+		arch_wb_cache_pmem(addr, bytes);
 
 	return len;
 }
@@ -138,7 +139,7 @@ static inline void arch_clear_pmem(void __pmem *addr, size_t size)
 	else
 		memset(vaddr, 0, size);
 
-	__arch_wb_cache_pmem(vaddr, size);
+	arch_wb_cache_pmem(addr, size);
 }
 
 static inline bool __arch_has_wmb_pmem(void)
diff --git a/include/linux/pmem.h b/include/linux/pmem.h
index acfea8c..7c3d11a 100644
--- a/include/linux/pmem.h
+++ b/include/linux/pmem.h
@@ -53,12 +53,18 @@ static inline void arch_clear_pmem(void __pmem *addr, size_t size)
 {
 	BUG();
 }
+
+static inline void arch_wb_cache_pmem(void __pmem *addr, size_t size)
+{
+	BUG();
+}
 #endif
 
 /*
  * Architectures that define ARCH_HAS_PMEM_API must provide
  * implementations for arch_memcpy_to_pmem(), arch_wmb_pmem(),
- * arch_copy_from_iter_pmem(), arch_clear_pmem() and arch_has_wmb_pmem().
+ * arch_copy_from_iter_pmem(), arch_clear_pmem(), arch_wb_cache_pmem()
+ * and arch_has_wmb_pmem().
  */
 static inline void memcpy_from_pmem(void *dst, void __pmem const *src, size_t size)
 {
@@ -178,4 +184,18 @@ static inline void clear_pmem(void __pmem *addr, size_t size)
 	else
 		default_clear_pmem(addr, size);
 }
+
+/**
+ * wb_cache_pmem - write back processor cache for PMEM memory range
+ * @addr:	virtual start address
+ * @size:	number of bytes to write back
+ *
+ * Write back the processor cache range starting at 'addr' for 'size' bytes.
+ * This function requires explicit ordering with a wmb_pmem() call.
+ */
+static inline void wb_cache_pmem(void __pmem *addr, size_t size)
+{
+	if (arch_has_pmem_api())
+		arch_wb_cache_pmem(addr, size);
+}
 #endif /* __PMEM_H__ */
-- 
2.5.0

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[PATCH v5 2/7] dax: support dirty DAX entries in radix tree

[Ross Zwisler]

Add support for tracking dirty DAX entries in the struct address_space
radix tree.  This tree is already used for dirty page writeback, and it
already supports the use of exceptional (non struct page*) entries.

In order to properly track dirty DAX pages we will insert new exceptional
entries into the radix tree that represent dirty DAX PTE or PMD pages.
These exceptional entries will also contain the writeback addresses for the
PTE or PMD faults that we can use at fsync/msync time.

There are currently two types of exceptional entries (shmem and shadow)
that can be placed into the radix tree, and this adds a third.  We rely on
the fact that only one type of exceptional entry can be found in a given
radix tree based on its usage.  This happens for free with DAX vs shmem but
we explicitly prevent shadow entries from being added to radix trees for
DAX mappings.

The only shadow entries that would be generated for DAX radix trees would
be to track zero page mappings that were created for holes.  These pages
would receive minimal benefit from having shadow entries, and the choice
to have only one type of exceptional entry in a given radix tree makes the
logic simpler both in clear_exceptional_entry() and in the rest of DAX.

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
---
 fs/block_dev.c             |  3 ++-
 fs/inode.c                 |  1 +
 include/linux/dax.h        |  5 ++++
 include/linux/fs.h         |  1 +
 include/linux/radix-tree.h |  9 +++++++
 mm/filemap.c               | 13 +++++++---
 mm/truncate.c              | 64 +++++++++++++++++++++++++++-------------------
 mm/vmscan.c                |  9 ++++++-
 8 files changed, 73 insertions(+), 32 deletions(-)

diff --git a/fs/block_dev.c b/fs/block_dev.c
index c25639e..226dacc 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -75,7 +75,8 @@ void kill_bdev(struct block_device *bdev)
 {
 	struct address_space *mapping = bdev->bd_inode->i_mapping;
 
-	if (mapping->nrpages == 0 && mapping->nrshadows == 0)
+	if (mapping->nrpages == 0 && mapping->nrshadows == 0 &&
+			mapping->nrdax == 0)
 		return;
 
 	invalidate_bh_lrus();
diff --git a/fs/inode.c b/fs/inode.c
index 1be5f90..79d828f 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -496,6 +496,7 @@ void clear_inode(struct inode *inode)
 	spin_lock_irq(&inode->i_data.tree_lock);
 	BUG_ON(inode->i_data.nrpages);
 	BUG_ON(inode->i_data.nrshadows);
+	BUG_ON(inode->i_data.nrdax);
 	spin_unlock_irq(&inode->i_data.tree_lock);
 	BUG_ON(!list_empty(&inode->i_data.private_list));
 	BUG_ON(!(inode->i_state & I_FREEING));
diff --git a/include/linux/dax.h b/include/linux/dax.h
index b415e52..e9d57f68 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -36,4 +36,9 @@ static inline bool vma_is_dax(struct vm_area_struct *vma)
 {
 	return vma->vm_file && IS_DAX(vma->vm_file->f_mapping->host);
 }
+
+static inline bool dax_mapping(struct address_space *mapping)
+{
+	return mapping->host && IS_DAX(mapping->host);
+}
 #endif
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 3aa5142..b9ac534 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -433,6 +433,7 @@ struct address_space {
 	/* Protected by tree_lock together with the radix tree */
 	unsigned long		nrpages;	/* number of total pages */
 	unsigned long		nrshadows;	/* number of shadow entries */
+	unsigned long		nrdax;	        /* number of DAX entries */
 	pgoff_t			writeback_index;/* writeback starts here */
 	const struct address_space_operations *a_ops;	/* methods */
 	unsigned long		flags;		/* error bits/gfp mask */
diff --git a/include/linux/radix-tree.h b/include/linux/radix-tree.h
index 33170db..f793c99 100644
--- a/include/linux/radix-tree.h
+++ b/include/linux/radix-tree.h
@@ -51,6 +51,15 @@
 #define RADIX_TREE_EXCEPTIONAL_ENTRY	2
 #define RADIX_TREE_EXCEPTIONAL_SHIFT	2
 
+#define RADIX_DAX_MASK	0xf
+#define RADIX_DAX_PTE  (0x4 | RADIX_TREE_EXCEPTIONAL_ENTRY)
+#define RADIX_DAX_PMD  (0x8 | RADIX_TREE_EXCEPTIONAL_ENTRY)
+#define RADIX_DAX_TYPE(entry) ((__force unsigned long)entry & RADIX_DAX_MASK)
+#define RADIX_DAX_ADDR(entry) ((void __pmem *)((unsigned long)entry & \
+			~RADIX_DAX_MASK))
+#define RADIX_DAX_ENTRY(addr, pmd) ((void *)((__force unsigned long)addr | \
+			(pmd ? RADIX_DAX_PMD : RADIX_DAX_PTE)))
+
 static inline int radix_tree_is_indirect_ptr(void *ptr)
 {
 	return (int)((unsigned long)ptr & RADIX_TREE_INDIRECT_PTR);
diff --git a/mm/filemap.c b/mm/filemap.c
index 1bb0076..167a4d9 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -11,6 +11,7 @@
  */
 #include <linux/export.h>
 #include <linux/compiler.h>
+#include <linux/dax.h>
 #include <linux/fs.h>
 #include <linux/uaccess.h>
 #include <linux/capability.h>
@@ -579,6 +580,12 @@ static int page_cache_tree_insert(struct address_space *mapping,
 		p = radix_tree_deref_slot_protected(slot, &mapping->tree_lock);
 		if (!radix_tree_exceptional_entry(p))
 			return -EEXIST;
+
+		if (dax_mapping(mapping)) {
+			WARN_ON(1);
+			return -EINVAL;
+		}
+
 		if (shadowp)
 			*shadowp = p;
 		mapping->nrshadows--;
@@ -1242,9 +1249,9 @@ repeat:
 			if (radix_tree_deref_retry(page))
 				goto restart;
 			/*
-			 * A shadow entry of a recently evicted page,
-			 * or a swap entry from shmem/tmpfs.  Return
-			 * it without attempting to raise page count.
+			 * A shadow entry of a recently evicted page, a swap
+			 * entry from shmem/tmpfs or a DAX entry.  Return it
+			 * without attempting to raise page count.
 			 */
 			goto export;
 		}
diff --git a/mm/truncate.c b/mm/truncate.c
index 76e35ad..1dc9f29 100644
--- a/mm/truncate.c
+++ b/mm/truncate.c
@@ -9,6 +9,7 @@
 
 #include <linux/kernel.h>
 #include <linux/backing-dev.h>
+#include <linux/dax.h>
 #include <linux/gfp.h>
 #include <linux/mm.h>
 #include <linux/swap.h>
@@ -34,31 +35,39 @@ static void clear_exceptional_entry(struct address_space *mapping,
 		return;
 
 	spin_lock_irq(&mapping->tree_lock);
-	/*
-	 * Regular page slots are stabilized by the page lock even
-	 * without the tree itself locked.  These unlocked entries
-	 * need verification under the tree lock.
-	 */
-	if (!__radix_tree_lookup(&mapping->page_tree, index, &node, &slot))
-		goto unlock;
-	if (*slot != entry)
-		goto unlock;
-	radix_tree_replace_slot(slot, NULL);
-	mapping->nrshadows--;
-	if (!node)
-		goto unlock;
-	workingset_node_shadows_dec(node);
-	/*
-	 * Don't track node without shadow entries.
-	 *
-	 * Avoid acquiring the list_lru lock if already untracked.
-	 * The list_empty() test is safe as node->private_list is
-	 * protected by mapping->tree_lock.
-	 */
-	if (!workingset_node_shadows(node) &&
-	    !list_empty(&node->private_list))
-		list_lru_del(&workingset_shadow_nodes, &node->private_list);
-	__radix_tree_delete_node(&mapping->page_tree, node);
+
+	if (dax_mapping(mapping)) {
+		if (radix_tree_delete_item(&mapping->page_tree, index, entry))
+			mapping->nrdax--;
+	} else {
+		/*
+		 * Regular page slots are stabilized by the page lock even
+		 * without the tree itself locked.  These unlocked entries
+		 * need verification under the tree lock.
+		 */
+		if (!__radix_tree_lookup(&mapping->page_tree, index, &node,
+					&slot))
+			goto unlock;
+		if (*slot != entry)
+			goto unlock;
+		radix_tree_replace_slot(slot, NULL);
+		mapping->nrshadows--;
+		if (!node)
+			goto unlock;
+		workingset_node_shadows_dec(node);
+		/*
+		 * Don't track node without shadow entries.
+		 *
+		 * Avoid acquiring the list_lru lock if already untracked.
+		 * The list_empty() test is safe as node->private_list is
+		 * protected by mapping->tree_lock.
+		 */
+		if (!workingset_node_shadows(node) &&
+		    !list_empty(&node->private_list))
+			list_lru_del(&workingset_shadow_nodes,
+					&node->private_list);
+		__radix_tree_delete_node(&mapping->page_tree, node);
+	}
 unlock:
 	spin_unlock_irq(&mapping->tree_lock);
 }
@@ -228,7 +237,8 @@ void truncate_inode_pages_range(struct address_space *mapping,
 	int		i;
 
 	cleancache_invalidate_inode(mapping);
-	if (mapping->nrpages == 0 && mapping->nrshadows == 0)
+	if (mapping->nrpages == 0 && mapping->nrshadows == 0 &&
+			mapping->nrdax == 0)
 		return;
 
 	/* Offsets within partial pages */
@@ -423,7 +433,7 @@ void truncate_inode_pages_final(struct address_space *mapping)
 	smp_rmb();
 	nrshadows = mapping->nrshadows;
 
-	if (nrpages || nrshadows) {
+	if (nrpages || nrshadows || mapping->nrdax) {
 		/*
 		 * As truncation uses a lockless tree lookup, cycle
 		 * the tree lock to make sure any ongoing tree
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 2aec424..8071956 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -46,6 +46,7 @@
 #include <linux/oom.h>
 #include <linux/prefetch.h>
 #include <linux/printk.h>
+#include <linux/dax.h>
 
 #include <asm/tlbflush.h>
 #include <asm/div64.h>
@@ -671,9 +672,15 @@ static int __remove_mapping(struct address_space *mapping, struct page *page,
 		 * inode reclaim needs to empty out the radix tree or
 		 * the nodes are lost.  Don't plant shadows behind its
 		 * back.
+		 *
+		 * We also don't store shadows for DAX mappings because the
+		 * only page cache pages found in these are zero pages
+		 * covering holes, and because we don't want to mix DAX
+		 * exceptional entries and shadow exceptional entries in the
+		 * same page_tree.
 		 */
 		if (reclaimed && page_is_file_cache(page) &&
-		    !mapping_exiting(mapping))
+		    !mapping_exiting(mapping) && !dax_mapping(mapping))
 			shadow = workingset_eviction(mapping, page);
 		__delete_from_page_cache(page, shadow, memcg);
 		spin_unlock_irqrestore(&mapping->tree_lock, flags);
-- 
2.5.0

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[PATCH v5 2/7] dax: support dirty DAX entries in radix tree

[Ross Zwisler]

Add support for tracking dirty DAX entries in the struct address_space
radix tree.  This tree is already used for dirty page writeback, and it
already supports the use of exceptional (non struct page*) entries.

In order to properly track dirty DAX pages we will insert new exceptional
entries into the radix tree that represent dirty DAX PTE or PMD pages.
These exceptional entries will also contain the writeback addresses for the
PTE or PMD faults that we can use at fsync/msync time.

There are currently two types of exceptional entries (shmem and shadow)
that can be placed into the radix tree, and this adds a third.  We rely on
the fact that only one type of exceptional entry can be found in a given
radix tree based on its usage.  This happens for free with DAX vs shmem but
we explicitly prevent shadow entries from being added to radix trees for
DAX mappings.

The only shadow entries that would be generated for DAX radix trees would
be to track zero page mappings that were created for holes.  These pages
would receive minimal benefit from having shadow entries, and the choice
to have only one type of exceptional entry in a given radix tree makes the
logic simpler both in clear_exceptional_entry() and in the rest of DAX.

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
---
 fs/block_dev.c             |  3 ++-
 fs/inode.c                 |  1 +
 include/linux/dax.h        |  5 ++++
 include/linux/fs.h         |  1 +
 include/linux/radix-tree.h |  9 +++++++
 mm/filemap.c               | 13 +++++++---
 mm/truncate.c              | 64 +++++++++++++++++++++++++++-------------------
 mm/vmscan.c                |  9 ++++++-
 8 files changed, 73 insertions(+), 32 deletions(-)

diff --git a/fs/block_dev.c b/fs/block_dev.c
index c25639e..226dacc 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -75,7 +75,8 @@ void kill_bdev(struct block_device *bdev)
 {
 	struct address_space *mapping = bdev->bd_inode->i_mapping;
 
-	if (mapping->nrpages == 0 && mapping->nrshadows == 0)
+	if (mapping->nrpages == 0 && mapping->nrshadows == 0 &&
+			mapping->nrdax == 0)
 		return;
 
 	invalidate_bh_lrus();
diff --git a/fs/inode.c b/fs/inode.c
index 1be5f90..79d828f 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -496,6 +496,7 @@ void clear_inode(struct inode *inode)
 	spin_lock_irq(&inode->i_data.tree_lock);
 	BUG_ON(inode->i_data.nrpages);
 	BUG_ON(inode->i_data.nrshadows);
+	BUG_ON(inode->i_data.nrdax);
 	spin_unlock_irq(&inode->i_data.tree_lock);
 	BUG_ON(!list_empty(&inode->i_data.private_list));
 	BUG_ON(!(inode->i_state & I_FREEING));
diff --git a/include/linux/dax.h b/include/linux/dax.h
index b415e52..e9d57f68 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -36,4 +36,9 @@ static inline bool vma_is_dax(struct vm_area_struct *vma)
 {
 	return vma->vm_file && IS_DAX(vma->vm_file->f_mapping->host);
 }
+
+static inline bool dax_mapping(struct address_space *mapping)
+{
+	return mapping->host && IS_DAX(mapping->host);
+}
 #endif
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 3aa5142..b9ac534 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -433,6 +433,7 @@ struct address_space {
 	/* Protected by tree_lock together with the radix tree */
 	unsigned long		nrpages;	/* number of total pages */
 	unsigned long		nrshadows;	/* number of shadow entries */
+	unsigned long		nrdax;	        /* number of DAX entries */
 	pgoff_t			writeback_index;/* writeback starts here */
 	const struct address_space_operations *a_ops;	/* methods */
 	unsigned long		flags;		/* error bits/gfp mask */
diff --git a/include/linux/radix-tree.h b/include/linux/radix-tree.h
index 33170db..f793c99 100644
--- a/include/linux/radix-tree.h
+++ b/include/linux/radix-tree.h
@@ -51,6 +51,15 @@
 #define RADIX_TREE_EXCEPTIONAL_ENTRY	2
 #define RADIX_TREE_EXCEPTIONAL_SHIFT	2
 
+#define RADIX_DAX_MASK	0xf
+#define RADIX_DAX_PTE  (0x4 | RADIX_TREE_EXCEPTIONAL_ENTRY)
+#define RADIX_DAX_PMD  (0x8 | RADIX_TREE_EXCEPTIONAL_ENTRY)
+#define RADIX_DAX_TYPE(entry) ((__force unsigned long)entry & RADIX_DAX_MASK)
+#define RADIX_DAX_ADDR(entry) ((void __pmem *)((unsigned long)entry & \
+			~RADIX_DAX_MASK))
+#define RADIX_DAX_ENTRY(addr, pmd) ((void *)((__force unsigned long)addr | \
+			(pmd ? RADIX_DAX_PMD : RADIX_DAX_PTE)))
+
 static inline int radix_tree_is_indirect_ptr(void *ptr)
 {
 	return (int)((unsigned long)ptr & RADIX_TREE_INDIRECT_PTR);
diff --git a/mm/filemap.c b/mm/filemap.c
index 1bb0076..167a4d9 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -11,6 +11,7 @@
  */
 #include <linux/export.h>
 #include <linux/compiler.h>
+#include <linux/dax.h>
 #include <linux/fs.h>
 #include <linux/uaccess.h>
 #include <linux/capability.h>
@@ -579,6 +580,12 @@ static int page_cache_tree_insert(struct address_space *mapping,
 		p = radix_tree_deref_slot_protected(slot, &mapping->tree_lock);
 		if (!radix_tree_exceptional_entry(p))
 			return -EEXIST;
+
+		if (dax_mapping(mapping)) {
+			WARN_ON(1);
+			return -EINVAL;
+		}
+
 		if (shadowp)
 			*shadowp = p;
 		mapping->nrshadows--;
@@ -1242,9 +1249,9 @@ repeat:
 			if (radix_tree_deref_retry(page))
 				goto restart;
 			/*
-			 * A shadow entry of a recently evicted page,
-			 * or a swap entry from shmem/tmpfs.  Return
-			 * it without attempting to raise page count.
+			 * A shadow entry of a recently evicted page, a swap
+			 * entry from shmem/tmpfs or a DAX entry.  Return it
+			 * without attempting to raise page count.
 			 */
 			goto export;
 		}
diff --git a/mm/truncate.c b/mm/truncate.c
index 76e35ad..1dc9f29 100644
--- a/mm/truncate.c
+++ b/mm/truncate.c
@@ -9,6 +9,7 @@
 
 #include <linux/kernel.h>
 #include <linux/backing-dev.h>
+#include <linux/dax.h>
 #include <linux/gfp.h>
 #include <linux/mm.h>
 #include <linux/swap.h>
@@ -34,31 +35,39 @@ static void clear_exceptional_entry(struct address_space *mapping,
 		return;
 
 	spin_lock_irq(&mapping->tree_lock);
-	/*
-	 * Regular page slots are stabilized by the page lock even
-	 * without the tree itself locked.  These unlocked entries
-	 * need verification under the tree lock.
-	 */
-	if (!__radix_tree_lookup(&mapping->page_tree, index, &node, &slot))
-		goto unlock;
-	if (*slot != entry)
-		goto unlock;
-	radix_tree_replace_slot(slot, NULL);
-	mapping->nrshadows--;
-	if (!node)
-		goto unlock;
-	workingset_node_shadows_dec(node);
-	/*
-	 * Don't track node without shadow entries.
-	 *
-	 * Avoid acquiring the list_lru lock if already untracked.
-	 * The list_empty() test is safe as node->private_list is
-	 * protected by mapping->tree_lock.
-	 */
-	if (!workingset_node_shadows(node) &&
-	    !list_empty(&node->private_list))
-		list_lru_del(&workingset_shadow_nodes, &node->private_list);
-	__radix_tree_delete_node(&mapping->page_tree, node);
+
+	if (dax_mapping(mapping)) {
+		if (radix_tree_delete_item(&mapping->page_tree, index, entry))
+			mapping->nrdax--;
+	} else {
+		/*
+		 * Regular page slots are stabilized by the page lock even
+		 * without the tree itself locked.  These unlocked entries
+		 * need verification under the tree lock.
+		 */
+		if (!__radix_tree_lookup(&mapping->page_tree, index, &node,
+					&slot))
+			goto unlock;
+		if (*slot != entry)
+			goto unlock;
+		radix_tree_replace_slot(slot, NULL);
+		mapping->nrshadows--;
+		if (!node)
+			goto unlock;
+		workingset_node_shadows_dec(node);
+		/*
+		 * Don't track node without shadow entries.
+		 *
+		 * Avoid acquiring the list_lru lock if already untracked.
+		 * The list_empty() test is safe as node->private_list is
+		 * protected by mapping->tree_lock.
+		 */
+		if (!workingset_node_shadows(node) &&
+		    !list_empty(&node->private_list))
+			list_lru_del(&workingset_shadow_nodes,
+					&node->private_list);
+		__radix_tree_delete_node(&mapping->page_tree, node);
+	}
 unlock:
 	spin_unlock_irq(&mapping->tree_lock);
 }
@@ -228,7 +237,8 @@ void truncate_inode_pages_range(struct address_space *mapping,
 	int		i;
 
 	cleancache_invalidate_inode(mapping);
-	if (mapping->nrpages == 0 && mapping->nrshadows == 0)
+	if (mapping->nrpages == 0 && mapping->nrshadows == 0 &&
+			mapping->nrdax == 0)
 		return;
 
 	/* Offsets within partial pages */
@@ -423,7 +433,7 @@ void truncate_inode_pages_final(struct address_space *mapping)
 	smp_rmb();
 	nrshadows = mapping->nrshadows;
 
-	if (nrpages || nrshadows) {
+	if (nrpages || nrshadows || mapping->nrdax) {
 		/*
 		 * As truncation uses a lockless tree lookup, cycle
 		 * the tree lock to make sure any ongoing tree
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 2aec424..8071956 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -46,6 +46,7 @@
 #include <linux/oom.h>
 #include <linux/prefetch.h>
 #include <linux/printk.h>
+#include <linux/dax.h>
 
 #include <asm/tlbflush.h>
 #include <asm/div64.h>
@@ -671,9 +672,15 @@ static int __remove_mapping(struct address_space *mapping, struct page *page,
 		 * inode reclaim needs to empty out the radix tree or
 		 * the nodes are lost.  Don't plant shadows behind its
 		 * back.
+		 *
+		 * We also don't store shadows for DAX mappings because the
+		 * only page cache pages found in these are zero pages
+		 * covering holes, and because we don't want to mix DAX
+		 * exceptional entries and shadow exceptional entries in the
+		 * same page_tree.
 		 */
 		if (reclaimed && page_is_file_cache(page) &&
-		    !mapping_exiting(mapping))
+		    !mapping_exiting(mapping) && !dax_mapping(mapping))
 			shadow = workingset_eviction(mapping, page);
 		__delete_from_page_cache(page, shadow, memcg);
 		spin_unlock_irqrestore(&mapping->tree_lock, flags);
-- 
2.5.0

[PATCH v5 2/7] dax: support dirty DAX entries in radix tree

[Ross Zwisler]

Add support for tracking dirty DAX entries in the struct address_space
radix tree.  This tree is already used for dirty page writeback, and it
already supports the use of exceptional (non struct page*) entries.

In order to properly track dirty DAX pages we will insert new exceptional
entries into the radix tree that represent dirty DAX PTE or PMD pages.
These exceptional entries will also contain the writeback addresses for the
PTE or PMD faults that we can use at fsync/msync time.

There are currently two types of exceptional entries (shmem and shadow)
that can be placed into the radix tree, and this adds a third.  We rely on
the fact that only one type of exceptional entry can be found in a given
radix tree based on its usage.  This happens for free with DAX vs shmem but
we explicitly prevent shadow entries from being added to radix trees for
DAX mappings.

The only shadow entries that would be generated for DAX radix trees would
be to track zero page mappings that were created for holes.  These pages
would receive minimal benefit from having shadow entries, and the choice
to have only one type of exceptional entry in a given radix tree makes the
logic simpler both in clear_exceptional_entry() and in the rest of DAX.

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
---
 fs/block_dev.c             |  3 ++-
 fs/inode.c                 |  1 +
 include/linux/dax.h        |  5 ++++
 include/linux/fs.h         |  1 +
 include/linux/radix-tree.h |  9 +++++++
 mm/filemap.c               | 13 +++++++---
 mm/truncate.c              | 64 +++++++++++++++++++++++++++-------------------
 mm/vmscan.c                |  9 ++++++-
 8 files changed, 73 insertions(+), 32 deletions(-)

diff --git a/fs/block_dev.c b/fs/block_dev.c
index c25639e..226dacc 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -75,7 +75,8 @@ void kill_bdev(struct block_device *bdev)
 {
 	struct address_space *mapping = bdev->bd_inode->i_mapping;
 
-	if (mapping->nrpages == 0 && mapping->nrshadows == 0)
+	if (mapping->nrpages == 0 && mapping->nrshadows == 0 &&
+			mapping->nrdax == 0)
 		return;
 
 	invalidate_bh_lrus();
diff --git a/fs/inode.c b/fs/inode.c
index 1be5f90..79d828f 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -496,6 +496,7 @@ void clear_inode(struct inode *inode)
 	spin_lock_irq(&inode->i_data.tree_lock);
 	BUG_ON(inode->i_data.nrpages);
 	BUG_ON(inode->i_data.nrshadows);
+	BUG_ON(inode->i_data.nrdax);
 	spin_unlock_irq(&inode->i_data.tree_lock);
 	BUG_ON(!list_empty(&inode->i_data.private_list));
 	BUG_ON(!(inode->i_state & I_FREEING));
diff --git a/include/linux/dax.h b/include/linux/dax.h
index b415e52..e9d57f68 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -36,4 +36,9 @@ static inline bool vma_is_dax(struct vm_area_struct *vma)
 {
 	return vma->vm_file && IS_DAX(vma->vm_file->f_mapping->host);
 }
+
+static inline bool dax_mapping(struct address_space *mapping)
+{
+	return mapping->host && IS_DAX(mapping->host);
+}
 #endif
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 3aa5142..b9ac534 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -433,6 +433,7 @@ struct address_space {
 	/* Protected by tree_lock together with the radix tree */
 	unsigned long		nrpages;	/* number of total pages */
 	unsigned long		nrshadows;	/* number of shadow entries */
+	unsigned long		nrdax;	        /* number of DAX entries */
 	pgoff_t			writeback_index;/* writeback starts here */
 	const struct address_space_operations *a_ops;	/* methods */
 	unsigned long		flags;		/* error bits/gfp mask */
diff --git a/include/linux/radix-tree.h b/include/linux/radix-tree.h
index 33170db..f793c99 100644
--- a/include/linux/radix-tree.h
+++ b/include/linux/radix-tree.h
@@ -51,6 +51,15 @@
 #define RADIX_TREE_EXCEPTIONAL_ENTRY	2
 #define RADIX_TREE_EXCEPTIONAL_SHIFT	2
 
+#define RADIX_DAX_MASK	0xf
+#define RADIX_DAX_PTE  (0x4 | RADIX_TREE_EXCEPTIONAL_ENTRY)
+#define RADIX_DAX_PMD  (0x8 | RADIX_TREE_EXCEPTIONAL_ENTRY)
+#define RADIX_DAX_TYPE(entry) ((__force unsigned long)entry & RADIX_DAX_MASK)
+#define RADIX_DAX_ADDR(entry) ((void __pmem *)((unsigned long)entry & \
+			~RADIX_DAX_MASK))
+#define RADIX_DAX_ENTRY(addr, pmd) ((void *)((__force unsigned long)addr | \
+			(pmd ? RADIX_DAX_PMD : RADIX_DAX_PTE)))
+
 static inline int radix_tree_is_indirect_ptr(void *ptr)
 {
 	return (int)((unsigned long)ptr & RADIX_TREE_INDIRECT_PTR);
diff --git a/mm/filemap.c b/mm/filemap.c
index 1bb0076..167a4d9 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -11,6 +11,7 @@
  */
 #include <linux/export.h>
 #include <linux/compiler.h>
+#include <linux/dax.h>
 #include <linux/fs.h>
 #include <linux/uaccess.h>
 #include <linux/capability.h>
@@ -579,6 +580,12 @@ static int page_cache_tree_insert(struct address_space *mapping,
 		p = radix_tree_deref_slot_protected(slot, &mapping->tree_lock);
 		if (!radix_tree_exceptional_entry(p))
 			return -EEXIST;
+
+		if (dax_mapping(mapping)) {
+			WARN_ON(1);
+			return -EINVAL;
+		}
+
 		if (shadowp)
 			*shadowp = p;
 		mapping->nrshadows--;
@@ -1242,9 +1249,9 @@ repeat:
 			if (radix_tree_deref_retry(page))
 				goto restart;
 			/*
-			 * A shadow entry of a recently evicted page,
-			 * or a swap entry from shmem/tmpfs.  Return
-			 * it without attempting to raise page count.
+			 * A shadow entry of a recently evicted page, a swap
+			 * entry from shmem/tmpfs or a DAX entry.  Return it
+			 * without attempting to raise page count.
 			 */
 			goto export;
 		}
diff --git a/mm/truncate.c b/mm/truncate.c
index 76e35ad..1dc9f29 100644
--- a/mm/truncate.c
+++ b/mm/truncate.c
@@ -9,6 +9,7 @@
 
 #include <linux/kernel.h>
 #include <linux/backing-dev.h>
+#include <linux/dax.h>
 #include <linux/gfp.h>
 #include <linux/mm.h>
 #include <linux/swap.h>
@@ -34,31 +35,39 @@ static void clear_exceptional_entry(struct address_space *mapping,
 		return;
 
 	spin_lock_irq(&mapping->tree_lock);
-	/*
-	 * Regular page slots are stabilized by the page lock even
-	 * without the tree itself locked.  These unlocked entries
-	 * need verification under the tree lock.
-	 */
-	if (!__radix_tree_lookup(&mapping->page_tree, index, &node, &slot))
-		goto unlock;
-	if (*slot != entry)
-		goto unlock;
-	radix_tree_replace_slot(slot, NULL);
-	mapping->nrshadows--;
-	if (!node)
-		goto unlock;
-	workingset_node_shadows_dec(node);
-	/*
-	 * Don't track node without shadow entries.
-	 *
-	 * Avoid acquiring the list_lru lock if already untracked.
-	 * The list_empty() test is safe as node->private_list is
-	 * protected by mapping->tree_lock.
-	 */
-	if (!workingset_node_shadows(node) &&
-	    !list_empty(&node->private_list))
-		list_lru_del(&workingset_shadow_nodes, &node->private_list);
-	__radix_tree_delete_node(&mapping->page_tree, node);
+
+	if (dax_mapping(mapping)) {
+		if (radix_tree_delete_item(&mapping->page_tree, index, entry))
+			mapping->nrdax--;
+	} else {
+		/*
+		 * Regular page slots are stabilized by the page lock even
+		 * without the tree itself locked.  These unlocked entries
+		 * need verification under the tree lock.
+		 */
+		if (!__radix_tree_lookup(&mapping->page_tree, index, &node,
+					&slot))
+			goto unlock;
+		if (*slot != entry)
+			goto unlock;
+		radix_tree_replace_slot(slot, NULL);
+		mapping->nrshadows--;
+		if (!node)
+			goto unlock;
+		workingset_node_shadows_dec(node);
+		/*
+		 * Don't track node without shadow entries.
+		 *
+		 * Avoid acquiring the list_lru lock if already untracked.
+		 * The list_empty() test is safe as node->private_list is
+		 * protected by mapping->tree_lock.
+		 */
+		if (!workingset_node_shadows(node) &&
+		    !list_empty(&node->private_list))
+			list_lru_del(&workingset_shadow_nodes,
+					&node->private_list);
+		__radix_tree_delete_node(&mapping->page_tree, node);
+	}
 unlock:
 	spin_unlock_irq(&mapping->tree_lock);
 }
@@ -228,7 +237,8 @@ void truncate_inode_pages_range(struct address_space *mapping,
 	int		i;
 
 	cleancache_invalidate_inode(mapping);
-	if (mapping->nrpages == 0 && mapping->nrshadows == 0)
+	if (mapping->nrpages == 0 && mapping->nrshadows == 0 &&
+			mapping->nrdax == 0)
 		return;
 
 	/* Offsets within partial pages */
@@ -423,7 +433,7 @@ void truncate_inode_pages_final(struct address_space *mapping)
 	smp_rmb();
 	nrshadows = mapping->nrshadows;
 
-	if (nrpages || nrshadows) {
+	if (nrpages || nrshadows || mapping->nrdax) {
 		/*
 		 * As truncation uses a lockless tree lookup, cycle
 		 * the tree lock to make sure any ongoing tree
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 2aec424..8071956 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -46,6 +46,7 @@
 #include <linux/oom.h>
 #include <linux/prefetch.h>
 #include <linux/printk.h>
+#include <linux/dax.h>
 
 #include <asm/tlbflush.h>
 #include <asm/div64.h>
@@ -671,9 +672,15 @@ static int __remove_mapping(struct address_space *mapping, struct page *page,
 		 * inode reclaim needs to empty out the radix tree or
 		 * the nodes are lost.  Don't plant shadows behind its
 		 * back.
+		 *
+		 * We also don't store shadows for DAX mappings because the
+		 * only page cache pages found in these are zero pages
+		 * covering holes, and because we don't want to mix DAX
+		 * exceptional entries and shadow exceptional entries in the
+		 * same page_tree.
 		 */
 		if (reclaimed && page_is_file_cache(page) &&
-		    !mapping_exiting(mapping))
+		    !mapping_exiting(mapping) && !dax_mapping(mapping))
 			shadow = workingset_eviction(mapping, page);
 		__delete_from_page_cache(page, shadow, memcg);
 		spin_unlock_irqrestore(&mapping->tree_lock, flags);
-- 
2.5.0

_______________________________________________
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xfs@oss.sgi.com
http://oss.sgi.com/mailman/listinfo/xfs

[PATCH v5 3/7] mm: add find_get_entries_tag()

[Ross Zwisler]

Add find_get_entries_tag() to the family of functions that include
find_get_entries(), find_get_pages() and find_get_pages_tag().  This is
needed for DAX dirty page handling because we need a list of both page
offsets and radix tree entries ('indices' and 'entries' in this function)
that are marked with the PAGECACHE_TAG_TOWRITE tag.

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Reviewed-by: Jan Kara <jack@suse.cz>
---
 include/linux/pagemap.h |  3 +++
 mm/filemap.c            | 68 +++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 71 insertions(+)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 26eabf5..4db0425 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -361,6 +361,9 @@ unsigned find_get_pages_contig(struct address_space *mapping, pgoff_t start,
 			       unsigned int nr_pages, struct page **pages);
 unsigned find_get_pages_tag(struct address_space *mapping, pgoff_t *index,
 			int tag, unsigned int nr_pages, struct page **pages);
+unsigned find_get_entries_tag(struct address_space *mapping, pgoff_t start,
+			int tag, unsigned int nr_entries,
+			struct page **entries, pgoff_t *indices);
 
 struct page *grab_cache_page_write_begin(struct address_space *mapping,
 			pgoff_t index, unsigned flags);
diff --git a/mm/filemap.c b/mm/filemap.c
index 167a4d9..99dfbc9 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1498,6 +1498,74 @@ repeat:
 }
 EXPORT_SYMBOL(find_get_pages_tag);
 
+/**
+ * find_get_entries_tag - find and return entries that match @tag
+ * @mapping:	the address_space to search
+ * @start:	the starting page cache index
+ * @tag:	the tag index
+ * @nr_entries:	the maximum number of entries
+ * @entries:	where the resulting entries are placed
+ * @indices:	the cache indices corresponding to the entries in @entries
+ *
+ * Like find_get_entries, except we only return entries which are tagged with
+ * @tag.
+ */
+unsigned find_get_entries_tag(struct address_space *mapping, pgoff_t start,
+			int tag, unsigned int nr_entries,
+			struct page **entries, pgoff_t *indices)
+{
+	void **slot;
+	unsigned int ret = 0;
+	struct radix_tree_iter iter;
+
+	if (!nr_entries)
+		return 0;
+
+	rcu_read_lock();
+restart:
+	radix_tree_for_each_tagged(slot, &mapping->page_tree,
+				   &iter, start, tag) {
+		struct page *page;
+repeat:
+		page = radix_tree_deref_slot(slot);
+		if (unlikely(!page))
+			continue;
+		if (radix_tree_exception(page)) {
+			if (radix_tree_deref_retry(page)) {
+				/*
+				 * Transient condition which can only trigger
+				 * when entry at index 0 moves out of or back
+				 * to root: none yet gotten, safe to restart.
+				 */
+				goto restart;
+			}
+
+			/*
+			 * A shadow entry of a recently evicted page, a swap
+			 * entry from shmem/tmpfs or a DAX entry.  Return it
+			 * without attempting to raise page count.
+			 */
+			goto export;
+		}
+		if (!page_cache_get_speculative(page))
+			goto repeat;
+
+		/* Has the page moved? */
+		if (unlikely(page != *slot)) {
+			page_cache_release(page);
+			goto repeat;
+		}
+export:
+		indices[ret] = iter.index;
+		entries[ret] = page;
+		if (++ret == nr_entries)
+			break;
+	}
+	rcu_read_unlock();
+	return ret;
+}
+EXPORT_SYMBOL(find_get_entries_tag);
+
 /*
  * CD/DVDs are error prone. When a medium error occurs, the driver may fail
  * a _large_ part of the i/o request. Imagine the worst scenario:
-- 
2.5.0

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[PATCH v5 3/7] mm: add find_get_entries_tag()

[Ross Zwisler]

Add find_get_entries_tag() to the family of functions that include
find_get_entries(), find_get_pages() and find_get_pages_tag().  This is
needed for DAX dirty page handling because we need a list of both page
offsets and radix tree entries ('indices' and 'entries' in this function)
that are marked with the PAGECACHE_TAG_TOWRITE tag.

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Reviewed-by: Jan Kara <jack@suse.cz>
---
 include/linux/pagemap.h |  3 +++
 mm/filemap.c            | 68 +++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 71 insertions(+)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 26eabf5..4db0425 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -361,6 +361,9 @@ unsigned find_get_pages_contig(struct address_space *mapping, pgoff_t start,
 			       unsigned int nr_pages, struct page **pages);
 unsigned find_get_pages_tag(struct address_space *mapping, pgoff_t *index,
 			int tag, unsigned int nr_pages, struct page **pages);
+unsigned find_get_entries_tag(struct address_space *mapping, pgoff_t start,
+			int tag, unsigned int nr_entries,
+			struct page **entries, pgoff_t *indices);
 
 struct page *grab_cache_page_write_begin(struct address_space *mapping,
 			pgoff_t index, unsigned flags);
diff --git a/mm/filemap.c b/mm/filemap.c
index 167a4d9..99dfbc9 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1498,6 +1498,74 @@ repeat:
 }
 EXPORT_SYMBOL(find_get_pages_tag);
 
+/**
+ * find_get_entries_tag - find and return entries that match @tag
+ * @mapping:	the address_space to search
+ * @start:	the starting page cache index
+ * @tag:	the tag index
+ * @nr_entries:	the maximum number of entries
+ * @entries:	where the resulting entries are placed
+ * @indices:	the cache indices corresponding to the entries in @entries
+ *
+ * Like find_get_entries, except we only return entries which are tagged with
+ * @tag.
+ */
+unsigned find_get_entries_tag(struct address_space *mapping, pgoff_t start,
+			int tag, unsigned int nr_entries,
+			struct page **entries, pgoff_t *indices)
+{
+	void **slot;
+	unsigned int ret = 0;
+	struct radix_tree_iter iter;
+
+	if (!nr_entries)
+		return 0;
+
+	rcu_read_lock();
+restart:
+	radix_tree_for_each_tagged(slot, &mapping->page_tree,
+				   &iter, start, tag) {
+		struct page *page;
+repeat:
+		page = radix_tree_deref_slot(slot);
+		if (unlikely(!page))
+			continue;
+		if (radix_tree_exception(page)) {
+			if (radix_tree_deref_retry(page)) {
+				/*
+				 * Transient condition which can only trigger
+				 * when entry at index 0 moves out of or back
+				 * to root: none yet gotten, safe to restart.
+				 */
+				goto restart;
+			}
+
+			/*
+			 * A shadow entry of a recently evicted page, a swap
+			 * entry from shmem/tmpfs or a DAX entry.  Return it
+			 * without attempting to raise page count.
+			 */
+			goto export;
+		}
+		if (!page_cache_get_speculative(page))
+			goto repeat;
+
+		/* Has the page moved? */
+		if (unlikely(page != *slot)) {
+			page_cache_release(page);
+			goto repeat;
+		}
+export:
+		indices[ret] = iter.index;
+		entries[ret] = page;
+		if (++ret == nr_entries)
+			break;
+	}
+	rcu_read_unlock();
+	return ret;
+}
+EXPORT_SYMBOL(find_get_entries_tag);
+
 /*
  * CD/DVDs are error prone. When a medium error occurs, the driver may fail
  * a _large_ part of the i/o request. Imagine the worst scenario:
-- 
2.5.0

[PATCH v5 3/7] mm: add find_get_entries_tag()

[Ross Zwisler]

Add find_get_entries_tag() to the family of functions that include
find_get_entries(), find_get_pages() and find_get_pages_tag().  This is
needed for DAX dirty page handling because we need a list of both page
offsets and radix tree entries ('indices' and 'entries' in this function)
that are marked with the PAGECACHE_TAG_TOWRITE tag.

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Reviewed-by: Jan Kara <jack@suse.cz>
---
 include/linux/pagemap.h |  3 +++
 mm/filemap.c            | 68 +++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 71 insertions(+)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 26eabf5..4db0425 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -361,6 +361,9 @@ unsigned find_get_pages_contig(struct address_space *mapping, pgoff_t start,
 			       unsigned int nr_pages, struct page **pages);
 unsigned find_get_pages_tag(struct address_space *mapping, pgoff_t *index,
 			int tag, unsigned int nr_pages, struct page **pages);
+unsigned find_get_entries_tag(struct address_space *mapping, pgoff_t start,
+			int tag, unsigned int nr_entries,
+			struct page **entries, pgoff_t *indices);
 
 struct page *grab_cache_page_write_begin(struct address_space *mapping,
 			pgoff_t index, unsigned flags);
diff --git a/mm/filemap.c b/mm/filemap.c
index 167a4d9..99dfbc9 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1498,6 +1498,74 @@ repeat:
 }
 EXPORT_SYMBOL(find_get_pages_tag);
 
+/**
+ * find_get_entries_tag - find and return entries that match @tag
+ * @mapping:	the address_space to search
+ * @start:	the starting page cache index
+ * @tag:	the tag index
+ * @nr_entries:	the maximum number of entries
+ * @entries:	where the resulting entries are placed
+ * @indices:	the cache indices corresponding to the entries in @entries
+ *
+ * Like find_get_entries, except we only return entries which are tagged with
+ * @tag.
+ */
+unsigned find_get_entries_tag(struct address_space *mapping, pgoff_t start,
+			int tag, unsigned int nr_entries,
+			struct page **entries, pgoff_t *indices)
+{
+	void **slot;
+	unsigned int ret = 0;
+	struct radix_tree_iter iter;
+
+	if (!nr_entries)
+		return 0;
+
+	rcu_read_lock();
+restart:
+	radix_tree_for_each_tagged(slot, &mapping->page_tree,
+				   &iter, start, tag) {
+		struct page *page;
+repeat:
+		page = radix_tree_deref_slot(slot);
+		if (unlikely(!page))
+			continue;
+		if (radix_tree_exception(page)) {
+			if (radix_tree_deref_retry(page)) {
+				/*
+				 * Transient condition which can only trigger
+				 * when entry at index 0 moves out of or back
+				 * to root: none yet gotten, safe to restart.
+				 */
+				goto restart;
+			}
+
+			/*
+			 * A shadow entry of a recently evicted page, a swap
+			 * entry from shmem/tmpfs or a DAX entry.  Return it
+			 * without attempting to raise page count.
+			 */
+			goto export;
+		}
+		if (!page_cache_get_speculative(page))
+			goto repeat;
+
+		/* Has the page moved? */
+		if (unlikely(page != *slot)) {
+			page_cache_release(page);
+			goto repeat;
+		}
+export:
+		indices[ret] = iter.index;
+		entries[ret] = page;
+		if (++ret == nr_entries)
+			break;
+	}
+	rcu_read_unlock();
+	return ret;
+}
+EXPORT_SYMBOL(find_get_entries_tag);
+
 /*
  * CD/DVDs are error prone. When a medium error occurs, the driver may fail
  * a _large_ part of the i/o request. Imagine the worst scenario:
-- 
2.5.0

_______________________________________________
xfs mailing list
xfs@oss.sgi.com
http://oss.sgi.com/mailman/listinfo/xfs

[PATCH v5 4/7] dax: add support for fsync/sync

[Ross Zwisler]

To properly handle fsync/msync in an efficient way DAX needs to track dirty
pages so it is able to flush them durably to media on demand.

The tracking of dirty pages is done via the radix tree in struct
address_space.  This radix tree is already used by the page writeback
infrastructure for tracking dirty pages associated with an open file, and
it already has support for exceptional (non struct page*) entries.  We
build upon these features to add exceptional entries to the radix tree for
DAX dirty PMD or PTE pages at fault time.

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
---
 fs/dax.c            | 159 ++++++++++++++++++++++++++++++++++++++++++++++++++--
 include/linux/dax.h |   2 +
 mm/filemap.c        |   3 +
 3 files changed, 158 insertions(+), 6 deletions(-)

diff --git a/fs/dax.c b/fs/dax.c
index 43671b6..19347cf 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -24,6 +24,7 @@
 #include <linux/memcontrol.h>
 #include <linux/mm.h>
 #include <linux/mutex.h>
+#include <linux/pagevec.h>
 #include <linux/pmem.h>
 #include <linux/sched.h>
 #include <linux/uio.h>
@@ -289,6 +290,143 @@ static int copy_user_bh(struct page *to, struct buffer_head *bh,
 	return 0;
 }
 
+static int dax_radix_entry(struct address_space *mapping, pgoff_t index,
+		void __pmem *addr, bool pmd_entry, bool dirty)
+{
+	struct radix_tree_root *page_tree = &mapping->page_tree;
+	int error = 0;
+	void *entry;
+
+	__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
+
+	spin_lock_irq(&mapping->tree_lock);
+	entry = radix_tree_lookup(page_tree, index);
+
+	if (entry) {
+		if (!pmd_entry || RADIX_DAX_TYPE(entry) == RADIX_DAX_PMD)
+			goto dirty;
+		radix_tree_delete(&mapping->page_tree, index);
+		mapping->nrdax--;
+	}
+
+	if (!addr) {
+		/*
+		 * This can happen during correct operation if our pfn_mkwrite
+		 * fault raced against a hole punch operation.  If this
+		 * happens the pte that was hole punched will have been
+		 * unmapped and the radix tree entry will have been removed by
+		 * the time we are called, but the call will still happen.  We
+		 * will return all the way up to wp_pfn_shared(), where the
+		 * pte_same() check will fail, eventually causing page fault
+		 * to be retried by the CPU.
+		 */
+		goto unlock;
+	} else if (RADIX_DAX_TYPE(addr)) {
+		WARN_ONCE(1, "%s: invalid address %p\n", __func__, addr);
+		goto unlock;
+	}
+
+	error = radix_tree_insert(page_tree, index,
+			RADIX_DAX_ENTRY(addr, pmd_entry));
+	if (error)
+		goto unlock;
+
+	mapping->nrdax++;
+ dirty:
+	if (dirty)
+		radix_tree_tag_set(page_tree, index, PAGECACHE_TAG_DIRTY);
+ unlock:
+	spin_unlock_irq(&mapping->tree_lock);
+	return error;
+}
+
+static void dax_writeback_one(struct address_space *mapping, pgoff_t index,
+		void *entry)
+{
+	struct radix_tree_root *page_tree = &mapping->page_tree;
+	int type = RADIX_DAX_TYPE(entry);
+	struct radix_tree_node *node;
+	void **slot;
+
+	if (type != RADIX_DAX_PTE && type != RADIX_DAX_PMD) {
+		WARN_ON_ONCE(1);
+		return;
+	}
+
+	spin_lock_irq(&mapping->tree_lock);
+	/*
+	 * Regular page slots are stabilized by the page lock even
+	 * without the tree itself locked.  These unlocked entries
+	 * need verification under the tree lock.
+	 */
+	if (!__radix_tree_lookup(page_tree, index, &node, &slot))
+		goto unlock;
+	if (*slot != entry)
+		goto unlock;
+
+	/* another fsync thread may have already written back this entry */
+	if (!radix_tree_tag_get(page_tree, index, PAGECACHE_TAG_TOWRITE))
+		goto unlock;
+
+	radix_tree_tag_clear(page_tree, index, PAGECACHE_TAG_TOWRITE);
+
+	if (type == RADIX_DAX_PMD)
+		wb_cache_pmem(RADIX_DAX_ADDR(entry), PMD_SIZE);
+	else
+		wb_cache_pmem(RADIX_DAX_ADDR(entry), PAGE_SIZE);
+ unlock:
+	spin_unlock_irq(&mapping->tree_lock);
+}
+
+/*
+ * Flush the mapping to the persistent domain within the byte range of [start,
+ * end]. This is required by data integrity operations to ensure file data is
+ * on persistent storage prior to completion of the operation.
+ */
+void dax_writeback_mapping_range(struct address_space *mapping, loff_t start,
+		loff_t end)
+{
+	struct inode *inode = mapping->host;
+	pgoff_t indices[PAGEVEC_SIZE];
+	pgoff_t start_page, end_page;
+	struct pagevec pvec;
+	void *entry;
+	int i;
+
+	if (inode->i_blkbits != PAGE_SHIFT) {
+		WARN_ON_ONCE(1);
+		return;
+	}
+
+	rcu_read_lock();
+	entry = radix_tree_lookup(&mapping->page_tree, start & PMD_MASK);
+	rcu_read_unlock();
+
+	/* see if the start of our range is covered by a PMD entry */
+	if (entry && RADIX_DAX_TYPE(entry) == RADIX_DAX_PMD)
+		start &= PMD_MASK;
+
+	start_page = start >> PAGE_CACHE_SHIFT;
+	end_page = end >> PAGE_CACHE_SHIFT;
+
+	tag_pages_for_writeback(mapping, start_page, end_page);
+
+	pagevec_init(&pvec, 0);
+	while (1) {
+		pvec.nr = find_get_entries_tag(mapping, start_page,
+				PAGECACHE_TAG_TOWRITE, PAGEVEC_SIZE,
+				pvec.pages, indices);
+
+		if (pvec.nr == 0)
+			break;
+
+		for (i = 0; i < pvec.nr; i++)
+			dax_writeback_one(mapping, indices[i], pvec.pages[i]);
+	}
+	wmb_pmem();
+}
+EXPORT_SYMBOL_GPL(dax_writeback_mapping_range);
+
 static int dax_insert_mapping(struct inode *inode, struct buffer_head *bh,
 			struct vm_area_struct *vma, struct vm_fault *vmf)
 {
@@ -329,7 +467,11 @@ static int dax_insert_mapping(struct inode *inode, struct buffer_head *bh,
 	}
 
 	error = vm_insert_mixed(vma, vaddr, pfn);
+	if (error)
+		goto out;
 
+	error = dax_radix_entry(mapping, vmf->pgoff, addr, false,
+			vmf->flags & FAULT_FLAG_WRITE);
  out:
 	i_mmap_unlock_read(mapping);
 
@@ -452,6 +594,7 @@ int __dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
 		delete_from_page_cache(page);
 		unlock_page(page);
 		page_cache_release(page);
+		page = NULL;
 	}
 
 	/*
@@ -539,7 +682,7 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
 	pgoff_t size, pgoff;
 	sector_t block, sector;
 	unsigned long pfn;
-	int result = 0;
+	int error, result = 0;
 
 	/* dax pmd mappings are broken wrt gup and fork */
 	if (!IS_ENABLED(CONFIG_FS_DAX_PMD))
@@ -651,6 +794,13 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
 		}
 
 		result |= vmf_insert_pfn_pmd(vma, address, pmd, pfn, write);
+
+		if (write) {
+			error = dax_radix_entry(mapping, pgoff, kaddr, true,
+					true);
+			if (error)
+				goto fallback;
+		}
 	}
 
  out:
@@ -702,15 +852,12 @@ EXPORT_SYMBOL_GPL(dax_pmd_fault);
  * dax_pfn_mkwrite - handle first write to DAX page
  * @vma: The virtual memory area where the fault occurred
  * @vmf: The description of the fault
- *
  */
 int dax_pfn_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
 {
-	struct super_block *sb = file_inode(vma->vm_file)->i_sb;
+	struct file *file = vma->vm_file;
 
-	sb_start_pagefault(sb);
-	file_update_time(vma->vm_file);
-	sb_end_pagefault(sb);
+	dax_radix_entry(file->f_mapping, vmf->pgoff, NULL, false, true);
 	return VM_FAULT_NOPAGE;
 }
 EXPORT_SYMBOL_GPL(dax_pfn_mkwrite);
diff --git a/include/linux/dax.h b/include/linux/dax.h
index e9d57f68..11eb183 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -41,4 +41,6 @@ static inline bool dax_mapping(struct address_space *mapping)
 {
 	return mapping->host && IS_DAX(mapping->host);
 }
+void dax_writeback_mapping_range(struct address_space *mapping, loff_t start,
+		loff_t end);
 #endif
diff --git a/mm/filemap.c b/mm/filemap.c
index 99dfbc9..9577783 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -482,6 +482,9 @@ int filemap_write_and_wait_range(struct address_space *mapping,
 {
 	int err = 0;
 
+	if (dax_mapping(mapping) && mapping->nrdax)
+		dax_writeback_mapping_range(mapping, lstart, lend);
+
 	if (mapping->nrpages) {
 		err = __filemap_fdatawrite_range(mapping, lstart, lend,
 						 WB_SYNC_ALL);
-- 
2.5.0

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[PATCH v5 4/7] dax: add support for fsync/sync

[Ross Zwisler]

To properly handle fsync/msync in an efficient way DAX needs to track dirty
pages so it is able to flush them durably to media on demand.

The tracking of dirty pages is done via the radix tree in struct
address_space.  This radix tree is already used by the page writeback
infrastructure for tracking dirty pages associated with an open file, and
it already has support for exceptional (non struct page*) entries.  We
build upon these features to add exceptional entries to the radix tree for
DAX dirty PMD or PTE pages at fault time.

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
---
 fs/dax.c            | 159 ++++++++++++++++++++++++++++++++++++++++++++++++++--
 include/linux/dax.h |   2 +
 mm/filemap.c        |   3 +
 3 files changed, 158 insertions(+), 6 deletions(-)

diff --git a/fs/dax.c b/fs/dax.c
index 43671b6..19347cf 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -24,6 +24,7 @@
 #include <linux/memcontrol.h>
 #include <linux/mm.h>
 #include <linux/mutex.h>
+#include <linux/pagevec.h>
 #include <linux/pmem.h>
 #include <linux/sched.h>
 #include <linux/uio.h>
@@ -289,6 +290,143 @@ static int copy_user_bh(struct page *to, struct buffer_head *bh,
 	return 0;
 }
 
+static int dax_radix_entry(struct address_space *mapping, pgoff_t index,
+		void __pmem *addr, bool pmd_entry, bool dirty)
+{
+	struct radix_tree_root *page_tree = &mapping->page_tree;
+	int error = 0;
+	void *entry;
+
+	__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
+
+	spin_lock_irq(&mapping->tree_lock);
+	entry = radix_tree_lookup(page_tree, index);
+
+	if (entry) {
+		if (!pmd_entry || RADIX_DAX_TYPE(entry) == RADIX_DAX_PMD)
+			goto dirty;
+		radix_tree_delete(&mapping->page_tree, index);
+		mapping->nrdax--;
+	}
+
+	if (!addr) {
+		/*
+		 * This can happen during correct operation if our pfn_mkwrite
+		 * fault raced against a hole punch operation.  If this
+		 * happens the pte that was hole punched will have been
+		 * unmapped and the radix tree entry will have been removed by
+		 * the time we are called, but the call will still happen.  We
+		 * will return all the way up to wp_pfn_shared(), where the
+		 * pte_same() check will fail, eventually causing page fault
+		 * to be retried by the CPU.
+		 */
+		goto unlock;
+	} else if (RADIX_DAX_TYPE(addr)) {
+		WARN_ONCE(1, "%s: invalid address %p\n", __func__, addr);
+		goto unlock;
+	}
+
+	error = radix_tree_insert(page_tree, index,
+			RADIX_DAX_ENTRY(addr, pmd_entry));
+	if (error)
+		goto unlock;
+
+	mapping->nrdax++;
+ dirty:
+	if (dirty)
+		radix_tree_tag_set(page_tree, index, PAGECACHE_TAG_DIRTY);
+ unlock:
+	spin_unlock_irq(&mapping->tree_lock);
+	return error;
+}
+
+static void dax_writeback_one(struct address_space *mapping, pgoff_t index,
+		void *entry)
+{
+	struct radix_tree_root *page_tree = &mapping->page_tree;
+	int type = RADIX_DAX_TYPE(entry);
+	struct radix_tree_node *node;
+	void **slot;
+
+	if (type != RADIX_DAX_PTE && type != RADIX_DAX_PMD) {
+		WARN_ON_ONCE(1);
+		return;
+	}
+
+	spin_lock_irq(&mapping->tree_lock);
+	/*
+	 * Regular page slots are stabilized by the page lock even
+	 * without the tree itself locked.  These unlocked entries
+	 * need verification under the tree lock.
+	 */
+	if (!__radix_tree_lookup(page_tree, index, &node, &slot))
+		goto unlock;
+	if (*slot != entry)
+		goto unlock;
+
+	/* another fsync thread may have already written back this entry */
+	if (!radix_tree_tag_get(page_tree, index, PAGECACHE_TAG_TOWRITE))
+		goto unlock;
+
+	radix_tree_tag_clear(page_tree, index, PAGECACHE_TAG_TOWRITE);
+
+	if (type == RADIX_DAX_PMD)
+		wb_cache_pmem(RADIX_DAX_ADDR(entry), PMD_SIZE);
+	else
+		wb_cache_pmem(RADIX_DAX_ADDR(entry), PAGE_SIZE);
+ unlock:
+	spin_unlock_irq(&mapping->tree_lock);
+}
+
+/*
+ * Flush the mapping to the persistent domain within the byte range of [start,
+ * end]. This is required by data integrity operations to ensure file data is
+ * on persistent storage prior to completion of the operation.
+ */
+void dax_writeback_mapping_range(struct address_space *mapping, loff_t start,
+		loff_t end)
+{
+	struct inode *inode = mapping->host;
+	pgoff_t indices[PAGEVEC_SIZE];
+	pgoff_t start_page, end_page;
+	struct pagevec pvec;
+	void *entry;
+	int i;
+
+	if (inode->i_blkbits != PAGE_SHIFT) {
+		WARN_ON_ONCE(1);
+		return;
+	}
+
+	rcu_read_lock();
+	entry = radix_tree_lookup(&mapping->page_tree, start & PMD_MASK);
+	rcu_read_unlock();
+
+	/* see if the start of our range is covered by a PMD entry */
+	if (entry && RADIX_DAX_TYPE(entry) == RADIX_DAX_PMD)
+		start &= PMD_MASK;
+
+	start_page = start >> PAGE_CACHE_SHIFT;
+	end_page = end >> PAGE_CACHE_SHIFT;
+
+	tag_pages_for_writeback(mapping, start_page, end_page);
+
+	pagevec_init(&pvec, 0);
+	while (1) {
+		pvec.nr = find_get_entries_tag(mapping, start_page,
+				PAGECACHE_TAG_TOWRITE, PAGEVEC_SIZE,
+				pvec.pages, indices);
+
+		if (pvec.nr == 0)
+			break;
+
+		for (i = 0; i < pvec.nr; i++)
+			dax_writeback_one(mapping, indices[i], pvec.pages[i]);
+	}
+	wmb_pmem();
+}
+EXPORT_SYMBOL_GPL(dax_writeback_mapping_range);
+
 static int dax_insert_mapping(struct inode *inode, struct buffer_head *bh,
 			struct vm_area_struct *vma, struct vm_fault *vmf)
 {
@@ -329,7 +467,11 @@ static int dax_insert_mapping(struct inode *inode, struct buffer_head *bh,
 	}
 
 	error = vm_insert_mixed(vma, vaddr, pfn);
+	if (error)
+		goto out;
 
+	error = dax_radix_entry(mapping, vmf->pgoff, addr, false,
+			vmf->flags & FAULT_FLAG_WRITE);
  out:
 	i_mmap_unlock_read(mapping);
 
@@ -452,6 +594,7 @@ int __dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
 		delete_from_page_cache(page);
 		unlock_page(page);
 		page_cache_release(page);
+		page = NULL;
 	}
 
 	/*
@@ -539,7 +682,7 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
 	pgoff_t size, pgoff;
 	sector_t block, sector;
 	unsigned long pfn;
-	int result = 0;
+	int error, result = 0;
 
 	/* dax pmd mappings are broken wrt gup and fork */
 	if (!IS_ENABLED(CONFIG_FS_DAX_PMD))
@@ -651,6 +794,13 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
 		}
 
 		result |= vmf_insert_pfn_pmd(vma, address, pmd, pfn, write);
+
+		if (write) {
+			error = dax_radix_entry(mapping, pgoff, kaddr, true,
+					true);
+			if (error)
+				goto fallback;
+		}
 	}
 
  out:
@@ -702,15 +852,12 @@ EXPORT_SYMBOL_GPL(dax_pmd_fault);
  * dax_pfn_mkwrite - handle first write to DAX page
  * @vma: The virtual memory area where the fault occurred
  * @vmf: The description of the fault
- *
  */
 int dax_pfn_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
 {
-	struct super_block *sb = file_inode(vma->vm_file)->i_sb;
+	struct file *file = vma->vm_file;
 
-	sb_start_pagefault(sb);
-	file_update_time(vma->vm_file);
-	sb_end_pagefault(sb);
+	dax_radix_entry(file->f_mapping, vmf->pgoff, NULL, false, true);
 	return VM_FAULT_NOPAGE;
 }
 EXPORT_SYMBOL_GPL(dax_pfn_mkwrite);
diff --git a/include/linux/dax.h b/include/linux/dax.h
index e9d57f68..11eb183 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -41,4 +41,6 @@ static inline bool dax_mapping(struct address_space *mapping)
 {
 	return mapping->host && IS_DAX(mapping->host);
 }
+void dax_writeback_mapping_range(struct address_space *mapping, loff_t start,
+		loff_t end);
 #endif
diff --git a/mm/filemap.c b/mm/filemap.c
index 99dfbc9..9577783 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -482,6 +482,9 @@ int filemap_write_and_wait_range(struct address_space *mapping,
 {
 	int err = 0;
 
+	if (dax_mapping(mapping) && mapping->nrdax)
+		dax_writeback_mapping_range(mapping, lstart, lend);
+
 	if (mapping->nrpages) {
 		err = __filemap_fdatawrite_range(mapping, lstart, lend,
 						 WB_SYNC_ALL);
-- 
2.5.0

[PATCH v5 4/7] dax: add support for fsync/sync

[Ross Zwisler]

To properly handle fsync/msync in an efficient way DAX needs to track dirty
pages so it is able to flush them durably to media on demand.

The tracking of dirty pages is done via the radix tree in struct
address_space.  This radix tree is already used by the page writeback
infrastructure for tracking dirty pages associated with an open file, and
it already has support for exceptional (non struct page*) entries.  We
build upon these features to add exceptional entries to the radix tree for
DAX dirty PMD or PTE pages at fault time.

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
---
 fs/dax.c            | 159 ++++++++++++++++++++++++++++++++++++++++++++++++++--
 include/linux/dax.h |   2 +
 mm/filemap.c        |   3 +
 3 files changed, 158 insertions(+), 6 deletions(-)

diff --git a/fs/dax.c b/fs/dax.c
index 43671b6..19347cf 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -24,6 +24,7 @@
 #include <linux/memcontrol.h>
 #include <linux/mm.h>
 #include <linux/mutex.h>
+#include <linux/pagevec.h>
 #include <linux/pmem.h>
 #include <linux/sched.h>
 #include <linux/uio.h>
@@ -289,6 +290,143 @@ static int copy_user_bh(struct page *to, struct buffer_head *bh,
 	return 0;
 }
 
+static int dax_radix_entry(struct address_space *mapping, pgoff_t index,
+		void __pmem *addr, bool pmd_entry, bool dirty)
+{
+	struct radix_tree_root *page_tree = &mapping->page_tree;
+	int error = 0;
+	void *entry;
+
+	__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
+
+	spin_lock_irq(&mapping->tree_lock);
+	entry = radix_tree_lookup(page_tree, index);
+
+	if (entry) {
+		if (!pmd_entry || RADIX_DAX_TYPE(entry) == RADIX_DAX_PMD)
+			goto dirty;
+		radix_tree_delete(&mapping->page_tree, index);
+		mapping->nrdax--;
+	}
+
+	if (!addr) {
+		/*
+		 * This can happen during correct operation if our pfn_mkwrite
+		 * fault raced against a hole punch operation.  If this
+		 * happens the pte that was hole punched will have been
+		 * unmapped and the radix tree entry will have been removed by
+		 * the time we are called, but the call will still happen.  We
+		 * will return all the way up to wp_pfn_shared(), where the
+		 * pte_same() check will fail, eventually causing page fault
+		 * to be retried by the CPU.
+		 */
+		goto unlock;
+	} else if (RADIX_DAX_TYPE(addr)) {
+		WARN_ONCE(1, "%s: invalid address %p\n", __func__, addr);
+		goto unlock;
+	}
+
+	error = radix_tree_insert(page_tree, index,
+			RADIX_DAX_ENTRY(addr, pmd_entry));
+	if (error)
+		goto unlock;
+
+	mapping->nrdax++;
+ dirty:
+	if (dirty)
+		radix_tree_tag_set(page_tree, index, PAGECACHE_TAG_DIRTY);
+ unlock:
+	spin_unlock_irq(&mapping->tree_lock);
+	return error;
+}
+
+static void dax_writeback_one(struct address_space *mapping, pgoff_t index,
+		void *entry)
+{
+	struct radix_tree_root *page_tree = &mapping->page_tree;
+	int type = RADIX_DAX_TYPE(entry);
+	struct radix_tree_node *node;
+	void **slot;
+
+	if (type != RADIX_DAX_PTE && type != RADIX_DAX_PMD) {
+		WARN_ON_ONCE(1);
+		return;
+	}
+
+	spin_lock_irq(&mapping->tree_lock);
+	/*
+	 * Regular page slots are stabilized by the page lock even
+	 * without the tree itself locked.  These unlocked entries
+	 * need verification under the tree lock.
+	 */
+	if (!__radix_tree_lookup(page_tree, index, &node, &slot))
+		goto unlock;
+	if (*slot != entry)
+		goto unlock;
+
+	/* another fsync thread may have already written back this entry */
+	if (!radix_tree_tag_get(page_tree, index, PAGECACHE_TAG_TOWRITE))
+		goto unlock;
+
+	radix_tree_tag_clear(page_tree, index, PAGECACHE_TAG_TOWRITE);
+
+	if (type == RADIX_DAX_PMD)
+		wb_cache_pmem(RADIX_DAX_ADDR(entry), PMD_SIZE);
+	else
+		wb_cache_pmem(RADIX_DAX_ADDR(entry), PAGE_SIZE);
+ unlock:
+	spin_unlock_irq(&mapping->tree_lock);
+}
+
+/*
+ * Flush the mapping to the persistent domain within the byte range of [start,
+ * end]. This is required by data integrity operations to ensure file data is
+ * on persistent storage prior to completion of the operation.
+ */
+void dax_writeback_mapping_range(struct address_space *mapping, loff_t start,
+		loff_t end)
+{
+	struct inode *inode = mapping->host;
+	pgoff_t indices[PAGEVEC_SIZE];
+	pgoff_t start_page, end_page;
+	struct pagevec pvec;
+	void *entry;
+	int i;
+
+	if (inode->i_blkbits != PAGE_SHIFT) {
+		WARN_ON_ONCE(1);
+		return;
+	}
+
+	rcu_read_lock();
+	entry = radix_tree_lookup(&mapping->page_tree, start & PMD_MASK);
+	rcu_read_unlock();
+
+	/* see if the start of our range is covered by a PMD entry */
+	if (entry && RADIX_DAX_TYPE(entry) == RADIX_DAX_PMD)
+		start &= PMD_MASK;
+
+	start_page = start >> PAGE_CACHE_SHIFT;
+	end_page = end >> PAGE_CACHE_SHIFT;
+
+	tag_pages_for_writeback(mapping, start_page, end_page);
+
+	pagevec_init(&pvec, 0);
+	while (1) {
+		pvec.nr = find_get_entries_tag(mapping, start_page,
+				PAGECACHE_TAG_TOWRITE, PAGEVEC_SIZE,
+				pvec.pages, indices);
+
+		if (pvec.nr == 0)
+			break;
+
+		for (i = 0; i < pvec.nr; i++)
+			dax_writeback_one(mapping, indices[i], pvec.pages[i]);
+	}
+	wmb_pmem();
+}
+EXPORT_SYMBOL_GPL(dax_writeback_mapping_range);
+
 static int dax_insert_mapping(struct inode *inode, struct buffer_head *bh,
 			struct vm_area_struct *vma, struct vm_fault *vmf)
 {
@@ -329,7 +467,11 @@ static int dax_insert_mapping(struct inode *inode, struct buffer_head *bh,
 	}
 
 	error = vm_insert_mixed(vma, vaddr, pfn);
+	if (error)
+		goto out;
 
+	error = dax_radix_entry(mapping, vmf->pgoff, addr, false,
+			vmf->flags & FAULT_FLAG_WRITE);
  out:
 	i_mmap_unlock_read(mapping);
 
@@ -452,6 +594,7 @@ int __dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
 		delete_from_page_cache(page);
 		unlock_page(page);
 		page_cache_release(page);
+		page = NULL;
 	}
 
 	/*
@@ -539,7 +682,7 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
 	pgoff_t size, pgoff;
 	sector_t block, sector;
 	unsigned long pfn;
-	int result = 0;
+	int error, result = 0;
 
 	/* dax pmd mappings are broken wrt gup and fork */
 	if (!IS_ENABLED(CONFIG_FS_DAX_PMD))
@@ -651,6 +794,13 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
 		}
 
 		result |= vmf_insert_pfn_pmd(vma, address, pmd, pfn, write);
+
+		if (write) {
+			error = dax_radix_entry(mapping, pgoff, kaddr, true,
+					true);
+			if (error)
+				goto fallback;
+		}
 	}
 
  out:
@@ -702,15 +852,12 @@ EXPORT_SYMBOL_GPL(dax_pmd_fault);
  * dax_pfn_mkwrite - handle first write to DAX page
  * @vma: The virtual memory area where the fault occurred
  * @vmf: The description of the fault
- *
  */
 int dax_pfn_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
 {
-	struct super_block *sb = file_inode(vma->vm_file)->i_sb;
+	struct file *file = vma->vm_file;
 
-	sb_start_pagefault(sb);
-	file_update_time(vma->vm_file);
-	sb_end_pagefault(sb);
+	dax_radix_entry(file->f_mapping, vmf->pgoff, NULL, false, true);
 	return VM_FAULT_NOPAGE;
 }
 EXPORT_SYMBOL_GPL(dax_pfn_mkwrite);
diff --git a/include/linux/dax.h b/include/linux/dax.h
index e9d57f68..11eb183 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -41,4 +41,6 @@ static inline bool dax_mapping(struct address_space *mapping)
 {
 	return mapping->host && IS_DAX(mapping->host);
 }
+void dax_writeback_mapping_range(struct address_space *mapping, loff_t start,
+		loff_t end);
 #endif
diff --git a/mm/filemap.c b/mm/filemap.c
index 99dfbc9..9577783 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -482,6 +482,9 @@ int filemap_write_and_wait_range(struct address_space *mapping,
 {
 	int err = 0;
 
+	if (dax_mapping(mapping) && mapping->nrdax)
+		dax_writeback_mapping_range(mapping, lstart, lend);
+
 	if (mapping->nrpages) {
 		err = __filemap_fdatawrite_range(mapping, lstart, lend,
 						 WB_SYNC_ALL);
-- 
2.5.0

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[PATCH v5 5/7] ext2: call dax_pfn_mkwrite() for DAX fsync/msync

[Ross Zwisler]

To properly support the new DAX fsync/msync infrastructure filesystems
need to call dax_pfn_mkwrite() so that DAX can track when user pages are
dirtied.

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
---
 fs/ext2/file.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/ext2/file.c b/fs/ext2/file.c
index 11a42c5..2c88d68 100644
--- a/fs/ext2/file.c
+++ b/fs/ext2/file.c
@@ -102,8 +102,8 @@ static int ext2_dax_pfn_mkwrite(struct vm_area_struct *vma,
 {
 	struct inode *inode = file_inode(vma->vm_file);
 	struct ext2_inode_info *ei = EXT2_I(inode);
-	int ret = VM_FAULT_NOPAGE;
 	loff_t size;
+	int ret;
 
 	sb_start_pagefault(inode->i_sb);
 	file_update_time(vma->vm_file);
@@ -113,6 +113,8 @@ static int ext2_dax_pfn_mkwrite(struct vm_area_struct *vma,
 	size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
 	if (vmf->pgoff >= size)
 		ret = VM_FAULT_SIGBUS;
+	else
+		ret = dax_pfn_mkwrite(vma, vmf);
 
 	up_read(&ei->dax_sem);
 	sb_end_pagefault(inode->i_sb);
-- 
2.5.0

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[PATCH v5 5/7] ext2: call dax_pfn_mkwrite() for DAX fsync/msync

[Ross Zwisler]

To properly support the new DAX fsync/msync infrastructure filesystems
need to call dax_pfn_mkwrite() so that DAX can track when user pages are
dirtied.

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
---
 fs/ext2/file.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/ext2/file.c b/fs/ext2/file.c
index 11a42c5..2c88d68 100644
--- a/fs/ext2/file.c
+++ b/fs/ext2/file.c
@@ -102,8 +102,8 @@ static int ext2_dax_pfn_mkwrite(struct vm_area_struct *vma,
 {
 	struct inode *inode = file_inode(vma->vm_file);
 	struct ext2_inode_info *ei = EXT2_I(inode);
-	int ret = VM_FAULT_NOPAGE;
 	loff_t size;
+	int ret;
 
 	sb_start_pagefault(inode->i_sb);
 	file_update_time(vma->vm_file);
@@ -113,6 +113,8 @@ static int ext2_dax_pfn_mkwrite(struct vm_area_struct *vma,
 	size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
 	if (vmf->pgoff >= size)
 		ret = VM_FAULT_SIGBUS;
+	else
+		ret = dax_pfn_mkwrite(vma, vmf);
 
 	up_read(&ei->dax_sem);
 	sb_end_pagefault(inode->i_sb);
-- 
2.5.0

[PATCH v5 5/7] ext2: call dax_pfn_mkwrite() for DAX fsync/msync

[Ross Zwisler]

To properly support the new DAX fsync/msync infrastructure filesystems
need to call dax_pfn_mkwrite() so that DAX can track when user pages are
dirtied.

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
---
 fs/ext2/file.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/ext2/file.c b/fs/ext2/file.c
index 11a42c5..2c88d68 100644
--- a/fs/ext2/file.c
+++ b/fs/ext2/file.c
@@ -102,8 +102,8 @@ static int ext2_dax_pfn_mkwrite(struct vm_area_struct *vma,
 {
 	struct inode *inode = file_inode(vma->vm_file);
 	struct ext2_inode_info *ei = EXT2_I(inode);
-	int ret = VM_FAULT_NOPAGE;
 	loff_t size;
+	int ret;
 
 	sb_start_pagefault(inode->i_sb);
 	file_update_time(vma->vm_file);
@@ -113,6 +113,8 @@ static int ext2_dax_pfn_mkwrite(struct vm_area_struct *vma,
 	size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
 	if (vmf->pgoff >= size)
 		ret = VM_FAULT_SIGBUS;
+	else
+		ret = dax_pfn_mkwrite(vma, vmf);
 
 	up_read(&ei->dax_sem);
 	sb_end_pagefault(inode->i_sb);
-- 
2.5.0

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[PATCH v5 6/7] ext4: call dax_pfn_mkwrite() for DAX fsync/msync

[Ross Zwisler]

To properly support the new DAX fsync/msync infrastructure filesystems
need to call dax_pfn_mkwrite() so that DAX can track when user pages are
dirtied.

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
---
 fs/ext4/file.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/ext4/file.c b/fs/ext4/file.c
index 749b222..8c8965c 100644
--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -291,8 +291,8 @@ static int ext4_dax_pfn_mkwrite(struct vm_area_struct *vma,
 {
 	struct inode *inode = file_inode(vma->vm_file);
 	struct super_block *sb = inode->i_sb;
-	int ret = VM_FAULT_NOPAGE;
 	loff_t size;
+	int ret;
 
 	sb_start_pagefault(sb);
 	file_update_time(vma->vm_file);
@@ -300,6 +300,8 @@ static int ext4_dax_pfn_mkwrite(struct vm_area_struct *vma,
 	size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
 	if (vmf->pgoff >= size)
 		ret = VM_FAULT_SIGBUS;
+	else
+		ret = dax_pfn_mkwrite(vma, vmf);
 	up_read(&EXT4_I(inode)->i_mmap_sem);
 	sb_end_pagefault(sb);
 
-- 
2.5.0

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[PATCH v5 6/7] ext4: call dax_pfn_mkwrite() for DAX fsync/msync

[Ross Zwisler]

To properly support the new DAX fsync/msync infrastructure filesystems
need to call dax_pfn_mkwrite() so that DAX can track when user pages are
dirtied.

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
---
 fs/ext4/file.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/ext4/file.c b/fs/ext4/file.c
index 749b222..8c8965c 100644
--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -291,8 +291,8 @@ static int ext4_dax_pfn_mkwrite(struct vm_area_struct *vma,
 {
 	struct inode *inode = file_inode(vma->vm_file);
 	struct super_block *sb = inode->i_sb;
-	int ret = VM_FAULT_NOPAGE;
 	loff_t size;
+	int ret;
 
 	sb_start_pagefault(sb);
 	file_update_time(vma->vm_file);
@@ -300,6 +300,8 @@ static int ext4_dax_pfn_mkwrite(struct vm_area_struct *vma,
 	size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
 	if (vmf->pgoff >= size)
 		ret = VM_FAULT_SIGBUS;
+	else
+		ret = dax_pfn_mkwrite(vma, vmf);
 	up_read(&EXT4_I(inode)->i_mmap_sem);
 	sb_end_pagefault(sb);
 
-- 
2.5.0

[PATCH v5 6/7] ext4: call dax_pfn_mkwrite() for DAX fsync/msync

[Ross Zwisler]

To properly support the new DAX fsync/msync infrastructure filesystems
need to call dax_pfn_mkwrite() so that DAX can track when user pages are
dirtied.

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
---
 fs/ext4/file.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/ext4/file.c b/fs/ext4/file.c
index 749b222..8c8965c 100644
--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -291,8 +291,8 @@ static int ext4_dax_pfn_mkwrite(struct vm_area_struct *vma,
 {
 	struct inode *inode = file_inode(vma->vm_file);
 	struct super_block *sb = inode->i_sb;
-	int ret = VM_FAULT_NOPAGE;
 	loff_t size;
+	int ret;
 
 	sb_start_pagefault(sb);
 	file_update_time(vma->vm_file);
@@ -300,6 +300,8 @@ static int ext4_dax_pfn_mkwrite(struct vm_area_struct *vma,
 	size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
 	if (vmf->pgoff >= size)
 		ret = VM_FAULT_SIGBUS;
+	else
+		ret = dax_pfn_mkwrite(vma, vmf);
 	up_read(&EXT4_I(inode)->i_mmap_sem);
 	sb_end_pagefault(sb);
 
-- 
2.5.0

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[PATCH v5 7/7] xfs: call dax_pfn_mkwrite() for DAX fsync/msync

[Ross Zwisler]

To properly support the new DAX fsync/msync infrastructure filesystems
need to call dax_pfn_mkwrite() so that DAX can track when user pages are
dirtied.

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
---
 fs/xfs/xfs_file.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index f5392ab..40ffbb1 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -1603,9 +1603,8 @@ xfs_filemap_pmd_fault(
 /*
  * pfn_mkwrite was originally inteneded to ensure we capture time stamp
  * updates on write faults. In reality, it's need to serialise against
- * truncate similar to page_mkwrite. Hence we open-code dax_pfn_mkwrite()
- * here and cycle the XFS_MMAPLOCK_SHARED to ensure we serialise the fault
- * barrier in place.
+ * truncate similar to page_mkwrite. Hence we cycle the XFS_MMAPLOCK_SHARED
+ * to ensure we serialise the fault barrier in place.
  */
 static int
 xfs_filemap_pfn_mkwrite(
@@ -1628,6 +1627,8 @@ xfs_filemap_pfn_mkwrite(
 	size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
 	if (vmf->pgoff >= size)
 		ret = VM_FAULT_SIGBUS;
+	else if (IS_DAX(inode))
+		ret = dax_pfn_mkwrite(vma, vmf);
 	xfs_iunlock(ip, XFS_MMAPLOCK_SHARED);
 	sb_end_pagefault(inode->i_sb);
 	return ret;
-- 
2.5.0

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[PATCH v5 7/7] xfs: call dax_pfn_mkwrite() for DAX fsync/msync

[Ross Zwisler]

To properly support the new DAX fsync/msync infrastructure filesystems
need to call dax_pfn_mkwrite() so that DAX can track when user pages are
dirtied.

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
---
 fs/xfs/xfs_file.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index f5392ab..40ffbb1 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -1603,9 +1603,8 @@ xfs_filemap_pmd_fault(
 /*
  * pfn_mkwrite was originally inteneded to ensure we capture time stamp
  * updates on write faults. In reality, it's need to serialise against
- * truncate similar to page_mkwrite. Hence we open-code dax_pfn_mkwrite()
- * here and cycle the XFS_MMAPLOCK_SHARED to ensure we serialise the fault
- * barrier in place.
+ * truncate similar to page_mkwrite. Hence we cycle the XFS_MMAPLOCK_SHARED
+ * to ensure we serialise the fault barrier in place.
  */
 static int
 xfs_filemap_pfn_mkwrite(
@@ -1628,6 +1627,8 @@ xfs_filemap_pfn_mkwrite(
 	size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
 	if (vmf->pgoff >= size)
 		ret = VM_FAULT_SIGBUS;
+	else if (IS_DAX(inode))
+		ret = dax_pfn_mkwrite(vma, vmf);
 	xfs_iunlock(ip, XFS_MMAPLOCK_SHARED);
 	sb_end_pagefault(inode->i_sb);
 	return ret;
-- 
2.5.0

[PATCH v5 7/7] xfs: call dax_pfn_mkwrite() for DAX fsync/msync

[Ross Zwisler]

To properly support the new DAX fsync/msync infrastructure filesystems
need to call dax_pfn_mkwrite() so that DAX can track when user pages are
dirtied.

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
---
 fs/xfs/xfs_file.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index f5392ab..40ffbb1 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -1603,9 +1603,8 @@ xfs_filemap_pmd_fault(
 /*
  * pfn_mkwrite was originally inteneded to ensure we capture time stamp
  * updates on write faults. In reality, it's need to serialise against
- * truncate similar to page_mkwrite. Hence we open-code dax_pfn_mkwrite()
- * here and cycle the XFS_MMAPLOCK_SHARED to ensure we serialise the fault
- * barrier in place.
+ * truncate similar to page_mkwrite. Hence we cycle the XFS_MMAPLOCK_SHARED
+ * to ensure we serialise the fault barrier in place.
  */
 static int
 xfs_filemap_pfn_mkwrite(
@@ -1628,6 +1627,8 @@ xfs_filemap_pfn_mkwrite(
 	size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
 	if (vmf->pgoff >= size)
 		ret = VM_FAULT_SIGBUS;
+	else if (IS_DAX(inode))
+		ret = dax_pfn_mkwrite(vma, vmf);
 	xfs_iunlock(ip, XFS_MMAPLOCK_SHARED);
 	sb_end_pagefault(inode->i_sb);
 	return ret;
-- 
2.5.0

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Re: [PATCH v5 4/7] dax: add support for fsync/sync

[Dan Williams]

On Fri, Dec 18, 2015 at 9:22 PM, Ross Zwisler
<ross.zwisler@linux.intel.com> wrote:
> To properly handle fsync/msync in an efficient way DAX needs to track dirty
> pages so it is able to flush them durably to media on demand.
>
> The tracking of dirty pages is done via the radix tree in struct
> address_space.  This radix tree is already used by the page writeback
> infrastructure for tracking dirty pages associated with an open file, and
> it already has support for exceptional (non struct page*) entries.  We
> build upon these features to add exceptional entries to the radix tree for
> DAX dirty PMD or PTE pages at fault time.
>
> Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
[..]
> +static void dax_writeback_one(struct address_space *mapping, pgoff_t index,
> +               void *entry)
> +{
> +       struct radix_tree_root *page_tree = &mapping->page_tree;
> +       int type = RADIX_DAX_TYPE(entry);
> +       struct radix_tree_node *node;
> +       void **slot;
> +
> +       if (type != RADIX_DAX_PTE && type != RADIX_DAX_PMD) {
> +               WARN_ON_ONCE(1);
> +               return;
> +       }
> +
> +       spin_lock_irq(&mapping->tree_lock);
> +       /*
> +        * Regular page slots are stabilized by the page lock even
> +        * without the tree itself locked.  These unlocked entries
> +        * need verification under the tree lock.
> +        */
> +       if (!__radix_tree_lookup(page_tree, index, &node, &slot))
> +               goto unlock;
> +       if (*slot != entry)
> +               goto unlock;
> +
> +       /* another fsync thread may have already written back this entry */
> +       if (!radix_tree_tag_get(page_tree, index, PAGECACHE_TAG_TOWRITE))
> +               goto unlock;
> +
> +       radix_tree_tag_clear(page_tree, index, PAGECACHE_TAG_TOWRITE);
> +
> +       if (type == RADIX_DAX_PMD)
> +               wb_cache_pmem(RADIX_DAX_ADDR(entry), PMD_SIZE);
> +       else
> +               wb_cache_pmem(RADIX_DAX_ADDR(entry), PAGE_SIZE);

Hi Ross, I should have realized this sooner, but what guarantees that
the address returned by RADIX_DAX_ADDR(entry) is still valid at this
point?  I think we need to store the sector in the radix tree and then
perform a new dax_map_atomic() operation to either lookup a valid
address or fail the sync request.  Otherwise, if the device is gone
we'll crash, or write into some other random vmalloc address space.

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Re: [PATCH v5 4/7] dax: add support for fsync/sync

[Dan Williams]

On Fri, Dec 18, 2015 at 9:22 PM, Ross Zwisler
<ross.zwisler@linux.intel.com> wrote:
> To properly handle fsync/msync in an efficient way DAX needs to track dirty
> pages so it is able to flush them durably to media on demand.
>
> The tracking of dirty pages is done via the radix tree in struct
> address_space.  This radix tree is already used by the page writeback
> infrastructure for tracking dirty pages associated with an open file, and
> it already has support for exceptional (non struct page*) entries.  We
> build upon these features to add exceptional entries to the radix tree for
> DAX dirty PMD or PTE pages at fault time.
>
> Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
[..]
> +static void dax_writeback_one(struct address_space *mapping, pgoff_t index,
> +               void *entry)
> +{
> +       struct radix_tree_root *page_tree = &mapping->page_tree;
> +       int type = RADIX_DAX_TYPE(entry);
> +       struct radix_tree_node *node;
> +       void **slot;
> +
> +       if (type != RADIX_DAX_PTE && type != RADIX_DAX_PMD) {
> +               WARN_ON_ONCE(1);
> +               return;
> +       }
> +
> +       spin_lock_irq(&mapping->tree_lock);
> +       /*
> +        * Regular page slots are stabilized by the page lock even
> +        * without the tree itself locked.  These unlocked entries
> +        * need verification under the tree lock.
> +        */
> +       if (!__radix_tree_lookup(page_tree, index, &node, &slot))
> +               goto unlock;
> +       if (*slot != entry)
> +               goto unlock;
> +
> +       /* another fsync thread may have already written back this entry */
> +       if (!radix_tree_tag_get(page_tree, index, PAGECACHE_TAG_TOWRITE))
> +               goto unlock;
> +
> +       radix_tree_tag_clear(page_tree, index, PAGECACHE_TAG_TOWRITE);
> +
> +       if (type == RADIX_DAX_PMD)
> +               wb_cache_pmem(RADIX_DAX_ADDR(entry), PMD_SIZE);
> +       else
> +               wb_cache_pmem(RADIX_DAX_ADDR(entry), PAGE_SIZE);

Hi Ross, I should have realized this sooner, but what guarantees that
the address returned by RADIX_DAX_ADDR(entry) is still valid at this
point?  I think we need to store the sector in the radix tree and then
perform a new dax_map_atomic() operation to either lookup a valid
address or fail the sync request.  Otherwise, if the device is gone
we'll crash, or write into some other random vmalloc address space.

Re: [PATCH v5 4/7] dax: add support for fsync/sync

[Dan Williams]

On Fri, Dec 18, 2015 at 9:22 PM, Ross Zwisler
<ross.zwisler@linux.intel.com> wrote:
> To properly handle fsync/msync in an efficient way DAX needs to track dirty
> pages so it is able to flush them durably to media on demand.
>
> The tracking of dirty pages is done via the radix tree in struct
> address_space.  This radix tree is already used by the page writeback
> infrastructure for tracking dirty pages associated with an open file, and
> it already has support for exceptional (non struct page*) entries.  We
> build upon these features to add exceptional entries to the radix tree for
> DAX dirty PMD or PTE pages at fault time.
>
> Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
[..]
> +static void dax_writeback_one(struct address_space *mapping, pgoff_t index,
> +               void *entry)
> +{
> +       struct radix_tree_root *page_tree = &mapping->page_tree;
> +       int type = RADIX_DAX_TYPE(entry);
> +       struct radix_tree_node *node;
> +       void **slot;
> +
> +       if (type != RADIX_DAX_PTE && type != RADIX_DAX_PMD) {
> +               WARN_ON_ONCE(1);
> +               return;
> +       }
> +
> +       spin_lock_irq(&mapping->tree_lock);
> +       /*
> +        * Regular page slots are stabilized by the page lock even
> +        * without the tree itself locked.  These unlocked entries
> +        * need verification under the tree lock.
> +        */
> +       if (!__radix_tree_lookup(page_tree, index, &node, &slot))
> +               goto unlock;
> +       if (*slot != entry)
> +               goto unlock;
> +
> +       /* another fsync thread may have already written back this entry */
> +       if (!radix_tree_tag_get(page_tree, index, PAGECACHE_TAG_TOWRITE))
> +               goto unlock;
> +
> +       radix_tree_tag_clear(page_tree, index, PAGECACHE_TAG_TOWRITE);
> +
> +       if (type == RADIX_DAX_PMD)
> +               wb_cache_pmem(RADIX_DAX_ADDR(entry), PMD_SIZE);
> +       else
> +               wb_cache_pmem(RADIX_DAX_ADDR(entry), PAGE_SIZE);

Hi Ross, I should have realized this sooner, but what guarantees that
the address returned by RADIX_DAX_ADDR(entry) is still valid at this
point?  I think we need to store the sector in the radix tree and then
perform a new dax_map_atomic() operation to either lookup a valid
address or fail the sync request.  Otherwise, if the device is gone
we'll crash, or write into some other random vmalloc address space.

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Re: [PATCH v5 4/7] dax: add support for fsync/sync

[Ross Zwisler]

On Sat, Dec 19, 2015 at 10:37:46AM -0800, Dan Williams wrote:
> On Fri, Dec 18, 2015 at 9:22 PM, Ross Zwisler
> <ross.zwisler@linux.intel.com> wrote:
> > To properly handle fsync/msync in an efficient way DAX needs to track dirty
> > pages so it is able to flush them durably to media on demand.
> >
> > The tracking of dirty pages is done via the radix tree in struct
> > address_space.  This radix tree is already used by the page writeback
> > infrastructure for tracking dirty pages associated with an open file, and
> > it already has support for exceptional (non struct page*) entries.  We
> > build upon these features to add exceptional entries to the radix tree for
> > DAX dirty PMD or PTE pages at fault time.
> >
> > Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
> [..]
> > +static void dax_writeback_one(struct address_space *mapping, pgoff_t index,
> > +               void *entry)
> > +{
> > +       struct radix_tree_root *page_tree = &mapping->page_tree;
> > +       int type = RADIX_DAX_TYPE(entry);
> > +       struct radix_tree_node *node;
> > +       void **slot;
> > +
> > +       if (type != RADIX_DAX_PTE && type != RADIX_DAX_PMD) {
> > +               WARN_ON_ONCE(1);
> > +               return;
> > +       }
> > +
> > +       spin_lock_irq(&mapping->tree_lock);
> > +       /*
> > +        * Regular page slots are stabilized by the page lock even
> > +        * without the tree itself locked.  These unlocked entries
> > +        * need verification under the tree lock.
> > +        */
> > +       if (!__radix_tree_lookup(page_tree, index, &node, &slot))
> > +               goto unlock;
> > +       if (*slot != entry)
> > +               goto unlock;
> > +
> > +       /* another fsync thread may have already written back this entry */
> > +       if (!radix_tree_tag_get(page_tree, index, PAGECACHE_TAG_TOWRITE))
> > +               goto unlock;
> > +
> > +       radix_tree_tag_clear(page_tree, index, PAGECACHE_TAG_TOWRITE);
> > +
> > +       if (type == RADIX_DAX_PMD)
> > +               wb_cache_pmem(RADIX_DAX_ADDR(entry), PMD_SIZE);
> > +       else
> > +               wb_cache_pmem(RADIX_DAX_ADDR(entry), PAGE_SIZE);
> 
> Hi Ross, I should have realized this sooner, but what guarantees that
> the address returned by RADIX_DAX_ADDR(entry) is still valid at this
> point?  I think we need to store the sector in the radix tree and then
> perform a new dax_map_atomic() operation to either lookup a valid
> address or fail the sync request.  Otherwise, if the device is gone
> we'll crash, or write into some other random vmalloc address space.

Ah, good point, thank you.  v4 of this series is based on a version of
DAX where we aren't properly dealing with PMEM device removal.  I've got an
updated version that merges with your dax_map_atomic() changes, and I'll add
this change into v5 which I will send out today.  Thank you for the
suggestion.

One clarification, with the code as it is in v4 we are only doing
clflush/clflushopt/clwb instructions on the kaddr we've stored in the radix
tree, so I don't think that there is actually a risk of us doing a "write into
some other random vmalloc address space"?  I think at worse we will end up
clflushing an address that either isn't mapped or has been remapped by someone
else.  Or are you worried that the clflush would trigger a cache writeback to
a memory address where writes have side effects, thus triggering the side
effect?

I definitely think it needs to be fixed, I'm just trying to make sure I
understood your comment.

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Re: [PATCH v5 4/7] dax: add support for fsync/sync

[Ross Zwisler]

On Sat, Dec 19, 2015 at 10:37:46AM -0800, Dan Williams wrote:
> On Fri, Dec 18, 2015 at 9:22 PM, Ross Zwisler
> <ross.zwisler@linux.intel.com> wrote:
> > To properly handle fsync/msync in an efficient way DAX needs to track dirty
> > pages so it is able to flush them durably to media on demand.
> >
> > The tracking of dirty pages is done via the radix tree in struct
> > address_space.  This radix tree is already used by the page writeback
> > infrastructure for tracking dirty pages associated with an open file, and
> > it already has support for exceptional (non struct page*) entries.  We
> > build upon these features to add exceptional entries to the radix tree for
> > DAX dirty PMD or PTE pages at fault time.
> >
> > Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
> [..]
> > +static void dax_writeback_one(struct address_space *mapping, pgoff_t index,
> > +               void *entry)
> > +{
> > +       struct radix_tree_root *page_tree = &mapping->page_tree;
> > +       int type = RADIX_DAX_TYPE(entry);
> > +       struct radix_tree_node *node;
> > +       void **slot;
> > +
> > +       if (type != RADIX_DAX_PTE && type != RADIX_DAX_PMD) {
> > +               WARN_ON_ONCE(1);
> > +               return;
> > +       }
> > +
> > +       spin_lock_irq(&mapping->tree_lock);
> > +       /*
> > +        * Regular page slots are stabilized by the page lock even
> > +        * without the tree itself locked.  These unlocked entries
> > +        * need verification under the tree lock.
> > +        */
> > +       if (!__radix_tree_lookup(page_tree, index, &node, &slot))
> > +               goto unlock;
> > +       if (*slot != entry)
> > +               goto unlock;
> > +
> > +       /* another fsync thread may have already written back this entry */
> > +       if (!radix_tree_tag_get(page_tree, index, PAGECACHE_TAG_TOWRITE))
> > +               goto unlock;
> > +
> > +       radix_tree_tag_clear(page_tree, index, PAGECACHE_TAG_TOWRITE);
> > +
> > +       if (type == RADIX_DAX_PMD)
> > +               wb_cache_pmem(RADIX_DAX_ADDR(entry), PMD_SIZE);
> > +       else
> > +               wb_cache_pmem(RADIX_DAX_ADDR(entry), PAGE_SIZE);
> 
> Hi Ross, I should have realized this sooner, but what guarantees that
> the address returned by RADIX_DAX_ADDR(entry) is still valid at this
> point?  I think we need to store the sector in the radix tree and then
> perform a new dax_map_atomic() operation to either lookup a valid
> address or fail the sync request.  Otherwise, if the device is gone
> we'll crash, or write into some other random vmalloc address space.

Ah, good point, thank you.  v4 of this series is based on a version of
DAX where we aren't properly dealing with PMEM device removal.  I've got an
updated version that merges with your dax_map_atomic() changes, and I'll add
this change into v5 which I will send out today.  Thank you for the
suggestion.

One clarification, with the code as it is in v4 we are only doing
clflush/clflushopt/clwb instructions on the kaddr we've stored in the radix
tree, so I don't think that there is actually a risk of us doing a "write into
some other random vmalloc address space"?  I think at worse we will end up
clflushing an address that either isn't mapped or has been remapped by someone
else.  Or are you worried that the clflush would trigger a cache writeback to
a memory address where writes have side effects, thus triggering the side
effect?

I definitely think it needs to be fixed, I'm just trying to make sure I
understood your comment.

Re: [PATCH v5 4/7] dax: add support for fsync/sync

[Ross Zwisler]

On Sat, Dec 19, 2015 at 10:37:46AM -0800, Dan Williams wrote:
> On Fri, Dec 18, 2015 at 9:22 PM, Ross Zwisler
> <ross.zwisler@linux.intel.com> wrote:
> > To properly handle fsync/msync in an efficient way DAX needs to track dirty
> > pages so it is able to flush them durably to media on demand.
> >
> > The tracking of dirty pages is done via the radix tree in struct
> > address_space.  This radix tree is already used by the page writeback
> > infrastructure for tracking dirty pages associated with an open file, and
> > it already has support for exceptional (non struct page*) entries.  We
> > build upon these features to add exceptional entries to the radix tree for
> > DAX dirty PMD or PTE pages at fault time.
> >
> > Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
> [..]
> > +static void dax_writeback_one(struct address_space *mapping, pgoff_t index,
> > +               void *entry)
> > +{
> > +       struct radix_tree_root *page_tree = &mapping->page_tree;
> > +       int type = RADIX_DAX_TYPE(entry);
> > +       struct radix_tree_node *node;
> > +       void **slot;
> > +
> > +       if (type != RADIX_DAX_PTE && type != RADIX_DAX_PMD) {
> > +               WARN_ON_ONCE(1);
> > +               return;
> > +       }
> > +
> > +       spin_lock_irq(&mapping->tree_lock);
> > +       /*
> > +        * Regular page slots are stabilized by the page lock even
> > +        * without the tree itself locked.  These unlocked entries
> > +        * need verification under the tree lock.
> > +        */
> > +       if (!__radix_tree_lookup(page_tree, index, &node, &slot))
> > +               goto unlock;
> > +       if (*slot != entry)
> > +               goto unlock;
> > +
> > +       /* another fsync thread may have already written back this entry */
> > +       if (!radix_tree_tag_get(page_tree, index, PAGECACHE_TAG_TOWRITE))
> > +               goto unlock;
> > +
> > +       radix_tree_tag_clear(page_tree, index, PAGECACHE_TAG_TOWRITE);
> > +
> > +       if (type == RADIX_DAX_PMD)
> > +               wb_cache_pmem(RADIX_DAX_ADDR(entry), PMD_SIZE);
> > +       else
> > +               wb_cache_pmem(RADIX_DAX_ADDR(entry), PAGE_SIZE);
> 
> Hi Ross, I should have realized this sooner, but what guarantees that
> the address returned by RADIX_DAX_ADDR(entry) is still valid at this
> point?  I think we need to store the sector in the radix tree and then
> perform a new dax_map_atomic() operation to either lookup a valid
> address or fail the sync request.  Otherwise, if the device is gone
> we'll crash, or write into some other random vmalloc address space.

Ah, good point, thank you.  v4 of this series is based on a version of
DAX where we aren't properly dealing with PMEM device removal.  I've got an
updated version that merges with your dax_map_atomic() changes, and I'll add
this change into v5 which I will send out today.  Thank you for the
suggestion.

One clarification, with the code as it is in v4 we are only doing
clflush/clflushopt/clwb instructions on the kaddr we've stored in the radix
tree, so I don't think that there is actually a risk of us doing a "write into
some other random vmalloc address space"?  I think at worse we will end up
clflushing an address that either isn't mapped or has been remapped by someone
else.  Or are you worried that the clflush would trigger a cache writeback to
a memory address where writes have side effects, thus triggering the side
effect?

I definitely think it needs to be fixed, I'm just trying to make sure I
understood your comment.

_______________________________________________
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http://oss.sgi.com/mailman/listinfo/xfs

Re: [PATCH v5 2/7] dax: support dirty DAX entries in radix tree

[Jan Kara]

On Fri 18-12-15 22:22:15, Ross Zwisler wrote:
> Add support for tracking dirty DAX entries in the struct address_space
> radix tree.  This tree is already used for dirty page writeback, and it
> already supports the use of exceptional (non struct page*) entries.
> 
> In order to properly track dirty DAX pages we will insert new exceptional
> entries into the radix tree that represent dirty DAX PTE or PMD pages.
> These exceptional entries will also contain the writeback addresses for the
> PTE or PMD faults that we can use at fsync/msync time.
> 
> There are currently two types of exceptional entries (shmem and shadow)
> that can be placed into the radix tree, and this adds a third.  We rely on
> the fact that only one type of exceptional entry can be found in a given
> radix tree based on its usage.  This happens for free with DAX vs shmem but
> we explicitly prevent shadow entries from being added to radix trees for
> DAX mappings.
> 
> The only shadow entries that would be generated for DAX radix trees would
> be to track zero page mappings that were created for holes.  These pages
> would receive minimal benefit from having shadow entries, and the choice
> to have only one type of exceptional entry in a given radix tree makes the
> logic simpler both in clear_exceptional_entry() and in the rest of DAX.
> 
> Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>

The patch looks good to me. Just one comment: When we have this exclusion
between different types of exceptional entries, there is no real need to
have separate counters of 'shadow' and 'dax' entries, is there? We can have
one 'nrexceptional' counter and don't have to grow struct inode
unnecessarily which would be really welcome since DAX isn't a mainstream
feature. Could you please change the code? Thanks!

								Honza
> ---
>  fs/block_dev.c             |  3 ++-
>  fs/inode.c                 |  1 +
>  include/linux/dax.h        |  5 ++++
>  include/linux/fs.h         |  1 +
>  include/linux/radix-tree.h |  9 +++++++
>  mm/filemap.c               | 13 +++++++---
>  mm/truncate.c              | 64 +++++++++++++++++++++++++++-------------------
>  mm/vmscan.c                |  9 ++++++-
>  8 files changed, 73 insertions(+), 32 deletions(-)
> 
> diff --git a/fs/block_dev.c b/fs/block_dev.c
> index c25639e..226dacc 100644
> --- a/fs/block_dev.c
> +++ b/fs/block_dev.c
> @@ -75,7 +75,8 @@ void kill_bdev(struct block_device *bdev)
>  {
>  	struct address_space *mapping = bdev->bd_inode->i_mapping;
>  
> -	if (mapping->nrpages == 0 && mapping->nrshadows == 0)
> +	if (mapping->nrpages == 0 && mapping->nrshadows == 0 &&
> +			mapping->nrdax == 0)
>  		return;
>  
>  	invalidate_bh_lrus();
> diff --git a/fs/inode.c b/fs/inode.c
> index 1be5f90..79d828f 100644
> --- a/fs/inode.c
> +++ b/fs/inode.c
> @@ -496,6 +496,7 @@ void clear_inode(struct inode *inode)
>  	spin_lock_irq(&inode->i_data.tree_lock);
>  	BUG_ON(inode->i_data.nrpages);
>  	BUG_ON(inode->i_data.nrshadows);
> +	BUG_ON(inode->i_data.nrdax);
>  	spin_unlock_irq(&inode->i_data.tree_lock);
>  	BUG_ON(!list_empty(&inode->i_data.private_list));
>  	BUG_ON(!(inode->i_state & I_FREEING));
> diff --git a/include/linux/dax.h b/include/linux/dax.h
> index b415e52..e9d57f68 100644
> --- a/include/linux/dax.h
> +++ b/include/linux/dax.h
> @@ -36,4 +36,9 @@ static inline bool vma_is_dax(struct vm_area_struct *vma)
>  {
>  	return vma->vm_file && IS_DAX(vma->vm_file->f_mapping->host);
>  }
> +
> +static inline bool dax_mapping(struct address_space *mapping)
> +{
> +	return mapping->host && IS_DAX(mapping->host);
> +}
>  #endif
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 3aa5142..b9ac534 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -433,6 +433,7 @@ struct address_space {
>  	/* Protected by tree_lock together with the radix tree */
>  	unsigned long		nrpages;	/* number of total pages */
>  	unsigned long		nrshadows;	/* number of shadow entries */
> +	unsigned long		nrdax;	        /* number of DAX entries */
>  	pgoff_t			writeback_index;/* writeback starts here */
>  	const struct address_space_operations *a_ops;	/* methods */
>  	unsigned long		flags;		/* error bits/gfp mask */
> diff --git a/include/linux/radix-tree.h b/include/linux/radix-tree.h
> index 33170db..f793c99 100644
> --- a/include/linux/radix-tree.h
> +++ b/include/linux/radix-tree.h
> @@ -51,6 +51,15 @@
>  #define RADIX_TREE_EXCEPTIONAL_ENTRY	2
>  #define RADIX_TREE_EXCEPTIONAL_SHIFT	2
>  
> +#define RADIX_DAX_MASK	0xf
> +#define RADIX_DAX_PTE  (0x4 | RADIX_TREE_EXCEPTIONAL_ENTRY)
> +#define RADIX_DAX_PMD  (0x8 | RADIX_TREE_EXCEPTIONAL_ENTRY)
> +#define RADIX_DAX_TYPE(entry) ((__force unsigned long)entry & RADIX_DAX_MASK)
> +#define RADIX_DAX_ADDR(entry) ((void __pmem *)((unsigned long)entry & \
> +			~RADIX_DAX_MASK))
> +#define RADIX_DAX_ENTRY(addr, pmd) ((void *)((__force unsigned long)addr | \
> +			(pmd ? RADIX_DAX_PMD : RADIX_DAX_PTE)))
> +
>  static inline int radix_tree_is_indirect_ptr(void *ptr)
>  {
>  	return (int)((unsigned long)ptr & RADIX_TREE_INDIRECT_PTR);
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 1bb0076..167a4d9 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -11,6 +11,7 @@
>   */
>  #include <linux/export.h>
>  #include <linux/compiler.h>
> +#include <linux/dax.h>
>  #include <linux/fs.h>
>  #include <linux/uaccess.h>
>  #include <linux/capability.h>
> @@ -579,6 +580,12 @@ static int page_cache_tree_insert(struct address_space *mapping,
>  		p = radix_tree_deref_slot_protected(slot, &mapping->tree_lock);
>  		if (!radix_tree_exceptional_entry(p))
>  			return -EEXIST;
> +
> +		if (dax_mapping(mapping)) {
> +			WARN_ON(1);
> +			return -EINVAL;
> +		}
> +
>  		if (shadowp)
>  			*shadowp = p;
>  		mapping->nrshadows--;
> @@ -1242,9 +1249,9 @@ repeat:
>  			if (radix_tree_deref_retry(page))
>  				goto restart;
>  			/*
> -			 * A shadow entry of a recently evicted page,
> -			 * or a swap entry from shmem/tmpfs.  Return
> -			 * it without attempting to raise page count.
> +			 * A shadow entry of a recently evicted page, a swap
> +			 * entry from shmem/tmpfs or a DAX entry.  Return it
> +			 * without attempting to raise page count.
>  			 */
>  			goto export;
>  		}
> diff --git a/mm/truncate.c b/mm/truncate.c
> index 76e35ad..1dc9f29 100644
> --- a/mm/truncate.c
> +++ b/mm/truncate.c
> @@ -9,6 +9,7 @@
>  
>  #include <linux/kernel.h>
>  #include <linux/backing-dev.h>
> +#include <linux/dax.h>
>  #include <linux/gfp.h>
>  #include <linux/mm.h>
>  #include <linux/swap.h>
> @@ -34,31 +35,39 @@ static void clear_exceptional_entry(struct address_space *mapping,
>  		return;
>  
>  	spin_lock_irq(&mapping->tree_lock);
> -	/*
> -	 * Regular page slots are stabilized by the page lock even
> -	 * without the tree itself locked.  These unlocked entries
> -	 * need verification under the tree lock.
> -	 */
> -	if (!__radix_tree_lookup(&mapping->page_tree, index, &node, &slot))
> -		goto unlock;
> -	if (*slot != entry)
> -		goto unlock;
> -	radix_tree_replace_slot(slot, NULL);
> -	mapping->nrshadows--;
> -	if (!node)
> -		goto unlock;
> -	workingset_node_shadows_dec(node);
> -	/*
> -	 * Don't track node without shadow entries.
> -	 *
> -	 * Avoid acquiring the list_lru lock if already untracked.
> -	 * The list_empty() test is safe as node->private_list is
> -	 * protected by mapping->tree_lock.
> -	 */
> -	if (!workingset_node_shadows(node) &&
> -	    !list_empty(&node->private_list))
> -		list_lru_del(&workingset_shadow_nodes, &node->private_list);
> -	__radix_tree_delete_node(&mapping->page_tree, node);
> +
> +	if (dax_mapping(mapping)) {
> +		if (radix_tree_delete_item(&mapping->page_tree, index, entry))
> +			mapping->nrdax--;
> +	} else {
> +		/*
> +		 * Regular page slots are stabilized by the page lock even
> +		 * without the tree itself locked.  These unlocked entries
> +		 * need verification under the tree lock.
> +		 */
> +		if (!__radix_tree_lookup(&mapping->page_tree, index, &node,
> +					&slot))
> +			goto unlock;
> +		if (*slot != entry)
> +			goto unlock;
> +		radix_tree_replace_slot(slot, NULL);
> +		mapping->nrshadows--;
> +		if (!node)
> +			goto unlock;
> +		workingset_node_shadows_dec(node);
> +		/*
> +		 * Don't track node without shadow entries.
> +		 *
> +		 * Avoid acquiring the list_lru lock if already untracked.
> +		 * The list_empty() test is safe as node->private_list is
> +		 * protected by mapping->tree_lock.
> +		 */
> +		if (!workingset_node_shadows(node) &&
> +		    !list_empty(&node->private_list))
> +			list_lru_del(&workingset_shadow_nodes,
> +					&node->private_list);
> +		__radix_tree_delete_node(&mapping->page_tree, node);
> +	}
>  unlock:
>  	spin_unlock_irq(&mapping->tree_lock);
>  }
> @@ -228,7 +237,8 @@ void truncate_inode_pages_range(struct address_space *mapping,
>  	int		i;
>  
>  	cleancache_invalidate_inode(mapping);
> -	if (mapping->nrpages == 0 && mapping->nrshadows == 0)
> +	if (mapping->nrpages == 0 && mapping->nrshadows == 0 &&
> +			mapping->nrdax == 0)
>  		return;
>  
>  	/* Offsets within partial pages */
> @@ -423,7 +433,7 @@ void truncate_inode_pages_final(struct address_space *mapping)
>  	smp_rmb();
>  	nrshadows = mapping->nrshadows;
>  
> -	if (nrpages || nrshadows) {
> +	if (nrpages || nrshadows || mapping->nrdax) {
>  		/*
>  		 * As truncation uses a lockless tree lookup, cycle
>  		 * the tree lock to make sure any ongoing tree
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 2aec424..8071956 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -46,6 +46,7 @@
>  #include <linux/oom.h>
>  #include <linux/prefetch.h>
>  #include <linux/printk.h>
> +#include <linux/dax.h>
>  
>  #include <asm/tlbflush.h>
>  #include <asm/div64.h>
> @@ -671,9 +672,15 @@ static int __remove_mapping(struct address_space *mapping, struct page *page,
>  		 * inode reclaim needs to empty out the radix tree or
>  		 * the nodes are lost.  Don't plant shadows behind its
>  		 * back.
> +		 *
> +		 * We also don't store shadows for DAX mappings because the
> +		 * only page cache pages found in these are zero pages
> +		 * covering holes, and because we don't want to mix DAX
> +		 * exceptional entries and shadow exceptional entries in the
> +		 * same page_tree.
>  		 */
>  		if (reclaimed && page_is_file_cache(page) &&
> -		    !mapping_exiting(mapping))
> +		    !mapping_exiting(mapping) && !dax_mapping(mapping))
>  			shadow = workingset_eviction(mapping, page);
>  		__delete_from_page_cache(page, shadow, memcg);
>  		spin_unlock_irqrestore(&mapping->tree_lock, flags);
> -- 
> 2.5.0
> 
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

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Re: [PATCH v5 2/7] dax: support dirty DAX entries in radix tree

[Jan Kara]

On Fri 18-12-15 22:22:15, Ross Zwisler wrote:
> Add support for tracking dirty DAX entries in the struct address_space
> radix tree.  This tree is already used for dirty page writeback, and it
> already supports the use of exceptional (non struct page*) entries.
> 
> In order to properly track dirty DAX pages we will insert new exceptional
> entries into the radix tree that represent dirty DAX PTE or PMD pages.
> These exceptional entries will also contain the writeback addresses for the
> PTE or PMD faults that we can use at fsync/msync time.
> 
> There are currently two types of exceptional entries (shmem and shadow)
> that can be placed into the radix tree, and this adds a third.  We rely on
> the fact that only one type of exceptional entry can be found in a given
> radix tree based on its usage.  This happens for free with DAX vs shmem but
> we explicitly prevent shadow entries from being added to radix trees for
> DAX mappings.
> 
> The only shadow entries that would be generated for DAX radix trees would
> be to track zero page mappings that were created for holes.  These pages
> would receive minimal benefit from having shadow entries, and the choice
> to have only one type of exceptional entry in a given radix tree makes the
> logic simpler both in clear_exceptional_entry() and in the rest of DAX.
> 
> Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>

The patch looks good to me. Just one comment: When we have this exclusion
between different types of exceptional entries, there is no real need to
have separate counters of 'shadow' and 'dax' entries, is there? We can have
one 'nrexceptional' counter and don't have to grow struct inode
unnecessarily which would be really welcome since DAX isn't a mainstream
feature. Could you please change the code? Thanks!

								Honza
> ---
>  fs/block_dev.c             |  3 ++-
>  fs/inode.c                 |  1 +
>  include/linux/dax.h        |  5 ++++
>  include/linux/fs.h         |  1 +
>  include/linux/radix-tree.h |  9 +++++++
>  mm/filemap.c               | 13 +++++++---
>  mm/truncate.c              | 64 +++++++++++++++++++++++++++-------------------
>  mm/vmscan.c                |  9 ++++++-
>  8 files changed, 73 insertions(+), 32 deletions(-)
> 
> diff --git a/fs/block_dev.c b/fs/block_dev.c
> index c25639e..226dacc 100644
> --- a/fs/block_dev.c
> +++ b/fs/block_dev.c
> @@ -75,7 +75,8 @@ void kill_bdev(struct block_device *bdev)
>  {
>  	struct address_space *mapping = bdev->bd_inode->i_mapping;
>  
> -	if (mapping->nrpages == 0 && mapping->nrshadows == 0)
> +	if (mapping->nrpages == 0 && mapping->nrshadows == 0 &&
> +			mapping->nrdax == 0)
>  		return;
>  
>  	invalidate_bh_lrus();
> diff --git a/fs/inode.c b/fs/inode.c
> index 1be5f90..79d828f 100644
> --- a/fs/inode.c
> +++ b/fs/inode.c
> @@ -496,6 +496,7 @@ void clear_inode(struct inode *inode)
>  	spin_lock_irq(&inode->i_data.tree_lock);
>  	BUG_ON(inode->i_data.nrpages);
>  	BUG_ON(inode->i_data.nrshadows);
> +	BUG_ON(inode->i_data.nrdax);
>  	spin_unlock_irq(&inode->i_data.tree_lock);
>  	BUG_ON(!list_empty(&inode->i_data.private_list));
>  	BUG_ON(!(inode->i_state & I_FREEING));
> diff --git a/include/linux/dax.h b/include/linux/dax.h
> index b415e52..e9d57f68 100644
> --- a/include/linux/dax.h
> +++ b/include/linux/dax.h
> @@ -36,4 +36,9 @@ static inline bool vma_is_dax(struct vm_area_struct *vma)
>  {
>  	return vma->vm_file && IS_DAX(vma->vm_file->f_mapping->host);
>  }
> +
> +static inline bool dax_mapping(struct address_space *mapping)
> +{
> +	return mapping->host && IS_DAX(mapping->host);
> +}
>  #endif
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 3aa5142..b9ac534 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -433,6 +433,7 @@ struct address_space {
>  	/* Protected by tree_lock together with the radix tree */
>  	unsigned long		nrpages;	/* number of total pages */
>  	unsigned long		nrshadows;	/* number of shadow entries */
> +	unsigned long		nrdax;	        /* number of DAX entries */
>  	pgoff_t			writeback_index;/* writeback starts here */
>  	const struct address_space_operations *a_ops;	/* methods */
>  	unsigned long		flags;		/* error bits/gfp mask */
> diff --git a/include/linux/radix-tree.h b/include/linux/radix-tree.h
> index 33170db..f793c99 100644
> --- a/include/linux/radix-tree.h
> +++ b/include/linux/radix-tree.h
> @@ -51,6 +51,15 @@
>  #define RADIX_TREE_EXCEPTIONAL_ENTRY	2
>  #define RADIX_TREE_EXCEPTIONAL_SHIFT	2
>  
> +#define RADIX_DAX_MASK	0xf
> +#define RADIX_DAX_PTE  (0x4 | RADIX_TREE_EXCEPTIONAL_ENTRY)
> +#define RADIX_DAX_PMD  (0x8 | RADIX_TREE_EXCEPTIONAL_ENTRY)
> +#define RADIX_DAX_TYPE(entry) ((__force unsigned long)entry & RADIX_DAX_MASK)
> +#define RADIX_DAX_ADDR(entry) ((void __pmem *)((unsigned long)entry & \
> +			~RADIX_DAX_MASK))
> +#define RADIX_DAX_ENTRY(addr, pmd) ((void *)((__force unsigned long)addr | \
> +			(pmd ? RADIX_DAX_PMD : RADIX_DAX_PTE)))
> +
>  static inline int radix_tree_is_indirect_ptr(void *ptr)
>  {
>  	return (int)((unsigned long)ptr & RADIX_TREE_INDIRECT_PTR);
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 1bb0076..167a4d9 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -11,6 +11,7 @@
>   */
>  #include <linux/export.h>
>  #include <linux/compiler.h>
> +#include <linux/dax.h>
>  #include <linux/fs.h>
>  #include <linux/uaccess.h>
>  #include <linux/capability.h>
> @@ -579,6 +580,12 @@ static int page_cache_tree_insert(struct address_space *mapping,
>  		p = radix_tree_deref_slot_protected(slot, &mapping->tree_lock);
>  		if (!radix_tree_exceptional_entry(p))
>  			return -EEXIST;
> +
> +		if (dax_mapping(mapping)) {
> +			WARN_ON(1);
> +			return -EINVAL;
> +		}
> +
>  		if (shadowp)
>  			*shadowp = p;
>  		mapping->nrshadows--;
> @@ -1242,9 +1249,9 @@ repeat:
>  			if (radix_tree_deref_retry(page))
>  				goto restart;
>  			/*
> -			 * A shadow entry of a recently evicted page,
> -			 * or a swap entry from shmem/tmpfs.  Return
> -			 * it without attempting to raise page count.
> +			 * A shadow entry of a recently evicted page, a swap
> +			 * entry from shmem/tmpfs or a DAX entry.  Return it
> +			 * without attempting to raise page count.
>  			 */
>  			goto export;
>  		}
> diff --git a/mm/truncate.c b/mm/truncate.c
> index 76e35ad..1dc9f29 100644
> --- a/mm/truncate.c
> +++ b/mm/truncate.c
> @@ -9,6 +9,7 @@
>  
>  #include <linux/kernel.h>
>  #include <linux/backing-dev.h>
> +#include <linux/dax.h>
>  #include <linux/gfp.h>
>  #include <linux/mm.h>
>  #include <linux/swap.h>
> @@ -34,31 +35,39 @@ static void clear_exceptional_entry(struct address_space *mapping,
>  		return;
>  
>  	spin_lock_irq(&mapping->tree_lock);
> -	/*
> -	 * Regular page slots are stabilized by the page lock even
> -	 * without the tree itself locked.  These unlocked entries
> -	 * need verification under the tree lock.
> -	 */
> -	if (!__radix_tree_lookup(&mapping->page_tree, index, &node, &slot))
> -		goto unlock;
> -	if (*slot != entry)
> -		goto unlock;
> -	radix_tree_replace_slot(slot, NULL);
> -	mapping->nrshadows--;
> -	if (!node)
> -		goto unlock;
> -	workingset_node_shadows_dec(node);
> -	/*
> -	 * Don't track node without shadow entries.
> -	 *
> -	 * Avoid acquiring the list_lru lock if already untracked.
> -	 * The list_empty() test is safe as node->private_list is
> -	 * protected by mapping->tree_lock.
> -	 */
> -	if (!workingset_node_shadows(node) &&
> -	    !list_empty(&node->private_list))
> -		list_lru_del(&workingset_shadow_nodes, &node->private_list);
> -	__radix_tree_delete_node(&mapping->page_tree, node);
> +
> +	if (dax_mapping(mapping)) {
> +		if (radix_tree_delete_item(&mapping->page_tree, index, entry))
> +			mapping->nrdax--;
> +	} else {
> +		/*
> +		 * Regular page slots are stabilized by the page lock even
> +		 * without the tree itself locked.  These unlocked entries
> +		 * need verification under the tree lock.
> +		 */
> +		if (!__radix_tree_lookup(&mapping->page_tree, index, &node,
> +					&slot))
> +			goto unlock;
> +		if (*slot != entry)
> +			goto unlock;
> +		radix_tree_replace_slot(slot, NULL);
> +		mapping->nrshadows--;
> +		if (!node)
> +			goto unlock;
> +		workingset_node_shadows_dec(node);
> +		/*
> +		 * Don't track node without shadow entries.
> +		 *
> +		 * Avoid acquiring the list_lru lock if already untracked.
> +		 * The list_empty() test is safe as node->private_list is
> +		 * protected by mapping->tree_lock.
> +		 */
> +		if (!workingset_node_shadows(node) &&
> +		    !list_empty(&node->private_list))
> +			list_lru_del(&workingset_shadow_nodes,
> +					&node->private_list);
> +		__radix_tree_delete_node(&mapping->page_tree, node);
> +	}
>  unlock:
>  	spin_unlock_irq(&mapping->tree_lock);
>  }
> @@ -228,7 +237,8 @@ void truncate_inode_pages_range(struct address_space *mapping,
>  	int		i;
>  
>  	cleancache_invalidate_inode(mapping);
> -	if (mapping->nrpages == 0 && mapping->nrshadows == 0)
> +	if (mapping->nrpages == 0 && mapping->nrshadows == 0 &&
> +			mapping->nrdax == 0)
>  		return;
>  
>  	/* Offsets within partial pages */
> @@ -423,7 +433,7 @@ void truncate_inode_pages_final(struct address_space *mapping)
>  	smp_rmb();
>  	nrshadows = mapping->nrshadows;
>  
> -	if (nrpages || nrshadows) {
> +	if (nrpages || nrshadows || mapping->nrdax) {
>  		/*
>  		 * As truncation uses a lockless tree lookup, cycle
>  		 * the tree lock to make sure any ongoing tree
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 2aec424..8071956 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -46,6 +46,7 @@
>  #include <linux/oom.h>
>  #include <linux/prefetch.h>
>  #include <linux/printk.h>
> +#include <linux/dax.h>
>  
>  #include <asm/tlbflush.h>
>  #include <asm/div64.h>
> @@ -671,9 +672,15 @@ static int __remove_mapping(struct address_space *mapping, struct page *page,
>  		 * inode reclaim needs to empty out the radix tree or
>  		 * the nodes are lost.  Don't plant shadows behind its
>  		 * back.
> +		 *
> +		 * We also don't store shadows for DAX mappings because the
> +		 * only page cache pages found in these are zero pages
> +		 * covering holes, and because we don't want to mix DAX
> +		 * exceptional entries and shadow exceptional entries in the
> +		 * same page_tree.
>  		 */
>  		if (reclaimed && page_is_file_cache(page) &&
> -		    !mapping_exiting(mapping))
> +		    !mapping_exiting(mapping) && !dax_mapping(mapping))
>  			shadow = workingset_eviction(mapping, page);
>  		__delete_from_page_cache(page, shadow, memcg);
>  		spin_unlock_irqrestore(&mapping->tree_lock, flags);
> -- 
> 2.5.0
> 
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

Re: [PATCH v5 2/7] dax: support dirty DAX entries in radix tree

[Jan Kara]

On Fri 18-12-15 22:22:15, Ross Zwisler wrote:
> Add support for tracking dirty DAX entries in the struct address_space
> radix tree.  This tree is already used for dirty page writeback, and it
> already supports the use of exceptional (non struct page*) entries.
> 
> In order to properly track dirty DAX pages we will insert new exceptional
> entries into the radix tree that represent dirty DAX PTE or PMD pages.
> These exceptional entries will also contain the writeback addresses for the
> PTE or PMD faults that we can use at fsync/msync time.
> 
> There are currently two types of exceptional entries (shmem and shadow)
> that can be placed into the radix tree, and this adds a third.  We rely on
> the fact that only one type of exceptional entry can be found in a given
> radix tree based on its usage.  This happens for free with DAX vs shmem but
> we explicitly prevent shadow entries from being added to radix trees for
> DAX mappings.
> 
> The only shadow entries that would be generated for DAX radix trees would
> be to track zero page mappings that were created for holes.  These pages
> would receive minimal benefit from having shadow entries, and the choice
> to have only one type of exceptional entry in a given radix tree makes the
> logic simpler both in clear_exceptional_entry() and in the rest of DAX.
> 
> Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>

The patch looks good to me. Just one comment: When we have this exclusion
between different types of exceptional entries, there is no real need to
have separate counters of 'shadow' and 'dax' entries, is there? We can have
one 'nrexceptional' counter and don't have to grow struct inode
unnecessarily which would be really welcome since DAX isn't a mainstream
feature. Could you please change the code? Thanks!

								Honza
> ---
>  fs/block_dev.c             |  3 ++-
>  fs/inode.c                 |  1 +
>  include/linux/dax.h        |  5 ++++
>  include/linux/fs.h         |  1 +
>  include/linux/radix-tree.h |  9 +++++++
>  mm/filemap.c               | 13 +++++++---
>  mm/truncate.c              | 64 +++++++++++++++++++++++++++-------------------
>  mm/vmscan.c                |  9 ++++++-
>  8 files changed, 73 insertions(+), 32 deletions(-)
> 
> diff --git a/fs/block_dev.c b/fs/block_dev.c
> index c25639e..226dacc 100644
> --- a/fs/block_dev.c
> +++ b/fs/block_dev.c
> @@ -75,7 +75,8 @@ void kill_bdev(struct block_device *bdev)
>  {
>  	struct address_space *mapping = bdev->bd_inode->i_mapping;
>  
> -	if (mapping->nrpages == 0 && mapping->nrshadows == 0)
> +	if (mapping->nrpages == 0 && mapping->nrshadows == 0 &&
> +			mapping->nrdax == 0)
>  		return;
>  
>  	invalidate_bh_lrus();
> diff --git a/fs/inode.c b/fs/inode.c
> index 1be5f90..79d828f 100644
> --- a/fs/inode.c
> +++ b/fs/inode.c
> @@ -496,6 +496,7 @@ void clear_inode(struct inode *inode)
>  	spin_lock_irq(&inode->i_data.tree_lock);
>  	BUG_ON(inode->i_data.nrpages);
>  	BUG_ON(inode->i_data.nrshadows);
> +	BUG_ON(inode->i_data.nrdax);
>  	spin_unlock_irq(&inode->i_data.tree_lock);
>  	BUG_ON(!list_empty(&inode->i_data.private_list));
>  	BUG_ON(!(inode->i_state & I_FREEING));
> diff --git a/include/linux/dax.h b/include/linux/dax.h
> index b415e52..e9d57f68 100644
> --- a/include/linux/dax.h
> +++ b/include/linux/dax.h
> @@ -36,4 +36,9 @@ static inline bool vma_is_dax(struct vm_area_struct *vma)
>  {
>  	return vma->vm_file && IS_DAX(vma->vm_file->f_mapping->host);
>  }
> +
> +static inline bool dax_mapping(struct address_space *mapping)
> +{
> +	return mapping->host && IS_DAX(mapping->host);
> +}
>  #endif
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 3aa5142..b9ac534 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -433,6 +433,7 @@ struct address_space {
>  	/* Protected by tree_lock together with the radix tree */
>  	unsigned long		nrpages;	/* number of total pages */
>  	unsigned long		nrshadows;	/* number of shadow entries */
> +	unsigned long		nrdax;	        /* number of DAX entries */
>  	pgoff_t			writeback_index;/* writeback starts here */
>  	const struct address_space_operations *a_ops;	/* methods */
>  	unsigned long		flags;		/* error bits/gfp mask */
> diff --git a/include/linux/radix-tree.h b/include/linux/radix-tree.h
> index 33170db..f793c99 100644
> --- a/include/linux/radix-tree.h
> +++ b/include/linux/radix-tree.h
> @@ -51,6 +51,15 @@
>  #define RADIX_TREE_EXCEPTIONAL_ENTRY	2
>  #define RADIX_TREE_EXCEPTIONAL_SHIFT	2
>  
> +#define RADIX_DAX_MASK	0xf
> +#define RADIX_DAX_PTE  (0x4 | RADIX_TREE_EXCEPTIONAL_ENTRY)
> +#define RADIX_DAX_PMD  (0x8 | RADIX_TREE_EXCEPTIONAL_ENTRY)
> +#define RADIX_DAX_TYPE(entry) ((__force unsigned long)entry & RADIX_DAX_MASK)
> +#define RADIX_DAX_ADDR(entry) ((void __pmem *)((unsigned long)entry & \
> +			~RADIX_DAX_MASK))
> +#define RADIX_DAX_ENTRY(addr, pmd) ((void *)((__force unsigned long)addr | \
> +			(pmd ? RADIX_DAX_PMD : RADIX_DAX_PTE)))
> +
>  static inline int radix_tree_is_indirect_ptr(void *ptr)
>  {
>  	return (int)((unsigned long)ptr & RADIX_TREE_INDIRECT_PTR);
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 1bb0076..167a4d9 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -11,6 +11,7 @@
>   */
>  #include <linux/export.h>
>  #include <linux/compiler.h>
> +#include <linux/dax.h>
>  #include <linux/fs.h>
>  #include <linux/uaccess.h>
>  #include <linux/capability.h>
> @@ -579,6 +580,12 @@ static int page_cache_tree_insert(struct address_space *mapping,
>  		p = radix_tree_deref_slot_protected(slot, &mapping->tree_lock);
>  		if (!radix_tree_exceptional_entry(p))
>  			return -EEXIST;
> +
> +		if (dax_mapping(mapping)) {
> +			WARN_ON(1);
> +			return -EINVAL;
> +		}
> +
>  		if (shadowp)
>  			*shadowp = p;
>  		mapping->nrshadows--;
> @@ -1242,9 +1249,9 @@ repeat:
>  			if (radix_tree_deref_retry(page))
>  				goto restart;
>  			/*
> -			 * A shadow entry of a recently evicted page,
> -			 * or a swap entry from shmem/tmpfs.  Return
> -			 * it without attempting to raise page count.
> +			 * A shadow entry of a recently evicted page, a swap
> +			 * entry from shmem/tmpfs or a DAX entry.  Return it
> +			 * without attempting to raise page count.
>  			 */
>  			goto export;
>  		}
> diff --git a/mm/truncate.c b/mm/truncate.c
> index 76e35ad..1dc9f29 100644
> --- a/mm/truncate.c
> +++ b/mm/truncate.c
> @@ -9,6 +9,7 @@
>  
>  #include <linux/kernel.h>
>  #include <linux/backing-dev.h>
> +#include <linux/dax.h>
>  #include <linux/gfp.h>
>  #include <linux/mm.h>
>  #include <linux/swap.h>
> @@ -34,31 +35,39 @@ static void clear_exceptional_entry(struct address_space *mapping,
>  		return;
>  
>  	spin_lock_irq(&mapping->tree_lock);
> -	/*
> -	 * Regular page slots are stabilized by the page lock even
> -	 * without the tree itself locked.  These unlocked entries
> -	 * need verification under the tree lock.
> -	 */
> -	if (!__radix_tree_lookup(&mapping->page_tree, index, &node, &slot))
> -		goto unlock;
> -	if (*slot != entry)
> -		goto unlock;
> -	radix_tree_replace_slot(slot, NULL);
> -	mapping->nrshadows--;
> -	if (!node)
> -		goto unlock;
> -	workingset_node_shadows_dec(node);
> -	/*
> -	 * Don't track node without shadow entries.
> -	 *
> -	 * Avoid acquiring the list_lru lock if already untracked.
> -	 * The list_empty() test is safe as node->private_list is
> -	 * protected by mapping->tree_lock.
> -	 */
> -	if (!workingset_node_shadows(node) &&
> -	    !list_empty(&node->private_list))
> -		list_lru_del(&workingset_shadow_nodes, &node->private_list);
> -	__radix_tree_delete_node(&mapping->page_tree, node);
> +
> +	if (dax_mapping(mapping)) {
> +		if (radix_tree_delete_item(&mapping->page_tree, index, entry))
> +			mapping->nrdax--;
> +	} else {
> +		/*
> +		 * Regular page slots are stabilized by the page lock even
> +		 * without the tree itself locked.  These unlocked entries
> +		 * need verification under the tree lock.
> +		 */
> +		if (!__radix_tree_lookup(&mapping->page_tree, index, &node,
> +					&slot))
> +			goto unlock;
> +		if (*slot != entry)
> +			goto unlock;
> +		radix_tree_replace_slot(slot, NULL);
> +		mapping->nrshadows--;
> +		if (!node)
> +			goto unlock;
> +		workingset_node_shadows_dec(node);
> +		/*
> +		 * Don't track node without shadow entries.
> +		 *
> +		 * Avoid acquiring the list_lru lock if already untracked.
> +		 * The list_empty() test is safe as node->private_list is
> +		 * protected by mapping->tree_lock.
> +		 */
> +		if (!workingset_node_shadows(node) &&
> +		    !list_empty(&node->private_list))
> +			list_lru_del(&workingset_shadow_nodes,
> +					&node->private_list);
> +		__radix_tree_delete_node(&mapping->page_tree, node);
> +	}
>  unlock:
>  	spin_unlock_irq(&mapping->tree_lock);
>  }
> @@ -228,7 +237,8 @@ void truncate_inode_pages_range(struct address_space *mapping,
>  	int		i;
>  
>  	cleancache_invalidate_inode(mapping);
> -	if (mapping->nrpages == 0 && mapping->nrshadows == 0)
> +	if (mapping->nrpages == 0 && mapping->nrshadows == 0 &&
> +			mapping->nrdax == 0)
>  		return;
>  
>  	/* Offsets within partial pages */
> @@ -423,7 +433,7 @@ void truncate_inode_pages_final(struct address_space *mapping)
>  	smp_rmb();
>  	nrshadows = mapping->nrshadows;
>  
> -	if (nrpages || nrshadows) {
> +	if (nrpages || nrshadows || mapping->nrdax) {
>  		/*
>  		 * As truncation uses a lockless tree lookup, cycle
>  		 * the tree lock to make sure any ongoing tree
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 2aec424..8071956 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -46,6 +46,7 @@
>  #include <linux/oom.h>
>  #include <linux/prefetch.h>
>  #include <linux/printk.h>
> +#include <linux/dax.h>
>  
>  #include <asm/tlbflush.h>
>  #include <asm/div64.h>
> @@ -671,9 +672,15 @@ static int __remove_mapping(struct address_space *mapping, struct page *page,
>  		 * inode reclaim needs to empty out the radix tree or
>  		 * the nodes are lost.  Don't plant shadows behind its
>  		 * back.
> +		 *
> +		 * We also don't store shadows for DAX mappings because the
> +		 * only page cache pages found in these are zero pages
> +		 * covering holes, and because we don't want to mix DAX
> +		 * exceptional entries and shadow exceptional entries in the
> +		 * same page_tree.
>  		 */
>  		if (reclaimed && page_is_file_cache(page) &&
> -		    !mapping_exiting(mapping))
> +		    !mapping_exiting(mapping) && !dax_mapping(mapping))
>  			shadow = workingset_eviction(mapping, page);
>  		__delete_from_page_cache(page, shadow, memcg);
>  		spin_unlock_irqrestore(&mapping->tree_lock, flags);
> -- 
> 2.5.0
> 
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

Re: [PATCH v5 2/7] dax: support dirty DAX entries in radix tree

[Jan Kara]

On Fri 18-12-15 22:22:15, Ross Zwisler wrote:
> Add support for tracking dirty DAX entries in the struct address_space
> radix tree.  This tree is already used for dirty page writeback, and it
> already supports the use of exceptional (non struct page*) entries.
> 
> In order to properly track dirty DAX pages we will insert new exceptional
> entries into the radix tree that represent dirty DAX PTE or PMD pages.
> These exceptional entries will also contain the writeback addresses for the
> PTE or PMD faults that we can use at fsync/msync time.
> 
> There are currently two types of exceptional entries (shmem and shadow)
> that can be placed into the radix tree, and this adds a third.  We rely on
> the fact that only one type of exceptional entry can be found in a given
> radix tree based on its usage.  This happens for free with DAX vs shmem but
> we explicitly prevent shadow entries from being added to radix trees for
> DAX mappings.
> 
> The only shadow entries that would be generated for DAX radix trees would
> be to track zero page mappings that were created for holes.  These pages
> would receive minimal benefit from having shadow entries, and the choice
> to have only one type of exceptional entry in a given radix tree makes the
> logic simpler both in clear_exceptional_entry() and in the rest of DAX.
> 
> Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>

The patch looks good to me. Just one comment: When we have this exclusion
between different types of exceptional entries, there is no real need to
have separate counters of 'shadow' and 'dax' entries, is there? We can have
one 'nrexceptional' counter and don't have to grow struct inode
unnecessarily which would be really welcome since DAX isn't a mainstream
feature. Could you please change the code? Thanks!

								Honza
> ---
>  fs/block_dev.c             |  3 ++-
>  fs/inode.c                 |  1 +
>  include/linux/dax.h        |  5 ++++
>  include/linux/fs.h         |  1 +
>  include/linux/radix-tree.h |  9 +++++++
>  mm/filemap.c               | 13 +++++++---
>  mm/truncate.c              | 64 +++++++++++++++++++++++++++-------------------
>  mm/vmscan.c                |  9 ++++++-
>  8 files changed, 73 insertions(+), 32 deletions(-)
> 
> diff --git a/fs/block_dev.c b/fs/block_dev.c
> index c25639e..226dacc 100644
> --- a/fs/block_dev.c
> +++ b/fs/block_dev.c
> @@ -75,7 +75,8 @@ void kill_bdev(struct block_device *bdev)
>  {
>  	struct address_space *mapping = bdev->bd_inode->i_mapping;
>  
> -	if (mapping->nrpages == 0 && mapping->nrshadows == 0)
> +	if (mapping->nrpages == 0 && mapping->nrshadows == 0 &&
> +			mapping->nrdax == 0)
>  		return;
>  
>  	invalidate_bh_lrus();
> diff --git a/fs/inode.c b/fs/inode.c
> index 1be5f90..79d828f 100644
> --- a/fs/inode.c
> +++ b/fs/inode.c
> @@ -496,6 +496,7 @@ void clear_inode(struct inode *inode)
>  	spin_lock_irq(&inode->i_data.tree_lock);
>  	BUG_ON(inode->i_data.nrpages);
>  	BUG_ON(inode->i_data.nrshadows);
> +	BUG_ON(inode->i_data.nrdax);
>  	spin_unlock_irq(&inode->i_data.tree_lock);
>  	BUG_ON(!list_empty(&inode->i_data.private_list));
>  	BUG_ON(!(inode->i_state & I_FREEING));
> diff --git a/include/linux/dax.h b/include/linux/dax.h
> index b415e52..e9d57f68 100644
> --- a/include/linux/dax.h
> +++ b/include/linux/dax.h
> @@ -36,4 +36,9 @@ static inline bool vma_is_dax(struct vm_area_struct *vma)
>  {
>  	return vma->vm_file && IS_DAX(vma->vm_file->f_mapping->host);
>  }
> +
> +static inline bool dax_mapping(struct address_space *mapping)
> +{
> +	return mapping->host && IS_DAX(mapping->host);
> +}
>  #endif
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 3aa5142..b9ac534 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -433,6 +433,7 @@ struct address_space {
>  	/* Protected by tree_lock together with the radix tree */
>  	unsigned long		nrpages;	/* number of total pages */
>  	unsigned long		nrshadows;	/* number of shadow entries */
> +	unsigned long		nrdax;	        /* number of DAX entries */
>  	pgoff_t			writeback_index;/* writeback starts here */
>  	const struct address_space_operations *a_ops;	/* methods */
>  	unsigned long		flags;		/* error bits/gfp mask */
> diff --git a/include/linux/radix-tree.h b/include/linux/radix-tree.h
> index 33170db..f793c99 100644
> --- a/include/linux/radix-tree.h
> +++ b/include/linux/radix-tree.h
> @@ -51,6 +51,15 @@
>  #define RADIX_TREE_EXCEPTIONAL_ENTRY	2
>  #define RADIX_TREE_EXCEPTIONAL_SHIFT	2
>  
> +#define RADIX_DAX_MASK	0xf
> +#define RADIX_DAX_PTE  (0x4 | RADIX_TREE_EXCEPTIONAL_ENTRY)
> +#define RADIX_DAX_PMD  (0x8 | RADIX_TREE_EXCEPTIONAL_ENTRY)
> +#define RADIX_DAX_TYPE(entry) ((__force unsigned long)entry & RADIX_DAX_MASK)
> +#define RADIX_DAX_ADDR(entry) ((void __pmem *)((unsigned long)entry & \
> +			~RADIX_DAX_MASK))
> +#define RADIX_DAX_ENTRY(addr, pmd) ((void *)((__force unsigned long)addr | \
> +			(pmd ? RADIX_DAX_PMD : RADIX_DAX_PTE)))
> +
>  static inline int radix_tree_is_indirect_ptr(void *ptr)
>  {
>  	return (int)((unsigned long)ptr & RADIX_TREE_INDIRECT_PTR);
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 1bb0076..167a4d9 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -11,6 +11,7 @@
>   */
>  #include <linux/export.h>
>  #include <linux/compiler.h>
> +#include <linux/dax.h>
>  #include <linux/fs.h>
>  #include <linux/uaccess.h>
>  #include <linux/capability.h>
> @@ -579,6 +580,12 @@ static int page_cache_tree_insert(struct address_space *mapping,
>  		p = radix_tree_deref_slot_protected(slot, &mapping->tree_lock);
>  		if (!radix_tree_exceptional_entry(p))
>  			return -EEXIST;
> +
> +		if (dax_mapping(mapping)) {
> +			WARN_ON(1);
> +			return -EINVAL;
> +		}
> +
>  		if (shadowp)
>  			*shadowp = p;
>  		mapping->nrshadows--;
> @@ -1242,9 +1249,9 @@ repeat:
>  			if (radix_tree_deref_retry(page))
>  				goto restart;
>  			/*
> -			 * A shadow entry of a recently evicted page,
> -			 * or a swap entry from shmem/tmpfs.  Return
> -			 * it without attempting to raise page count.
> +			 * A shadow entry of a recently evicted page, a swap
> +			 * entry from shmem/tmpfs or a DAX entry.  Return it
> +			 * without attempting to raise page count.
>  			 */
>  			goto export;
>  		}
> diff --git a/mm/truncate.c b/mm/truncate.c
> index 76e35ad..1dc9f29 100644
> --- a/mm/truncate.c
> +++ b/mm/truncate.c
> @@ -9,6 +9,7 @@
>  
>  #include <linux/kernel.h>
>  #include <linux/backing-dev.h>
> +#include <linux/dax.h>
>  #include <linux/gfp.h>
>  #include <linux/mm.h>
>  #include <linux/swap.h>
> @@ -34,31 +35,39 @@ static void clear_exceptional_entry(struct address_space *mapping,
>  		return;
>  
>  	spin_lock_irq(&mapping->tree_lock);
> -	/*
> -	 * Regular page slots are stabilized by the page lock even
> -	 * without the tree itself locked.  These unlocked entries
> -	 * need verification under the tree lock.
> -	 */
> -	if (!__radix_tree_lookup(&mapping->page_tree, index, &node, &slot))
> -		goto unlock;
> -	if (*slot != entry)
> -		goto unlock;
> -	radix_tree_replace_slot(slot, NULL);
> -	mapping->nrshadows--;
> -	if (!node)
> -		goto unlock;
> -	workingset_node_shadows_dec(node);
> -	/*
> -	 * Don't track node without shadow entries.
> -	 *
> -	 * Avoid acquiring the list_lru lock if already untracked.
> -	 * The list_empty() test is safe as node->private_list is
> -	 * protected by mapping->tree_lock.
> -	 */
> -	if (!workingset_node_shadows(node) &&
> -	    !list_empty(&node->private_list))
> -		list_lru_del(&workingset_shadow_nodes, &node->private_list);
> -	__radix_tree_delete_node(&mapping->page_tree, node);
> +
> +	if (dax_mapping(mapping)) {
> +		if (radix_tree_delete_item(&mapping->page_tree, index, entry))
> +			mapping->nrdax--;
> +	} else {
> +		/*
> +		 * Regular page slots are stabilized by the page lock even
> +		 * without the tree itself locked.  These unlocked entries
> +		 * need verification under the tree lock.
> +		 */
> +		if (!__radix_tree_lookup(&mapping->page_tree, index, &node,
> +					&slot))
> +			goto unlock;
> +		if (*slot != entry)
> +			goto unlock;
> +		radix_tree_replace_slot(slot, NULL);
> +		mapping->nrshadows--;
> +		if (!node)
> +			goto unlock;
> +		workingset_node_shadows_dec(node);
> +		/*
> +		 * Don't track node without shadow entries.
> +		 *
> +		 * Avoid acquiring the list_lru lock if already untracked.
> +		 * The list_empty() test is safe as node->private_list is
> +		 * protected by mapping->tree_lock.
> +		 */
> +		if (!workingset_node_shadows(node) &&
> +		    !list_empty(&node->private_list))
> +			list_lru_del(&workingset_shadow_nodes,
> +					&node->private_list);
> +		__radix_tree_delete_node(&mapping->page_tree, node);
> +	}
>  unlock:
>  	spin_unlock_irq(&mapping->tree_lock);
>  }
> @@ -228,7 +237,8 @@ void truncate_inode_pages_range(struct address_space *mapping,
>  	int		i;
>  
>  	cleancache_invalidate_inode(mapping);
> -	if (mapping->nrpages == 0 && mapping->nrshadows == 0)
> +	if (mapping->nrpages == 0 && mapping->nrshadows == 0 &&
> +			mapping->nrdax == 0)
>  		return;
>  
>  	/* Offsets within partial pages */
> @@ -423,7 +433,7 @@ void truncate_inode_pages_final(struct address_space *mapping)
>  	smp_rmb();
>  	nrshadows = mapping->nrshadows;
>  
> -	if (nrpages || nrshadows) {
> +	if (nrpages || nrshadows || mapping->nrdax) {
>  		/*
>  		 * As truncation uses a lockless tree lookup, cycle
>  		 * the tree lock to make sure any ongoing tree
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 2aec424..8071956 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -46,6 +46,7 @@
>  #include <linux/oom.h>
>  #include <linux/prefetch.h>
>  #include <linux/printk.h>
> +#include <linux/dax.h>
>  
>  #include <asm/tlbflush.h>
>  #include <asm/div64.h>
> @@ -671,9 +672,15 @@ static int __remove_mapping(struct address_space *mapping, struct page *page,
>  		 * inode reclaim needs to empty out the radix tree or
>  		 * the nodes are lost.  Don't plant shadows behind its
>  		 * back.
> +		 *
> +		 * We also don't store shadows for DAX mappings because the
> +		 * only page cache pages found in these are zero pages
> +		 * covering holes, and because we don't want to mix DAX
> +		 * exceptional entries and shadow exceptional entries in the
> +		 * same page_tree.
>  		 */
>  		if (reclaimed && page_is_file_cache(page) &&
> -		    !mapping_exiting(mapping))
> +		    !mapping_exiting(mapping) && !dax_mapping(mapping))
>  			shadow = workingset_eviction(mapping, page);
>  		__delete_from_page_cache(page, shadow, memcg);
>  		spin_unlock_irqrestore(&mapping->tree_lock, flags);
> -- 
> 2.5.0
> 
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

_______________________________________________
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http://oss.sgi.com/mailman/listinfo/xfs

Re: [PATCH v5 5/7] ext2: call dax_pfn_mkwrite() for DAX fsync/msync

[Jan Kara]

On Fri 18-12-15 22:22:18, Ross Zwisler wrote:
> To properly support the new DAX fsync/msync infrastructure filesystems
> need to call dax_pfn_mkwrite() so that DAX can track when user pages are
> dirtied.

The patch looks good to me. You can add:

Reviewed-by: Jan Kara <jack@suse.cz>

								Honza

> 
> Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
> ---
>  fs/ext2/file.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/ext2/file.c b/fs/ext2/file.c
> index 11a42c5..2c88d68 100644
> --- a/fs/ext2/file.c
> +++ b/fs/ext2/file.c
> @@ -102,8 +102,8 @@ static int ext2_dax_pfn_mkwrite(struct vm_area_struct *vma,
>  {
>  	struct inode *inode = file_inode(vma->vm_file);
>  	struct ext2_inode_info *ei = EXT2_I(inode);
> -	int ret = VM_FAULT_NOPAGE;
>  	loff_t size;
> +	int ret;
>  
>  	sb_start_pagefault(inode->i_sb);
>  	file_update_time(vma->vm_file);
> @@ -113,6 +113,8 @@ static int ext2_dax_pfn_mkwrite(struct vm_area_struct *vma,
>  	size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
>  	if (vmf->pgoff >= size)
>  		ret = VM_FAULT_SIGBUS;
> +	else
> +		ret = dax_pfn_mkwrite(vma, vmf);
>  
>  	up_read(&ei->dax_sem);
>  	sb_end_pagefault(inode->i_sb);
> -- 
> 2.5.0
> 
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

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Re: [PATCH v5 5/7] ext2: call dax_pfn_mkwrite() for DAX fsync/msync

[Jan Kara]

On Fri 18-12-15 22:22:18, Ross Zwisler wrote:
> To properly support the new DAX fsync/msync infrastructure filesystems
> need to call dax_pfn_mkwrite() so that DAX can track when user pages are
> dirtied.

The patch looks good to me. You can add:

Reviewed-by: Jan Kara <jack@suse.cz>

								Honza

> 
> Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
> ---
>  fs/ext2/file.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/ext2/file.c b/fs/ext2/file.c
> index 11a42c5..2c88d68 100644
> --- a/fs/ext2/file.c
> +++ b/fs/ext2/file.c
> @@ -102,8 +102,8 @@ static int ext2_dax_pfn_mkwrite(struct vm_area_struct *vma,
>  {
>  	struct inode *inode = file_inode(vma->vm_file);
>  	struct ext2_inode_info *ei = EXT2_I(inode);
> -	int ret = VM_FAULT_NOPAGE;
>  	loff_t size;
> +	int ret;
>  
>  	sb_start_pagefault(inode->i_sb);
>  	file_update_time(vma->vm_file);
> @@ -113,6 +113,8 @@ static int ext2_dax_pfn_mkwrite(struct vm_area_struct *vma,
>  	size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
>  	if (vmf->pgoff >= size)
>  		ret = VM_FAULT_SIGBUS;
> +	else
> +		ret = dax_pfn_mkwrite(vma, vmf);
>  
>  	up_read(&ei->dax_sem);
>  	sb_end_pagefault(inode->i_sb);
> -- 
> 2.5.0
> 
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

Re: [PATCH v5 5/7] ext2: call dax_pfn_mkwrite() for DAX fsync/msync

[Jan Kara]

On Fri 18-12-15 22:22:18, Ross Zwisler wrote:
> To properly support the new DAX fsync/msync infrastructure filesystems
> need to call dax_pfn_mkwrite() so that DAX can track when user pages are
> dirtied.

The patch looks good to me. You can add:

Reviewed-by: Jan Kara <jack@suse.cz>

								Honza

> 
> Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
> ---
>  fs/ext2/file.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/ext2/file.c b/fs/ext2/file.c
> index 11a42c5..2c88d68 100644
> --- a/fs/ext2/file.c
> +++ b/fs/ext2/file.c
> @@ -102,8 +102,8 @@ static int ext2_dax_pfn_mkwrite(struct vm_area_struct *vma,
>  {
>  	struct inode *inode = file_inode(vma->vm_file);
>  	struct ext2_inode_info *ei = EXT2_I(inode);
> -	int ret = VM_FAULT_NOPAGE;
>  	loff_t size;
> +	int ret;
>  
>  	sb_start_pagefault(inode->i_sb);
>  	file_update_time(vma->vm_file);
> @@ -113,6 +113,8 @@ static int ext2_dax_pfn_mkwrite(struct vm_area_struct *vma,
>  	size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
>  	if (vmf->pgoff >= size)
>  		ret = VM_FAULT_SIGBUS;
> +	else
> +		ret = dax_pfn_mkwrite(vma, vmf);
>  
>  	up_read(&ei->dax_sem);
>  	sb_end_pagefault(inode->i_sb);
> -- 
> 2.5.0
> 
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

Re: [PATCH v5 5/7] ext2: call dax_pfn_mkwrite() for DAX fsync/msync

[Jan Kara]

On Fri 18-12-15 22:22:18, Ross Zwisler wrote:
> To properly support the new DAX fsync/msync infrastructure filesystems
> need to call dax_pfn_mkwrite() so that DAX can track when user pages are
> dirtied.

The patch looks good to me. You can add:

Reviewed-by: Jan Kara <jack@suse.cz>

								Honza

> 
> Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
> ---
>  fs/ext2/file.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/ext2/file.c b/fs/ext2/file.c
> index 11a42c5..2c88d68 100644
> --- a/fs/ext2/file.c
> +++ b/fs/ext2/file.c
> @@ -102,8 +102,8 @@ static int ext2_dax_pfn_mkwrite(struct vm_area_struct *vma,
>  {
>  	struct inode *inode = file_inode(vma->vm_file);
>  	struct ext2_inode_info *ei = EXT2_I(inode);
> -	int ret = VM_FAULT_NOPAGE;
>  	loff_t size;
> +	int ret;
>  
>  	sb_start_pagefault(inode->i_sb);
>  	file_update_time(vma->vm_file);
> @@ -113,6 +113,8 @@ static int ext2_dax_pfn_mkwrite(struct vm_area_struct *vma,
>  	size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
>  	if (vmf->pgoff >= size)
>  		ret = VM_FAULT_SIGBUS;
> +	else
> +		ret = dax_pfn_mkwrite(vma, vmf);
>  
>  	up_read(&ei->dax_sem);
>  	sb_end_pagefault(inode->i_sb);
> -- 
> 2.5.0
> 
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

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Re: [PATCH v5 6/7] ext4: call dax_pfn_mkwrite() for DAX fsync/msync

[Jan Kara]

On Fri 18-12-15 22:22:19, Ross Zwisler wrote:
> To properly support the new DAX fsync/msync infrastructure filesystems
> need to call dax_pfn_mkwrite() so that DAX can track when user pages are
> dirtied.

The patch looks good to me. You can add:

Reviewed-by: Jan Kara <jack@suse.cz>

								Honza

> 
> Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
> ---
>  fs/ext4/file.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/ext4/file.c b/fs/ext4/file.c
> index 749b222..8c8965c 100644
> --- a/fs/ext4/file.c
> +++ b/fs/ext4/file.c
> @@ -291,8 +291,8 @@ static int ext4_dax_pfn_mkwrite(struct vm_area_struct *vma,
>  {
>  	struct inode *inode = file_inode(vma->vm_file);
>  	struct super_block *sb = inode->i_sb;
> -	int ret = VM_FAULT_NOPAGE;
>  	loff_t size;
> +	int ret;
>  
>  	sb_start_pagefault(sb);
>  	file_update_time(vma->vm_file);
> @@ -300,6 +300,8 @@ static int ext4_dax_pfn_mkwrite(struct vm_area_struct *vma,
>  	size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
>  	if (vmf->pgoff >= size)
>  		ret = VM_FAULT_SIGBUS;
> +	else
> +		ret = dax_pfn_mkwrite(vma, vmf);
>  	up_read(&EXT4_I(inode)->i_mmap_sem);
>  	sb_end_pagefault(sb);
>  
> -- 
> 2.5.0
> 
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
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Re: [PATCH v5 6/7] ext4: call dax_pfn_mkwrite() for DAX fsync/msync

[Jan Kara]

On Fri 18-12-15 22:22:19, Ross Zwisler wrote:
> To properly support the new DAX fsync/msync infrastructure filesystems
> need to call dax_pfn_mkwrite() so that DAX can track when user pages are
> dirtied.

The patch looks good to me. You can add:

Reviewed-by: Jan Kara <jack@suse.cz>

								Honza

> 
> Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
> ---
>  fs/ext4/file.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/ext4/file.c b/fs/ext4/file.c
> index 749b222..8c8965c 100644
> --- a/fs/ext4/file.c
> +++ b/fs/ext4/file.c
> @@ -291,8 +291,8 @@ static int ext4_dax_pfn_mkwrite(struct vm_area_struct *vma,
>  {
>  	struct inode *inode = file_inode(vma->vm_file);
>  	struct super_block *sb = inode->i_sb;
> -	int ret = VM_FAULT_NOPAGE;
>  	loff_t size;
> +	int ret;
>  
>  	sb_start_pagefault(sb);
>  	file_update_time(vma->vm_file);
> @@ -300,6 +300,8 @@ static int ext4_dax_pfn_mkwrite(struct vm_area_struct *vma,
>  	size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
>  	if (vmf->pgoff >= size)
>  		ret = VM_FAULT_SIGBUS;
> +	else
> +		ret = dax_pfn_mkwrite(vma, vmf);
>  	up_read(&EXT4_I(inode)->i_mmap_sem);
>  	sb_end_pagefault(sb);
>  
> -- 
> 2.5.0
> 
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

Re: [PATCH v5 6/7] ext4: call dax_pfn_mkwrite() for DAX fsync/msync

[Jan Kara]

On Fri 18-12-15 22:22:19, Ross Zwisler wrote:
> To properly support the new DAX fsync/msync infrastructure filesystems
> need to call dax_pfn_mkwrite() so that DAX can track when user pages are
> dirtied.

The patch looks good to me. You can add:

Reviewed-by: Jan Kara <jack@suse.cz>

								Honza

> 
> Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
> ---
>  fs/ext4/file.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/ext4/file.c b/fs/ext4/file.c
> index 749b222..8c8965c 100644
> --- a/fs/ext4/file.c
> +++ b/fs/ext4/file.c
> @@ -291,8 +291,8 @@ static int ext4_dax_pfn_mkwrite(struct vm_area_struct *vma,
>  {
>  	struct inode *inode = file_inode(vma->vm_file);
>  	struct super_block *sb = inode->i_sb;
> -	int ret = VM_FAULT_NOPAGE;
>  	loff_t size;
> +	int ret;
>  
>  	sb_start_pagefault(sb);
>  	file_update_time(vma->vm_file);
> @@ -300,6 +300,8 @@ static int ext4_dax_pfn_mkwrite(struct vm_area_struct *vma,
>  	size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
>  	if (vmf->pgoff >= size)
>  		ret = VM_FAULT_SIGBUS;
> +	else
> +		ret = dax_pfn_mkwrite(vma, vmf);
>  	up_read(&EXT4_I(inode)->i_mmap_sem);
>  	sb_end_pagefault(sb);
>  
> -- 
> 2.5.0
> 
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

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Re: [PATCH v5 2/7] dax: support dirty DAX entries in radix tree

[Ross Zwisler]

On Mon, Dec 21, 2015 at 06:15:12PM +0100, Jan Kara wrote:
> On Fri 18-12-15 22:22:15, Ross Zwisler wrote:
> > Add support for tracking dirty DAX entries in the struct address_space
> > radix tree.  This tree is already used for dirty page writeback, and it
> > already supports the use of exceptional (non struct page*) entries.
> > 
> > In order to properly track dirty DAX pages we will insert new exceptional
> > entries into the radix tree that represent dirty DAX PTE or PMD pages.
> > These exceptional entries will also contain the writeback addresses for the
> > PTE or PMD faults that we can use at fsync/msync time.
> > 
> > There are currently two types of exceptional entries (shmem and shadow)
> > that can be placed into the radix tree, and this adds a third.  We rely on
> > the fact that only one type of exceptional entry can be found in a given
> > radix tree based on its usage.  This happens for free with DAX vs shmem but
> > we explicitly prevent shadow entries from being added to radix trees for
> > DAX mappings.
> > 
> > The only shadow entries that would be generated for DAX radix trees would
> > be to track zero page mappings that were created for holes.  These pages
> > would receive minimal benefit from having shadow entries, and the choice
> > to have only one type of exceptional entry in a given radix tree makes the
> > logic simpler both in clear_exceptional_entry() and in the rest of DAX.
> > 
> > Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
> 
> The patch looks good to me. Just one comment: When we have this exclusion
> between different types of exceptional entries, there is no real need to
> have separate counters of 'shadow' and 'dax' entries, is there? We can have
> one 'nrexceptional' counter and don't have to grow struct inode
> unnecessarily which would be really welcome since DAX isn't a mainstream
> feature. Could you please change the code? Thanks!

Sure, this sounds good.  Thanks!

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Re: [PATCH v5 2/7] dax: support dirty DAX entries in radix tree

[Ross Zwisler]

On Mon, Dec 21, 2015 at 06:15:12PM +0100, Jan Kara wrote:
> On Fri 18-12-15 22:22:15, Ross Zwisler wrote:
> > Add support for tracking dirty DAX entries in the struct address_space
> > radix tree.  This tree is already used for dirty page writeback, and it
> > already supports the use of exceptional (non struct page*) entries.
> > 
> > In order to properly track dirty DAX pages we will insert new exceptional
> > entries into the radix tree that represent dirty DAX PTE or PMD pages.
> > These exceptional entries will also contain the writeback addresses for the
> > PTE or PMD faults that we can use at fsync/msync time.
> > 
> > There are currently two types of exceptional entries (shmem and shadow)
> > that can be placed into the radix tree, and this adds a third.  We rely on
> > the fact that only one type of exceptional entry can be found in a given
> > radix tree based on its usage.  This happens for free with DAX vs shmem but
> > we explicitly prevent shadow entries from being added to radix trees for
> > DAX mappings.
> > 
> > The only shadow entries that would be generated for DAX radix trees would
> > be to track zero page mappings that were created for holes.  These pages
> > would receive minimal benefit from having shadow entries, and the choice
> > to have only one type of exceptional entry in a given radix tree makes the
> > logic simpler both in clear_exceptional_entry() and in the rest of DAX.
> > 
> > Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
> 
> The patch looks good to me. Just one comment: When we have this exclusion
> between different types of exceptional entries, there is no real need to
> have separate counters of 'shadow' and 'dax' entries, is there? We can have
> one 'nrexceptional' counter and don't have to grow struct inode
> unnecessarily which would be really welcome since DAX isn't a mainstream
> feature. Could you please change the code? Thanks!

Sure, this sounds good.  Thanks!

Re: [PATCH v5 2/7] dax: support dirty DAX entries in radix tree

[Ross Zwisler]

On Mon, Dec 21, 2015 at 06:15:12PM +0100, Jan Kara wrote:
> On Fri 18-12-15 22:22:15, Ross Zwisler wrote:
> > Add support for tracking dirty DAX entries in the struct address_space
> > radix tree.  This tree is already used for dirty page writeback, and it
> > already supports the use of exceptional (non struct page*) entries.
> > 
> > In order to properly track dirty DAX pages we will insert new exceptional
> > entries into the radix tree that represent dirty DAX PTE or PMD pages.
> > These exceptional entries will also contain the writeback addresses for the
> > PTE or PMD faults that we can use at fsync/msync time.
> > 
> > There are currently two types of exceptional entries (shmem and shadow)
> > that can be placed into the radix tree, and this adds a third.  We rely on
> > the fact that only one type of exceptional entry can be found in a given
> > radix tree based on its usage.  This happens for free with DAX vs shmem but
> > we explicitly prevent shadow entries from being added to radix trees for
> > DAX mappings.
> > 
> > The only shadow entries that would be generated for DAX radix trees would
> > be to track zero page mappings that were created for holes.  These pages
> > would receive minimal benefit from having shadow entries, and the choice
> > to have only one type of exceptional entry in a given radix tree makes the
> > logic simpler both in clear_exceptional_entry() and in the rest of DAX.
> > 
> > Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
> 
> The patch looks good to me. Just one comment: When we have this exclusion
> between different types of exceptional entries, there is no real need to
> have separate counters of 'shadow' and 'dax' entries, is there? We can have
> one 'nrexceptional' counter and don't have to grow struct inode
> unnecessarily which would be really welcome since DAX isn't a mainstream
> feature. Could you please change the code? Thanks!

Sure, this sounds good.  Thanks!

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Re: [PATCH v5 4/7] dax: add support for fsync/sync

[Dan Williams]

On Mon, Dec 21, 2015 at 9:05 AM, Ross Zwisler
<ross.zwisler@linux.intel.com> wrote:
> On Sat, Dec 19, 2015 at 10:37:46AM -0800, Dan Williams wrote:
>> On Fri, Dec 18, 2015 at 9:22 PM, Ross Zwisler
>> <ross.zwisler@linux.intel.com> wrote:
[..]
>> Hi Ross, I should have realized this sooner, but what guarantees that
>> the address returned by RADIX_DAX_ADDR(entry) is still valid at this
>> point?  I think we need to store the sector in the radix tree and then
>> perform a new dax_map_atomic() operation to either lookup a valid
>> address or fail the sync request.  Otherwise, if the device is gone
>> we'll crash, or write into some other random vmalloc address space.
>
> Ah, good point, thank you.  v4 of this series is based on a version of
> DAX where we aren't properly dealing with PMEM device removal.  I've got an
> updated version that merges with your dax_map_atomic() changes, and I'll add
> this change into v5 which I will send out today.  Thank you for the
> suggestion.
>
> One clarification, with the code as it is in v4 we are only doing
> clflush/clflushopt/clwb instructions on the kaddr we've stored in the radix
> tree, so I don't think that there is actually a risk of us doing a "write into
> some other random vmalloc address space"?  I think at worse we will end up
> clflushing an address that either isn't mapped or has been remapped by someone
> else.  Or are you worried that the clflush would trigger a cache writeback to
> a memory address where writes have side effects, thus triggering the side
> effect?
>
> I definitely think it needs to be fixed, I'm just trying to make sure I
> understood your comment.

True, this would be flushing an address that was dirtied while valid.
Should be ok in practice for now since dax is effectively limited to
x86, but we should not be leaning on x86 details in an architecture
generic implementation like this.

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Re: [PATCH v5 4/7] dax: add support for fsync/sync

[Dan Williams]

On Mon, Dec 21, 2015 at 9:05 AM, Ross Zwisler
<ross.zwisler@linux.intel.com> wrote:
> On Sat, Dec 19, 2015 at 10:37:46AM -0800, Dan Williams wrote:
>> On Fri, Dec 18, 2015 at 9:22 PM, Ross Zwisler
>> <ross.zwisler@linux.intel.com> wrote:
[..]
>> Hi Ross, I should have realized this sooner, but what guarantees that
>> the address returned by RADIX_DAX_ADDR(entry) is still valid at this
>> point?  I think we need to store the sector in the radix tree and then
>> perform a new dax_map_atomic() operation to either lookup a valid
>> address or fail the sync request.  Otherwise, if the device is gone
>> we'll crash, or write into some other random vmalloc address space.
>
> Ah, good point, thank you.  v4 of this series is based on a version of
> DAX where we aren't properly dealing with PMEM device removal.  I've got an
> updated version that merges with your dax_map_atomic() changes, and I'll add
> this change into v5 which I will send out today.  Thank you for the
> suggestion.
>
> One clarification, with the code as it is in v4 we are only doing
> clflush/clflushopt/clwb instructions on the kaddr we've stored in the radix
> tree, so I don't think that there is actually a risk of us doing a "write into
> some other random vmalloc address space"?  I think at worse we will end up
> clflushing an address that either isn't mapped or has been remapped by someone
> else.  Or are you worried that the clflush would trigger a cache writeback to
> a memory address where writes have side effects, thus triggering the side
> effect?
>
> I definitely think it needs to be fixed, I'm just trying to make sure I
> understood your comment.

True, this would be flushing an address that was dirtied while valid.
Should be ok in practice for now since dax is effectively limited to
x86, but we should not be leaning on x86 details in an architecture
generic implementation like this.

Re: [PATCH v5 4/7] dax: add support for fsync/sync

[Dan Williams]

On Mon, Dec 21, 2015 at 9:05 AM, Ross Zwisler
<ross.zwisler@linux.intel.com> wrote:
> On Sat, Dec 19, 2015 at 10:37:46AM -0800, Dan Williams wrote:
>> On Fri, Dec 18, 2015 at 9:22 PM, Ross Zwisler
>> <ross.zwisler@linux.intel.com> wrote:
[..]
>> Hi Ross, I should have realized this sooner, but what guarantees that
>> the address returned by RADIX_DAX_ADDR(entry) is still valid at this
>> point?  I think we need to store the sector in the radix tree and then
>> perform a new dax_map_atomic() operation to either lookup a valid
>> address or fail the sync request.  Otherwise, if the device is gone
>> we'll crash, or write into some other random vmalloc address space.
>
> Ah, good point, thank you.  v4 of this series is based on a version of
> DAX where we aren't properly dealing with PMEM device removal.  I've got an
> updated version that merges with your dax_map_atomic() changes, and I'll add
> this change into v5 which I will send out today.  Thank you for the
> suggestion.
>
> One clarification, with the code as it is in v4 we are only doing
> clflush/clflushopt/clwb instructions on the kaddr we've stored in the radix
> tree, so I don't think that there is actually a risk of us doing a "write into
> some other random vmalloc address space"?  I think at worse we will end up
> clflushing an address that either isn't mapped or has been remapped by someone
> else.  Or are you worried that the clflush would trigger a cache writeback to
> a memory address where writes have side effects, thus triggering the side
> effect?
>
> I definitely think it needs to be fixed, I'm just trying to make sure I
> understood your comment.

True, this would be flushing an address that was dirtied while valid.
Should be ok in practice for now since dax is effectively limited to
x86, but we should not be leaning on x86 details in an architecture
generic implementation like this.

Re: [PATCH v5 4/7] dax: add support for fsync/sync

[Dan Williams]

On Mon, Dec 21, 2015 at 9:05 AM, Ross Zwisler
<ross.zwisler@linux.intel.com> wrote:
> On Sat, Dec 19, 2015 at 10:37:46AM -0800, Dan Williams wrote:
>> On Fri, Dec 18, 2015 at 9:22 PM, Ross Zwisler
>> <ross.zwisler@linux.intel.com> wrote:
[..]
>> Hi Ross, I should have realized this sooner, but what guarantees that
>> the address returned by RADIX_DAX_ADDR(entry) is still valid at this
>> point?  I think we need to store the sector in the radix tree and then
>> perform a new dax_map_atomic() operation to either lookup a valid
>> address or fail the sync request.  Otherwise, if the device is gone
>> we'll crash, or write into some other random vmalloc address space.
>
> Ah, good point, thank you.  v4 of this series is based on a version of
> DAX where we aren't properly dealing with PMEM device removal.  I've got an
> updated version that merges with your dax_map_atomic() changes, and I'll add
> this change into v5 which I will send out today.  Thank you for the
> suggestion.
>
> One clarification, with the code as it is in v4 we are only doing
> clflush/clflushopt/clwb instructions on the kaddr we've stored in the radix
> tree, so I don't think that there is actually a risk of us doing a "write into
> some other random vmalloc address space"?  I think at worse we will end up
> clflushing an address that either isn't mapped or has been remapped by someone
> else.  Or are you worried that the clflush would trigger a cache writeback to
> a memory address where writes have side effects, thus triggering the side
> effect?
>
> I definitely think it needs to be fixed, I'm just trying to make sure I
> understood your comment.

True, this would be flushing an address that was dirtied while valid.
Should be ok in practice for now since dax is effectively limited to
x86, but we should not be leaning on x86 details in an architecture
generic implementation like this.

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Re: [PATCH v5 4/7] dax: add support for fsync/sync

[Dan Williams]

On Mon, Dec 21, 2015 at 9:05 AM, Ross Zwisler
<ross.zwisler@linux.intel.com> wrote:
> On Sat, Dec 19, 2015 at 10:37:46AM -0800, Dan Williams wrote:
>> On Fri, Dec 18, 2015 at 9:22 PM, Ross Zwisler
>> <ross.zwisler@linux.intel.com> wrote:
>> > To properly handle fsync/msync in an efficient way DAX needs to track dirty
>> > pages so it is able to flush them durably to media on demand.
>> >
>> > The tracking of dirty pages is done via the radix tree in struct
>> > address_space.  This radix tree is already used by the page writeback
>> > infrastructure for tracking dirty pages associated with an open file, and
>> > it already has support for exceptional (non struct page*) entries.  We
>> > build upon these features to add exceptional entries to the radix tree for
>> > DAX dirty PMD or PTE pages at fault time.
>> >
>> > Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
>> [..]
>> > +static void dax_writeback_one(struct address_space *mapping, pgoff_t index,
>> > +               void *entry)
>> > +{
>> > +       struct radix_tree_root *page_tree = &mapping->page_tree;
>> > +       int type = RADIX_DAX_TYPE(entry);
>> > +       struct radix_tree_node *node;
>> > +       void **slot;
>> > +
>> > +       if (type != RADIX_DAX_PTE && type != RADIX_DAX_PMD) {
>> > +               WARN_ON_ONCE(1);
>> > +               return;
>> > +       }
>> > +
>> > +       spin_lock_irq(&mapping->tree_lock);
>> > +       /*
>> > +        * Regular page slots are stabilized by the page lock even
>> > +        * without the tree itself locked.  These unlocked entries
>> > +        * need verification under the tree lock.
>> > +        */
>> > +       if (!__radix_tree_lookup(page_tree, index, &node, &slot))
>> > +               goto unlock;
>> > +       if (*slot != entry)
>> > +               goto unlock;
>> > +
>> > +       /* another fsync thread may have already written back this entry */
>> > +       if (!radix_tree_tag_get(page_tree, index, PAGECACHE_TAG_TOWRITE))
>> > +               goto unlock;
>> > +
>> > +       radix_tree_tag_clear(page_tree, index, PAGECACHE_TAG_TOWRITE);
>> > +
>> > +       if (type == RADIX_DAX_PMD)
>> > +               wb_cache_pmem(RADIX_DAX_ADDR(entry), PMD_SIZE);
>> > +       else
>> > +               wb_cache_pmem(RADIX_DAX_ADDR(entry), PAGE_SIZE);
>>
>> Hi Ross, I should have realized this sooner, but what guarantees that
>> the address returned by RADIX_DAX_ADDR(entry) is still valid at this
>> point?  I think we need to store the sector in the radix tree and then
>> perform a new dax_map_atomic() operation to either lookup a valid
>> address or fail the sync request.  Otherwise, if the device is gone
>> we'll crash, or write into some other random vmalloc address space.
>
> Ah, good point, thank you.  v4 of this series is based on a version of
> DAX where we aren't properly dealing with PMEM device removal.  I've got an
> updated version that merges with your dax_map_atomic() changes, and I'll add
> this change into v5 which I will send out today.  Thank you for the
> suggestion.

To make the merge simpler you could skip the rebase for now and just
call blk_queue_enter() / blk_queue_exit() around the calls to
wb_cache_pmem.

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Re: [PATCH v5 4/7] dax: add support for fsync/sync

[Dan Williams]

On Mon, Dec 21, 2015 at 9:05 AM, Ross Zwisler
<ross.zwisler@linux.intel.com> wrote:
> On Sat, Dec 19, 2015 at 10:37:46AM -0800, Dan Williams wrote:
>> On Fri, Dec 18, 2015 at 9:22 PM, Ross Zwisler
>> <ross.zwisler@linux.intel.com> wrote:
>> > To properly handle fsync/msync in an efficient way DAX needs to track dirty
>> > pages so it is able to flush them durably to media on demand.
>> >
>> > The tracking of dirty pages is done via the radix tree in struct
>> > address_space.  This radix tree is already used by the page writeback
>> > infrastructure for tracking dirty pages associated with an open file, and
>> > it already has support for exceptional (non struct page*) entries.  We
>> > build upon these features to add exceptional entries to the radix tree for
>> > DAX dirty PMD or PTE pages at fault time.
>> >
>> > Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
>> [..]
>> > +static void dax_writeback_one(struct address_space *mapping, pgoff_t index,
>> > +               void *entry)
>> > +{
>> > +       struct radix_tree_root *page_tree = &mapping->page_tree;
>> > +       int type = RADIX_DAX_TYPE(entry);
>> > +       struct radix_tree_node *node;
>> > +       void **slot;
>> > +
>> > +       if (type != RADIX_DAX_PTE && type != RADIX_DAX_PMD) {
>> > +               WARN_ON_ONCE(1);
>> > +               return;
>> > +       }
>> > +
>> > +       spin_lock_irq(&mapping->tree_lock);
>> > +       /*
>> > +        * Regular page slots are stabilized by the page lock even
>> > +        * without the tree itself locked.  These unlocked entries
>> > +        * need verification under the tree lock.
>> > +        */
>> > +       if (!__radix_tree_lookup(page_tree, index, &node, &slot))
>> > +               goto unlock;
>> > +       if (*slot != entry)
>> > +               goto unlock;
>> > +
>> > +       /* another fsync thread may have already written back this entry */
>> > +       if (!radix_tree_tag_get(page_tree, index, PAGECACHE_TAG_TOWRITE))
>> > +               goto unlock;
>> > +
>> > +       radix_tree_tag_clear(page_tree, index, PAGECACHE_TAG_TOWRITE);
>> > +
>> > +       if (type == RADIX_DAX_PMD)
>> > +               wb_cache_pmem(RADIX_DAX_ADDR(entry), PMD_SIZE);
>> > +       else
>> > +               wb_cache_pmem(RADIX_DAX_ADDR(entry), PAGE_SIZE);
>>
>> Hi Ross, I should have realized this sooner, but what guarantees that
>> the address returned by RADIX_DAX_ADDR(entry) is still valid at this
>> point?  I think we need to store the sector in the radix tree and then
>> perform a new dax_map_atomic() operation to either lookup a valid
>> address or fail the sync request.  Otherwise, if the device is gone
>> we'll crash, or write into some other random vmalloc address space.
>
> Ah, good point, thank you.  v4 of this series is based on a version of
> DAX where we aren't properly dealing with PMEM device removal.  I've got an
> updated version that merges with your dax_map_atomic() changes, and I'll add
> this change into v5 which I will send out today.  Thank you for the
> suggestion.

To make the merge simpler you could skip the rebase for now and just
call blk_queue_enter() / blk_queue_exit() around the calls to
wb_cache_pmem.

Re: [PATCH v5 4/7] dax: add support for fsync/sync

[Dan Williams]

On Mon, Dec 21, 2015 at 9:05 AM, Ross Zwisler
<ross.zwisler@linux.intel.com> wrote:
> On Sat, Dec 19, 2015 at 10:37:46AM -0800, Dan Williams wrote:
>> On Fri, Dec 18, 2015 at 9:22 PM, Ross Zwisler
>> <ross.zwisler@linux.intel.com> wrote:
>> > To properly handle fsync/msync in an efficient way DAX needs to track dirty
>> > pages so it is able to flush them durably to media on demand.
>> >
>> > The tracking of dirty pages is done via the radix tree in struct
>> > address_space.  This radix tree is already used by the page writeback
>> > infrastructure for tracking dirty pages associated with an open file, and
>> > it already has support for exceptional (non struct page*) entries.  We
>> > build upon these features to add exceptional entries to the radix tree for
>> > DAX dirty PMD or PTE pages at fault time.
>> >
>> > Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
>> [..]
>> > +static void dax_writeback_one(struct address_space *mapping, pgoff_t index,
>> > +               void *entry)
>> > +{
>> > +       struct radix_tree_root *page_tree = &mapping->page_tree;
>> > +       int type = RADIX_DAX_TYPE(entry);
>> > +       struct radix_tree_node *node;
>> > +       void **slot;
>> > +
>> > +       if (type != RADIX_DAX_PTE && type != RADIX_DAX_PMD) {
>> > +               WARN_ON_ONCE(1);
>> > +               return;
>> > +       }
>> > +
>> > +       spin_lock_irq(&mapping->tree_lock);
>> > +       /*
>> > +        * Regular page slots are stabilized by the page lock even
>> > +        * without the tree itself locked.  These unlocked entries
>> > +        * need verification under the tree lock.
>> > +        */
>> > +       if (!__radix_tree_lookup(page_tree, index, &node, &slot))
>> > +               goto unlock;
>> > +       if (*slot != entry)
>> > +               goto unlock;
>> > +
>> > +       /* another fsync thread may have already written back this entry */
>> > +       if (!radix_tree_tag_get(page_tree, index, PAGECACHE_TAG_TOWRITE))
>> > +               goto unlock;
>> > +
>> > +       radix_tree_tag_clear(page_tree, index, PAGECACHE_TAG_TOWRITE);
>> > +
>> > +       if (type == RADIX_DAX_PMD)
>> > +               wb_cache_pmem(RADIX_DAX_ADDR(entry), PMD_SIZE);
>> > +       else
>> > +               wb_cache_pmem(RADIX_DAX_ADDR(entry), PAGE_SIZE);
>>
>> Hi Ross, I should have realized this sooner, but what guarantees that
>> the address returned by RADIX_DAX_ADDR(entry) is still valid at this
>> point?  I think we need to store the sector in the radix tree and then
>> perform a new dax_map_atomic() operation to either lookup a valid
>> address or fail the sync request.  Otherwise, if the device is gone
>> we'll crash, or write into some other random vmalloc address space.
>
> Ah, good point, thank you.  v4 of this series is based on a version of
> DAX where we aren't properly dealing with PMEM device removal.  I've got an
> updated version that merges with your dax_map_atomic() changes, and I'll add
> this change into v5 which I will send out today.  Thank you for the
> suggestion.

To make the merge simpler you could skip the rebase for now and just
call blk_queue_enter() / blk_queue_exit() around the calls to
wb_cache_pmem.

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Re: [PATCH v5 4/7] dax: add support for fsync/sync

[Dan Williams]

On Mon, Dec 21, 2015 at 9:05 AM, Ross Zwisler
<ross.zwisler@linux.intel.com> wrote:
> On Sat, Dec 19, 2015 at 10:37:46AM -0800, Dan Williams wrote:
>> On Fri, Dec 18, 2015 at 9:22 PM, Ross Zwisler
>> <ross.zwisler@linux.intel.com> wrote:
>> > To properly handle fsync/msync in an efficient way DAX needs to track dirty
>> > pages so it is able to flush them durably to media on demand.
>> >
>> > The tracking of dirty pages is done via the radix tree in struct
>> > address_space.  This radix tree is already used by the page writeback
>> > infrastructure for tracking dirty pages associated with an open file, and
>> > it already has support for exceptional (non struct page*) entries.  We
>> > build upon these features to add exceptional entries to the radix tree for
>> > DAX dirty PMD or PTE pages at fault time.
>> >
>> > Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
>> [..]
>> > +static void dax_writeback_one(struct address_space *mapping, pgoff_t index,
>> > +               void *entry)
>> > +{
>> > +       struct radix_tree_root *page_tree = &mapping->page_tree;
>> > +       int type = RADIX_DAX_TYPE(entry);
>> > +       struct radix_tree_node *node;
>> > +       void **slot;
>> > +
>> > +       if (type != RADIX_DAX_PTE && type != RADIX_DAX_PMD) {
>> > +               WARN_ON_ONCE(1);
>> > +               return;
>> > +       }
>> > +
>> > +       spin_lock_irq(&mapping->tree_lock);
>> > +       /*
>> > +        * Regular page slots are stabilized by the page lock even
>> > +        * without the tree itself locked.  These unlocked entries
>> > +        * need verification under the tree lock.
>> > +        */
>> > +       if (!__radix_tree_lookup(page_tree, index, &node, &slot))
>> > +               goto unlock;
>> > +       if (*slot != entry)
>> > +               goto unlock;
>> > +
>> > +       /* another fsync thread may have already written back this entry */
>> > +       if (!radix_tree_tag_get(page_tree, index, PAGECACHE_TAG_TOWRITE))
>> > +               goto unlock;
>> > +
>> > +       radix_tree_tag_clear(page_tree, index, PAGECACHE_TAG_TOWRITE);
>> > +
>> > +       if (type == RADIX_DAX_PMD)
>> > +               wb_cache_pmem(RADIX_DAX_ADDR(entry), PMD_SIZE);
>> > +       else
>> > +               wb_cache_pmem(RADIX_DAX_ADDR(entry), PAGE_SIZE);
>>
>> Hi Ross, I should have realized this sooner, but what guarantees that
>> the address returned by RADIX_DAX_ADDR(entry) is still valid at this
>> point?  I think we need to store the sector in the radix tree and then
>> perform a new dax_map_atomic() operation to either lookup a valid
>> address or fail the sync request.  Otherwise, if the device is gone
>> we'll crash, or write into some other random vmalloc address space.
>
> Ah, good point, thank you.  v4 of this series is based on a version of
> DAX where we aren't properly dealing with PMEM device removal.  I've got an
> updated version that merges with your dax_map_atomic() changes, and I'll add
> this change into v5 which I will send out today.  Thank you for the
> suggestion.

To make the merge simpler you could skip the rebase for now and just
call blk_queue_enter() / blk_queue_exit() around the calls to
wb_cache_pmem.

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Re: [PATCH v5 1/7] pmem: add wb_cache_pmem() to the PMEM API

[Andrew Morton]

On Fri, 18 Dec 2015 22:22:14 -0700 Ross Zwisler <ross.zwisler@linux.intel.com> wrote:

> The function __arch_wb_cache_pmem() was already an internal implementation
> detail of the x86 PMEM API, but this functionality needs to be exported as
> part of the general PMEM API to handle the fsync/msync case for DAX mmaps.
> 
> One thing worth noting is that we really do want this to be part of the
> PMEM API as opposed to a stand-alone function like clflush_cache_range()
> because of ordering restrictions.  By having wb_cache_pmem() as part of the
> PMEM API we can leave it unordered, call it multiple times to write back
> large amounts of memory, and then order the multiple calls with a single
> wmb_pmem().
> 
> @@ -138,7 +139,7 @@ static inline void arch_clear_pmem(void __pmem *addr, size_t size)
>  	else
>  		memset(vaddr, 0, size);
>  
> -	__arch_wb_cache_pmem(vaddr, size);
> +	arch_wb_cache_pmem(addr, size);
>  }
>  

reject.  I made this

	arch_wb_cache_pmem(vaddr, size);

due to Dan's
http://www.ozlabs.org/~akpm/mmots/broken-out/pmem-dax-clean-up-clear_pmem.patch

Re: [PATCH v5 1/7] pmem: add wb_cache_pmem() to the PMEM API

[Andrew Morton]

On Fri, 18 Dec 2015 22:22:14 -0700 Ross Zwisler <ross.zwisler@linux.intel.com> wrote:

> The function __arch_wb_cache_pmem() was already an internal implementation
> detail of the x86 PMEM API, but this functionality needs to be exported as
> part of the general PMEM API to handle the fsync/msync case for DAX mmaps.
> 
> One thing worth noting is that we really do want this to be part of the
> PMEM API as opposed to a stand-alone function like clflush_cache_range()
> because of ordering restrictions.  By having wb_cache_pmem() as part of the
> PMEM API we can leave it unordered, call it multiple times to write back
> large amounts of memory, and then order the multiple calls with a single
> wmb_pmem().
> 
> @@ -138,7 +139,7 @@ static inline void arch_clear_pmem(void __pmem *addr, size_t size)
>  	else
>  		memset(vaddr, 0, size);
>  
> -	__arch_wb_cache_pmem(vaddr, size);
> +	arch_wb_cache_pmem(addr, size);
>  }
>  

reject.  I made this

	arch_wb_cache_pmem(vaddr, size);

due to Dan's
http://www.ozlabs.org/~akpm/mmots/broken-out/pmem-dax-clean-up-clear_pmem.patch

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Re: [PATCH v5 1/7] pmem: add wb_cache_pmem() to the PMEM API

[Andrew Morton]

On Fri, 18 Dec 2015 22:22:14 -0700 Ross Zwisler <ross.zwisler@linux.intel.com> wrote:

> The function __arch_wb_cache_pmem() was already an internal implementation
> detail of the x86 PMEM API, but this functionality needs to be exported as
> part of the general PMEM API to handle the fsync/msync case for DAX mmaps.
> 
> One thing worth noting is that we really do want this to be part of the
> PMEM API as opposed to a stand-alone function like clflush_cache_range()
> because of ordering restrictions.  By having wb_cache_pmem() as part of the
> PMEM API we can leave it unordered, call it multiple times to write back
> large amounts of memory, and then order the multiple calls with a single
> wmb_pmem().
> 
> @@ -138,7 +139,7 @@ static inline void arch_clear_pmem(void __pmem *addr, size_t size)
>  	else
>  		memset(vaddr, 0, size);
>  
> -	__arch_wb_cache_pmem(vaddr, size);
> +	arch_wb_cache_pmem(addr, size);
>  }
>  

reject.  I made this

	arch_wb_cache_pmem(vaddr, size);

due to Dan's
http://www.ozlabs.org/~akpm/mmots/broken-out/pmem-dax-clean-up-clear_pmem.patch

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Re: [PATCH v5 2/7] dax: support dirty DAX entries in radix tree

[Andrew Morton]

On Fri, 18 Dec 2015 22:22:15 -0700 Ross Zwisler <ross.zwisler@linux.intel.com> wrote:

> Add support for tracking dirty DAX entries in the struct address_space
> radix tree.  This tree is already used for dirty page writeback, and it
> already supports the use of exceptional (non struct page*) entries.
> 
> In order to properly track dirty DAX pages we will insert new exceptional
> entries into the radix tree that represent dirty DAX PTE or PMD pages.
> These exceptional entries will also contain the writeback addresses for the
> PTE or PMD faults that we can use at fsync/msync time.
> 
> There are currently two types of exceptional entries (shmem and shadow)
> that can be placed into the radix tree, and this adds a third.  We rely on
> the fact that only one type of exceptional entry can be found in a given
> radix tree based on its usage.  This happens for free with DAX vs shmem but
> we explicitly prevent shadow entries from being added to radix trees for
> DAX mappings.
> 
> The only shadow entries that would be generated for DAX radix trees would
> be to track zero page mappings that were created for holes.  These pages
> would receive minimal benefit from having shadow entries, and the choice
> to have only one type of exceptional entry in a given radix tree makes the
> logic simpler both in clear_exceptional_entry() and in the rest of DAX.
> 
>
> ...
>
> --- a/include/linux/dax.h
> +++ b/include/linux/dax.h
> @@ -36,4 +36,9 @@ static inline bool vma_is_dax(struct vm_area_struct *vma)
>  {
>  	return vma->vm_file && IS_DAX(vma->vm_file->f_mapping->host);
>  }
> +
> +static inline bool dax_mapping(struct address_space *mapping)
> +{
> +	return mapping->host && IS_DAX(mapping->host);
> +}

Can we make this evaluate to plain old "0" when CONFIG_FS_DAX=n?  That
way a bunch of code in callers will fall away as well.

If the compiler has any brains then a good way to do this would be to
make IS_DAX be "0" but one would need to check that the zeroness
properly propagated out of the inline.

>  #endif
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 3aa5142..b9ac534 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -433,6 +433,7 @@ struct address_space {
>  	/* Protected by tree_lock together with the radix tree */
>  	unsigned long		nrpages;	/* number of total pages */
>  	unsigned long		nrshadows;	/* number of shadow entries */
> +	unsigned long		nrdax;	        /* number of DAX entries */

hm, that's unfortunate - machines commonly carry tremendous numbers of
address_spaces in memory and adding pork to them is rather a big deal. 
We can't avoid this somehow?  Maybe share the space with nrshadows by
some means?  Find some other field which is unused for dax files?

> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -11,6 +11,7 @@
>   */
>  #include <linux/export.h>
>  #include <linux/compiler.h>
> +#include <linux/dax.h>
>  #include <linux/fs.h>
>  #include <linux/uaccess.h>
>  #include <linux/capability.h>
> @@ -579,6 +580,12 @@ static int page_cache_tree_insert(struct address_space *mapping,
>  		p = radix_tree_deref_slot_protected(slot, &mapping->tree_lock);
>  		if (!radix_tree_exceptional_entry(p))
>  			return -EEXIST;
> +
> +		if (dax_mapping(mapping)) {
> +			WARN_ON(1);
> +			return -EINVAL;
> +		}

this:

--- a/mm/filemap.c~dax-support-dirty-dax-entries-in-radix-tree-fix
+++ a/mm/filemap.c
@@ -581,10 +581,8 @@ static int page_cache_tree_insert(struct
 		if (!radix_tree_exceptional_entry(p))
 			return -EEXIST;
 
-		if (dax_mapping(mapping)) {
-			WARN_ON(1);
+		if (WARN_ON(dax_mapping(mapping)))
 			return -EINVAL;
-		}
 
 		if (shadowp)
 			*shadowp = p;

Re: [PATCH v5 2/7] dax: support dirty DAX entries in radix tree

[Andrew Morton]

On Fri, 18 Dec 2015 22:22:15 -0700 Ross Zwisler <ross.zwisler@linux.intel.com> wrote:

> Add support for tracking dirty DAX entries in the struct address_space
> radix tree.  This tree is already used for dirty page writeback, and it
> already supports the use of exceptional (non struct page*) entries.
> 
> In order to properly track dirty DAX pages we will insert new exceptional
> entries into the radix tree that represent dirty DAX PTE or PMD pages.
> These exceptional entries will also contain the writeback addresses for the
> PTE or PMD faults that we can use at fsync/msync time.
> 
> There are currently two types of exceptional entries (shmem and shadow)
> that can be placed into the radix tree, and this adds a third.  We rely on
> the fact that only one type of exceptional entry can be found in a given
> radix tree based on its usage.  This happens for free with DAX vs shmem but
> we explicitly prevent shadow entries from being added to radix trees for
> DAX mappings.
> 
> The only shadow entries that would be generated for DAX radix trees would
> be to track zero page mappings that were created for holes.  These pages
> would receive minimal benefit from having shadow entries, and the choice
> to have only one type of exceptional entry in a given radix tree makes the
> logic simpler both in clear_exceptional_entry() and in the rest of DAX.
> 
>
> ...
>
> --- a/include/linux/dax.h
> +++ b/include/linux/dax.h
> @@ -36,4 +36,9 @@ static inline bool vma_is_dax(struct vm_area_struct *vma)
>  {
>  	return vma->vm_file && IS_DAX(vma->vm_file->f_mapping->host);
>  }
> +
> +static inline bool dax_mapping(struct address_space *mapping)
> +{
> +	return mapping->host && IS_DAX(mapping->host);
> +}

Can we make this evaluate to plain old "0" when CONFIG_FS_DAX=n?  That
way a bunch of code in callers will fall away as well.

If the compiler has any brains then a good way to do this would be to
make IS_DAX be "0" but one would need to check that the zeroness
properly propagated out of the inline.

>  #endif
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 3aa5142..b9ac534 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -433,6 +433,7 @@ struct address_space {
>  	/* Protected by tree_lock together with the radix tree */
>  	unsigned long		nrpages;	/* number of total pages */
>  	unsigned long		nrshadows;	/* number of shadow entries */
> +	unsigned long		nrdax;	        /* number of DAX entries */

hm, that's unfortunate - machines commonly carry tremendous numbers of
address_spaces in memory and adding pork to them is rather a big deal. 
We can't avoid this somehow?  Maybe share the space with nrshadows by
some means?  Find some other field which is unused for dax files?

> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -11,6 +11,7 @@
>   */
>  #include <linux/export.h>
>  #include <linux/compiler.h>
> +#include <linux/dax.h>
>  #include <linux/fs.h>
>  #include <linux/uaccess.h>
>  #include <linux/capability.h>
> @@ -579,6 +580,12 @@ static int page_cache_tree_insert(struct address_space *mapping,
>  		p = radix_tree_deref_slot_protected(slot, &mapping->tree_lock);
>  		if (!radix_tree_exceptional_entry(p))
>  			return -EEXIST;
> +
> +		if (dax_mapping(mapping)) {
> +			WARN_ON(1);
> +			return -EINVAL;
> +		}

this:

--- a/mm/filemap.c~dax-support-dirty-dax-entries-in-radix-tree-fix
+++ a/mm/filemap.c
@@ -581,10 +581,8 @@ static int page_cache_tree_insert(struct
 		if (!radix_tree_exceptional_entry(p))
 			return -EEXIST;
 
-		if (dax_mapping(mapping)) {
-			WARN_ON(1);
+		if (WARN_ON(dax_mapping(mapping)))
 			return -EINVAL;
-		}
 
 		if (shadowp)
 			*shadowp = p;


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Re: [PATCH v5 2/7] dax: support dirty DAX entries in radix tree

[Andrew Morton]

On Fri, 18 Dec 2015 22:22:15 -0700 Ross Zwisler <ross.zwisler@linux.intel.com> wrote:

> Add support for tracking dirty DAX entries in the struct address_space
> radix tree.  This tree is already used for dirty page writeback, and it
> already supports the use of exceptional (non struct page*) entries.
> 
> In order to properly track dirty DAX pages we will insert new exceptional
> entries into the radix tree that represent dirty DAX PTE or PMD pages.
> These exceptional entries will also contain the writeback addresses for the
> PTE or PMD faults that we can use at fsync/msync time.
> 
> There are currently two types of exceptional entries (shmem and shadow)
> that can be placed into the radix tree, and this adds a third.  We rely on
> the fact that only one type of exceptional entry can be found in a given
> radix tree based on its usage.  This happens for free with DAX vs shmem but
> we explicitly prevent shadow entries from being added to radix trees for
> DAX mappings.
> 
> The only shadow entries that would be generated for DAX radix trees would
> be to track zero page mappings that were created for holes.  These pages
> would receive minimal benefit from having shadow entries, and the choice
> to have only one type of exceptional entry in a given radix tree makes the
> logic simpler both in clear_exceptional_entry() and in the rest of DAX.
> 
>
> ...
>
> --- a/include/linux/dax.h
> +++ b/include/linux/dax.h
> @@ -36,4 +36,9 @@ static inline bool vma_is_dax(struct vm_area_struct *vma)
>  {
>  	return vma->vm_file && IS_DAX(vma->vm_file->f_mapping->host);
>  }
> +
> +static inline bool dax_mapping(struct address_space *mapping)
> +{
> +	return mapping->host && IS_DAX(mapping->host);
> +}

Can we make this evaluate to plain old "0" when CONFIG_FS_DAX=n?  That
way a bunch of code in callers will fall away as well.

If the compiler has any brains then a good way to do this would be to
make IS_DAX be "0" but one would need to check that the zeroness
properly propagated out of the inline.

>  #endif
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 3aa5142..b9ac534 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -433,6 +433,7 @@ struct address_space {
>  	/* Protected by tree_lock together with the radix tree */
>  	unsigned long		nrpages;	/* number of total pages */
>  	unsigned long		nrshadows;	/* number of shadow entries */
> +	unsigned long		nrdax;	        /* number of DAX entries */

hm, that's unfortunate - machines commonly carry tremendous numbers of
address_spaces in memory and adding pork to them is rather a big deal. 
We can't avoid this somehow?  Maybe share the space with nrshadows by
some means?  Find some other field which is unused for dax files?

> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -11,6 +11,7 @@
>   */
>  #include <linux/export.h>
>  #include <linux/compiler.h>
> +#include <linux/dax.h>
>  #include <linux/fs.h>
>  #include <linux/uaccess.h>
>  #include <linux/capability.h>
> @@ -579,6 +580,12 @@ static int page_cache_tree_insert(struct address_space *mapping,
>  		p = radix_tree_deref_slot_protected(slot, &mapping->tree_lock);
>  		if (!radix_tree_exceptional_entry(p))
>  			return -EEXIST;
> +
> +		if (dax_mapping(mapping)) {
> +			WARN_ON(1);
> +			return -EINVAL;
> +		}

this:

--- a/mm/filemap.c~dax-support-dirty-dax-entries-in-radix-tree-fix
+++ a/mm/filemap.c
@@ -581,10 +581,8 @@ static int page_cache_tree_insert(struct
 		if (!radix_tree_exceptional_entry(p))
 			return -EEXIST;
 
-		if (dax_mapping(mapping)) {
-			WARN_ON(1);
+		if (WARN_ON(dax_mapping(mapping)))
 			return -EINVAL;
-		}
 
 		if (shadowp)
 			*shadowp = p;


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Re: [PATCH v5 3/7] mm: add find_get_entries_tag()

[Andrew Morton]

On Fri, 18 Dec 2015 22:22:16 -0700 Ross Zwisler <ross.zwisler@linux.intel.com> wrote:

> Add find_get_entries_tag() to the family of functions that include
> find_get_entries(), find_get_pages() and find_get_pages_tag().  This is
> needed for DAX dirty page handling because we need a list of both page
> offsets and radix tree entries ('indices' and 'entries' in this function)
> that are marked with the PAGECACHE_TAG_TOWRITE tag.
> 
> ...
>
> +EXPORT_SYMBOL(find_get_entries_tag);

This is actually a pretty crappy name because it doesn't describe what
subsystem it belongs to.  scheduler?  scatter/gather?  filesystem?

But given what we've already done, I don't see an obvious fix.

Re: [PATCH v5 3/7] mm: add find_get_entries_tag()

[Andrew Morton]

On Fri, 18 Dec 2015 22:22:16 -0700 Ross Zwisler <ross.zwisler@linux.intel.com> wrote:

> Add find_get_entries_tag() to the family of functions that include
> find_get_entries(), find_get_pages() and find_get_pages_tag().  This is
> needed for DAX dirty page handling because we need a list of both page
> offsets and radix tree entries ('indices' and 'entries' in this function)
> that are marked with the PAGECACHE_TAG_TOWRITE tag.
> 
> ...
>
> +EXPORT_SYMBOL(find_get_entries_tag);

This is actually a pretty crappy name because it doesn't describe what
subsystem it belongs to.  scheduler?  scatter/gather?  filesystem?

But given what we've already done, I don't see an obvious fix.

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Re: [PATCH v5 3/7] mm: add find_get_entries_tag()

[Andrew Morton]

On Fri, 18 Dec 2015 22:22:16 -0700 Ross Zwisler <ross.zwisler@linux.intel.com> wrote:

> Add find_get_entries_tag() to the family of functions that include
> find_get_entries(), find_get_pages() and find_get_pages_tag().  This is
> needed for DAX dirty page handling because we need a list of both page
> offsets and radix tree entries ('indices' and 'entries' in this function)
> that are marked with the PAGECACHE_TAG_TOWRITE tag.
> 
> ...
>
> +EXPORT_SYMBOL(find_get_entries_tag);

This is actually a pretty crappy name because it doesn't describe what
subsystem it belongs to.  scheduler?  scatter/gather?  filesystem?

But given what we've already done, I don't see an obvious fix.

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Re: [PATCH v5 4/7] dax: add support for fsync/sync

[Andrew Morton]

On Fri, 18 Dec 2015 22:22:17 -0700 Ross Zwisler <ross.zwisler@linux.intel.com> wrote:

> To properly handle fsync/msync in an efficient way DAX needs to track dirty
> pages so it is able to flush them durably to media on demand.
> 
> The tracking of dirty pages is done via the radix tree in struct
> address_space.  This radix tree is already used by the page writeback
> infrastructure for tracking dirty pages associated with an open file, and
> it already has support for exceptional (non struct page*) entries.  We
> build upon these features to add exceptional entries to the radix tree for
> DAX dirty PMD or PTE pages at fault time.

I'm getting a few rejects here against other pending changes.  Things
look OK to me but please do runtime test the end result as it resides
in linux-next.  Which will be next year.

>
> ...
>
> +static void dax_writeback_one(struct address_space *mapping, pgoff_t index,
> +		void *entry)
> +{
> +	struct radix_tree_root *page_tree = &mapping->page_tree;
> +	int type = RADIX_DAX_TYPE(entry);
> +	struct radix_tree_node *node;
> +	void **slot;
> +
> +	if (type != RADIX_DAX_PTE && type != RADIX_DAX_PMD) {
> +		WARN_ON_ONCE(1);
> +		return;
> +	}

--- a/fs/dax.c~dax-add-support-for-fsync-sync-fix
+++ a/fs/dax.c
@@ -383,10 +383,8 @@ static void dax_writeback_one(struct add
 	struct radix_tree_node *node;
 	void **slot;
 
-	if (type != RADIX_DAX_PTE && type != RADIX_DAX_PMD) {
-		WARN_ON_ONCE(1);
+	if (WARN_ON_ONCE(type != RADIX_DAX_PTE && type != RADIX_DAX_PMD))
 		return;
-	}
 
 	spin_lock_irq(&mapping->tree_lock);
 	/*

> +	spin_lock_irq(&mapping->tree_lock);
> +	/*
> +	 * Regular page slots are stabilized by the page lock even
> +	 * without the tree itself locked.  These unlocked entries
> +	 * need verification under the tree lock.
> +	 */
> +	if (!__radix_tree_lookup(page_tree, index, &node, &slot))
> +		goto unlock;
> +	if (*slot != entry)
> +		goto unlock;
> +
> +	/* another fsync thread may have already written back this entry */
> +	if (!radix_tree_tag_get(page_tree, index, PAGECACHE_TAG_TOWRITE))
> +		goto unlock;
> +
> +	radix_tree_tag_clear(page_tree, index, PAGECACHE_TAG_TOWRITE);
> +
> +	if (type == RADIX_DAX_PMD)
> +		wb_cache_pmem(RADIX_DAX_ADDR(entry), PMD_SIZE);
> +	else
> +		wb_cache_pmem(RADIX_DAX_ADDR(entry), PAGE_SIZE);
> + unlock:
> +	spin_unlock_irq(&mapping->tree_lock);
> +}
> +
> +/*
> + * Flush the mapping to the persistent domain within the byte range of [start,
> + * end]. This is required by data integrity operations to ensure file data is
> + * on persistent storage prior to completion of the operation.
> + */
> +void dax_writeback_mapping_range(struct address_space *mapping, loff_t start,
> +		loff_t end)
> +{
> +	struct inode *inode = mapping->host;
> +	pgoff_t indices[PAGEVEC_SIZE];
> +	pgoff_t start_page, end_page;
> +	struct pagevec pvec;
> +	void *entry;
> +	int i;
> +
> +	if (inode->i_blkbits != PAGE_SHIFT) {
> +		WARN_ON_ONCE(1);
> +		return;
> +	}

again

> +	rcu_read_lock();
> +	entry = radix_tree_lookup(&mapping->page_tree, start & PMD_MASK);
> +	rcu_read_unlock();

What stabilizes the memory at *entry after rcu_read_unlock()?

> +	/* see if the start of our range is covered by a PMD entry */
> +	if (entry && RADIX_DAX_TYPE(entry) == RADIX_DAX_PMD)
> +		start &= PMD_MASK;
> +
> +	start_page = start >> PAGE_CACHE_SHIFT;
> +	end_page = end >> PAGE_CACHE_SHIFT;
> +
> +	tag_pages_for_writeback(mapping, start_page, end_page);
> +
> +	pagevec_init(&pvec, 0);
> +	while (1) {
> +		pvec.nr = find_get_entries_tag(mapping, start_page,
> +				PAGECACHE_TAG_TOWRITE, PAGEVEC_SIZE,
> +				pvec.pages, indices);
> +
> +		if (pvec.nr == 0)
> +			break;
> +
> +		for (i = 0; i < pvec.nr; i++)
> +			dax_writeback_one(mapping, indices[i], pvec.pages[i]);
> +	}
> +	wmb_pmem();
> +}
> +EXPORT_SYMBOL_GPL(dax_writeback_mapping_range);
> +
>
> ...
>

Re: [PATCH v5 4/7] dax: add support for fsync/sync

[Andrew Morton]

On Fri, 18 Dec 2015 22:22:17 -0700 Ross Zwisler <ross.zwisler@linux.intel.com> wrote:

> To properly handle fsync/msync in an efficient way DAX needs to track dirty
> pages so it is able to flush them durably to media on demand.
> 
> The tracking of dirty pages is done via the radix tree in struct
> address_space.  This radix tree is already used by the page writeback
> infrastructure for tracking dirty pages associated with an open file, and
> it already has support for exceptional (non struct page*) entries.  We
> build upon these features to add exceptional entries to the radix tree for
> DAX dirty PMD or PTE pages at fault time.

I'm getting a few rejects here against other pending changes.  Things
look OK to me but please do runtime test the end result as it resides
in linux-next.  Which will be next year.

>
> ...
>
> +static void dax_writeback_one(struct address_space *mapping, pgoff_t index,
> +		void *entry)
> +{
> +	struct radix_tree_root *page_tree = &mapping->page_tree;
> +	int type = RADIX_DAX_TYPE(entry);
> +	struct radix_tree_node *node;
> +	void **slot;
> +
> +	if (type != RADIX_DAX_PTE && type != RADIX_DAX_PMD) {
> +		WARN_ON_ONCE(1);
> +		return;
> +	}

--- a/fs/dax.c~dax-add-support-for-fsync-sync-fix
+++ a/fs/dax.c
@@ -383,10 +383,8 @@ static void dax_writeback_one(struct add
 	struct radix_tree_node *node;
 	void **slot;
 
-	if (type != RADIX_DAX_PTE && type != RADIX_DAX_PMD) {
-		WARN_ON_ONCE(1);
+	if (WARN_ON_ONCE(type != RADIX_DAX_PTE && type != RADIX_DAX_PMD))
 		return;
-	}
 
 	spin_lock_irq(&mapping->tree_lock);
 	/*

> +	spin_lock_irq(&mapping->tree_lock);
> +	/*
> +	 * Regular page slots are stabilized by the page lock even
> +	 * without the tree itself locked.  These unlocked entries
> +	 * need verification under the tree lock.
> +	 */
> +	if (!__radix_tree_lookup(page_tree, index, &node, &slot))
> +		goto unlock;
> +	if (*slot != entry)
> +		goto unlock;
> +
> +	/* another fsync thread may have already written back this entry */
> +	if (!radix_tree_tag_get(page_tree, index, PAGECACHE_TAG_TOWRITE))
> +		goto unlock;
> +
> +	radix_tree_tag_clear(page_tree, index, PAGECACHE_TAG_TOWRITE);
> +
> +	if (type == RADIX_DAX_PMD)
> +		wb_cache_pmem(RADIX_DAX_ADDR(entry), PMD_SIZE);
> +	else
> +		wb_cache_pmem(RADIX_DAX_ADDR(entry), PAGE_SIZE);
> + unlock:
> +	spin_unlock_irq(&mapping->tree_lock);
> +}
> +
> +/*
> + * Flush the mapping to the persistent domain within the byte range of [start,
> + * end]. This is required by data integrity operations to ensure file data is
> + * on persistent storage prior to completion of the operation.
> + */
> +void dax_writeback_mapping_range(struct address_space *mapping, loff_t start,
> +		loff_t end)
> +{
> +	struct inode *inode = mapping->host;
> +	pgoff_t indices[PAGEVEC_SIZE];
> +	pgoff_t start_page, end_page;
> +	struct pagevec pvec;
> +	void *entry;
> +	int i;
> +
> +	if (inode->i_blkbits != PAGE_SHIFT) {
> +		WARN_ON_ONCE(1);
> +		return;
> +	}

again

> +	rcu_read_lock();
> +	entry = radix_tree_lookup(&mapping->page_tree, start & PMD_MASK);
> +	rcu_read_unlock();

What stabilizes the memory at *entry after rcu_read_unlock()?

> +	/* see if the start of our range is covered by a PMD entry */
> +	if (entry && RADIX_DAX_TYPE(entry) == RADIX_DAX_PMD)
> +		start &= PMD_MASK;
> +
> +	start_page = start >> PAGE_CACHE_SHIFT;
> +	end_page = end >> PAGE_CACHE_SHIFT;
> +
> +	tag_pages_for_writeback(mapping, start_page, end_page);
> +
> +	pagevec_init(&pvec, 0);
> +	while (1) {
> +		pvec.nr = find_get_entries_tag(mapping, start_page,
> +				PAGECACHE_TAG_TOWRITE, PAGEVEC_SIZE,
> +				pvec.pages, indices);
> +
> +		if (pvec.nr == 0)
> +			break;
> +
> +		for (i = 0; i < pvec.nr; i++)
> +			dax_writeback_one(mapping, indices[i], pvec.pages[i]);
> +	}
> +	wmb_pmem();
> +}
> +EXPORT_SYMBOL_GPL(dax_writeback_mapping_range);
> +
>
> ...
>

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Re: [PATCH v5 4/7] dax: add support for fsync/sync

[Andrew Morton]

On Fri, 18 Dec 2015 22:22:17 -0700 Ross Zwisler <ross.zwisler@linux.intel.com> wrote:

> To properly handle fsync/msync in an efficient way DAX needs to track dirty
> pages so it is able to flush them durably to media on demand.
> 
> The tracking of dirty pages is done via the radix tree in struct
> address_space.  This radix tree is already used by the page writeback
> infrastructure for tracking dirty pages associated with an open file, and
> it already has support for exceptional (non struct page*) entries.  We
> build upon these features to add exceptional entries to the radix tree for
> DAX dirty PMD or PTE pages at fault time.

I'm getting a few rejects here against other pending changes.  Things
look OK to me but please do runtime test the end result as it resides
in linux-next.  Which will be next year.

>
> ...
>
> +static void dax_writeback_one(struct address_space *mapping, pgoff_t index,
> +		void *entry)
> +{
> +	struct radix_tree_root *page_tree = &mapping->page_tree;
> +	int type = RADIX_DAX_TYPE(entry);
> +	struct radix_tree_node *node;
> +	void **slot;
> +
> +	if (type != RADIX_DAX_PTE && type != RADIX_DAX_PMD) {
> +		WARN_ON_ONCE(1);
> +		return;
> +	}

--- a/fs/dax.c~dax-add-support-for-fsync-sync-fix
+++ a/fs/dax.c
@@ -383,10 +383,8 @@ static void dax_writeback_one(struct add
 	struct radix_tree_node *node;
 	void **slot;
 
-	if (type != RADIX_DAX_PTE && type != RADIX_DAX_PMD) {
-		WARN_ON_ONCE(1);
+	if (WARN_ON_ONCE(type != RADIX_DAX_PTE && type != RADIX_DAX_PMD))
 		return;
-	}
 
 	spin_lock_irq(&mapping->tree_lock);
 	/*

> +	spin_lock_irq(&mapping->tree_lock);
> +	/*
> +	 * Regular page slots are stabilized by the page lock even
> +	 * without the tree itself locked.  These unlocked entries
> +	 * need verification under the tree lock.
> +	 */
> +	if (!__radix_tree_lookup(page_tree, index, &node, &slot))
> +		goto unlock;
> +	if (*slot != entry)
> +		goto unlock;
> +
> +	/* another fsync thread may have already written back this entry */
> +	if (!radix_tree_tag_get(page_tree, index, PAGECACHE_TAG_TOWRITE))
> +		goto unlock;
> +
> +	radix_tree_tag_clear(page_tree, index, PAGECACHE_TAG_TOWRITE);
> +
> +	if (type == RADIX_DAX_PMD)
> +		wb_cache_pmem(RADIX_DAX_ADDR(entry), PMD_SIZE);
> +	else
> +		wb_cache_pmem(RADIX_DAX_ADDR(entry), PAGE_SIZE);
> + unlock:
> +	spin_unlock_irq(&mapping->tree_lock);
> +}
> +
> +/*
> + * Flush the mapping to the persistent domain within the byte range of [start,
> + * end]. This is required by data integrity operations to ensure file data is
> + * on persistent storage prior to completion of the operation.
> + */
> +void dax_writeback_mapping_range(struct address_space *mapping, loff_t start,
> +		loff_t end)
> +{
> +	struct inode *inode = mapping->host;
> +	pgoff_t indices[PAGEVEC_SIZE];
> +	pgoff_t start_page, end_page;
> +	struct pagevec pvec;
> +	void *entry;
> +	int i;
> +
> +	if (inode->i_blkbits != PAGE_SHIFT) {
> +		WARN_ON_ONCE(1);
> +		return;
> +	}

again

> +	rcu_read_lock();
> +	entry = radix_tree_lookup(&mapping->page_tree, start & PMD_MASK);
> +	rcu_read_unlock();

What stabilizes the memory at *entry after rcu_read_unlock()?

> +	/* see if the start of our range is covered by a PMD entry */
> +	if (entry && RADIX_DAX_TYPE(entry) == RADIX_DAX_PMD)
> +		start &= PMD_MASK;
> +
> +	start_page = start >> PAGE_CACHE_SHIFT;
> +	end_page = end >> PAGE_CACHE_SHIFT;
> +
> +	tag_pages_for_writeback(mapping, start_page, end_page);
> +
> +	pagevec_init(&pvec, 0);
> +	while (1) {
> +		pvec.nr = find_get_entries_tag(mapping, start_page,
> +				PAGECACHE_TAG_TOWRITE, PAGEVEC_SIZE,
> +				pvec.pages, indices);
> +
> +		if (pvec.nr == 0)
> +			break;
> +
> +		for (i = 0; i < pvec.nr; i++)
> +			dax_writeback_one(mapping, indices[i], pvec.pages[i]);
> +	}
> +	wmb_pmem();
> +}
> +EXPORT_SYMBOL_GPL(dax_writeback_mapping_range);
> +
>
> ...
>

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Re: [PATCH v5 4/7] dax: add support for fsync/sync

[Ross Zwisler]

On Tue, Dec 22, 2015 at 02:46:25PM -0800, Andrew Morton wrote:
> On Fri, 18 Dec 2015 22:22:17 -0700 Ross Zwisler <ross.zwisler@linux.intel.com> wrote:
> 
> > To properly handle fsync/msync in an efficient way DAX needs to track dirty
> > pages so it is able to flush them durably to media on demand.
> > 
> > The tracking of dirty pages is done via the radix tree in struct
> > address_space.  This radix tree is already used by the page writeback
> > infrastructure for tracking dirty pages associated with an open file, and
> > it already has support for exceptional (non struct page*) entries.  We
> > build upon these features to add exceptional entries to the radix tree for
> > DAX dirty PMD or PTE pages at fault time.
> 
> I'm getting a few rejects here against other pending changes.  Things
> look OK to me but please do runtime test the end result as it resides
> in linux-next.  Which will be next year.

Sounds good.  I'm hoping to soon send out an updated version of this series
which merges with Dan's changes to dax.c.  Thank you for pulling these into
-mm.

> --- a/fs/dax.c~dax-add-support-for-fsync-sync-fix
> +++ a/fs/dax.c
> @@ -383,10 +383,8 @@ static void dax_writeback_one(struct add
>  	struct radix_tree_node *node;
>  	void **slot;
>  
> -	if (type != RADIX_DAX_PTE && type != RADIX_DAX_PMD) {
> -		WARN_ON_ONCE(1);
> +	if (WARN_ON_ONCE(type != RADIX_DAX_PTE && type != RADIX_DAX_PMD))
>  		return;
> -	}

This is much cleaner, thanks.  I'll make this change throughout my set.

> > +/*
> > + * Flush the mapping to the persistent domain within the byte range of [start,
> > + * end]. This is required by data integrity operations to ensure file data is
> > + * on persistent storage prior to completion of the operation.
> > + */
> > +void dax_writeback_mapping_range(struct address_space *mapping, loff_t start,
> > +		loff_t end)
> > +{
> > +	struct inode *inode = mapping->host;
> > +	pgoff_t indices[PAGEVEC_SIZE];
> > +	pgoff_t start_page, end_page;
> > +	struct pagevec pvec;
> > +	void *entry;
> > +	int i;
> > +
> > +	if (inode->i_blkbits != PAGE_SHIFT) {
> > +		WARN_ON_ONCE(1);
> > +		return;
> > +	}
> 
> again
> 
> > +	rcu_read_lock();
> > +	entry = radix_tree_lookup(&mapping->page_tree, start & PMD_MASK);
> > +	rcu_read_unlock();
> 
> What stabilizes the memory at *entry after rcu_read_unlock()?

Nothing in this function.  We use the entry that is currently in the tree to
know whether or not to expand the range of offsets that we need to flush.
Even if we are racing with someone, expanding our flushing range is
non-destructive.

We get a list of entries based on what is dirty later in this function via
find_get_entries_tag(), and before we take any action on those entries we
re-verify them while holding the tree_lock in dax_writeback_one().

The next version of this series will have updated version of this code which
also accounts for block device removal via dax_map_atomic() inside of
dax_writeback_one().

Re: [PATCH v5 4/7] dax: add support for fsync/sync

[Ross Zwisler]

On Tue, Dec 22, 2015 at 02:46:25PM -0800, Andrew Morton wrote:
> On Fri, 18 Dec 2015 22:22:17 -0700 Ross Zwisler <ross.zwisler@linux.intel.com> wrote:
> 
> > To properly handle fsync/msync in an efficient way DAX needs to track dirty
> > pages so it is able to flush them durably to media on demand.
> > 
> > The tracking of dirty pages is done via the radix tree in struct
> > address_space.  This radix tree is already used by the page writeback
> > infrastructure for tracking dirty pages associated with an open file, and
> > it already has support for exceptional (non struct page*) entries.  We
> > build upon these features to add exceptional entries to the radix tree for
> > DAX dirty PMD or PTE pages at fault time.
> 
> I'm getting a few rejects here against other pending changes.  Things
> look OK to me but please do runtime test the end result as it resides
> in linux-next.  Which will be next year.

Sounds good.  I'm hoping to soon send out an updated version of this series
which merges with Dan's changes to dax.c.  Thank you for pulling these into
-mm.

> --- a/fs/dax.c~dax-add-support-for-fsync-sync-fix
> +++ a/fs/dax.c
> @@ -383,10 +383,8 @@ static void dax_writeback_one(struct add
>  	struct radix_tree_node *node;
>  	void **slot;
>  
> -	if (type != RADIX_DAX_PTE && type != RADIX_DAX_PMD) {
> -		WARN_ON_ONCE(1);
> +	if (WARN_ON_ONCE(type != RADIX_DAX_PTE && type != RADIX_DAX_PMD))
>  		return;
> -	}

This is much cleaner, thanks.  I'll make this change throughout my set.

> > +/*
> > + * Flush the mapping to the persistent domain within the byte range of [start,
> > + * end]. This is required by data integrity operations to ensure file data is
> > + * on persistent storage prior to completion of the operation.
> > + */
> > +void dax_writeback_mapping_range(struct address_space *mapping, loff_t start,
> > +		loff_t end)
> > +{
> > +	struct inode *inode = mapping->host;
> > +	pgoff_t indices[PAGEVEC_SIZE];
> > +	pgoff_t start_page, end_page;
> > +	struct pagevec pvec;
> > +	void *entry;
> > +	int i;
> > +
> > +	if (inode->i_blkbits != PAGE_SHIFT) {
> > +		WARN_ON_ONCE(1);
> > +		return;
> > +	}
> 
> again
> 
> > +	rcu_read_lock();
> > +	entry = radix_tree_lookup(&mapping->page_tree, start & PMD_MASK);
> > +	rcu_read_unlock();
> 
> What stabilizes the memory at *entry after rcu_read_unlock()?

Nothing in this function.  We use the entry that is currently in the tree to
know whether or not to expand the range of offsets that we need to flush.
Even if we are racing with someone, expanding our flushing range is
non-destructive.

We get a list of entries based on what is dirty later in this function via
find_get_entries_tag(), and before we take any action on those entries we
re-verify them while holding the tree_lock in dax_writeback_one().

The next version of this series will have updated version of this code which
also accounts for block device removal via dax_map_atomic() inside of
dax_writeback_one().

--
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Re: [PATCH v5 4/7] dax: add support for fsync/sync

[Ross Zwisler]

On Tue, Dec 22, 2015 at 02:46:25PM -0800, Andrew Morton wrote:
> On Fri, 18 Dec 2015 22:22:17 -0700 Ross Zwisler <ross.zwisler@linux.intel.com> wrote:
> 
> > To properly handle fsync/msync in an efficient way DAX needs to track dirty
> > pages so it is able to flush them durably to media on demand.
> > 
> > The tracking of dirty pages is done via the radix tree in struct
> > address_space.  This radix tree is already used by the page writeback
> > infrastructure for tracking dirty pages associated with an open file, and
> > it already has support for exceptional (non struct page*) entries.  We
> > build upon these features to add exceptional entries to the radix tree for
> > DAX dirty PMD or PTE pages at fault time.
> 
> I'm getting a few rejects here against other pending changes.  Things
> look OK to me but please do runtime test the end result as it resides
> in linux-next.  Which will be next year.

Sounds good.  I'm hoping to soon send out an updated version of this series
which merges with Dan's changes to dax.c.  Thank you for pulling these into
-mm.

> --- a/fs/dax.c~dax-add-support-for-fsync-sync-fix
> +++ a/fs/dax.c
> @@ -383,10 +383,8 @@ static void dax_writeback_one(struct add
>  	struct radix_tree_node *node;
>  	void **slot;
>  
> -	if (type != RADIX_DAX_PTE && type != RADIX_DAX_PMD) {
> -		WARN_ON_ONCE(1);
> +	if (WARN_ON_ONCE(type != RADIX_DAX_PTE && type != RADIX_DAX_PMD))
>  		return;
> -	}

This is much cleaner, thanks.  I'll make this change throughout my set.

> > +/*
> > + * Flush the mapping to the persistent domain within the byte range of [start,
> > + * end]. This is required by data integrity operations to ensure file data is
> > + * on persistent storage prior to completion of the operation.
> > + */
> > +void dax_writeback_mapping_range(struct address_space *mapping, loff_t start,
> > +		loff_t end)
> > +{
> > +	struct inode *inode = mapping->host;
> > +	pgoff_t indices[PAGEVEC_SIZE];
> > +	pgoff_t start_page, end_page;
> > +	struct pagevec pvec;
> > +	void *entry;
> > +	int i;
> > +
> > +	if (inode->i_blkbits != PAGE_SHIFT) {
> > +		WARN_ON_ONCE(1);
> > +		return;
> > +	}
> 
> again
> 
> > +	rcu_read_lock();
> > +	entry = radix_tree_lookup(&mapping->page_tree, start & PMD_MASK);
> > +	rcu_read_unlock();
> 
> What stabilizes the memory at *entry after rcu_read_unlock()?

Nothing in this function.  We use the entry that is currently in the tree to
know whether or not to expand the range of offsets that we need to flush.
Even if we are racing with someone, expanding our flushing range is
non-destructive.

We get a list of entries based on what is dirty later in this function via
find_get_entries_tag(), and before we take any action on those entries we
re-verify them while holding the tree_lock in dax_writeback_one().

The next version of this series will have updated version of this code which
also accounts for block device removal via dax_map_atomic() inside of
dax_writeback_one().

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Re: [PATCH v5 1/7] pmem: add wb_cache_pmem() to the PMEM API

[Ross Zwisler]

On Tue, Dec 22, 2015 at 02:44:40PM -0800, Andrew Morton wrote:
> On Fri, 18 Dec 2015 22:22:14 -0700 Ross Zwisler <ross.zwisler@linux.intel.com> wrote:
> 
> > The function __arch_wb_cache_pmem() was already an internal implementation
> > detail of the x86 PMEM API, but this functionality needs to be exported as
> > part of the general PMEM API to handle the fsync/msync case for DAX mmaps.
> > 
> > One thing worth noting is that we really do want this to be part of the
> > PMEM API as opposed to a stand-alone function like clflush_cache_range()
> > because of ordering restrictions.  By having wb_cache_pmem() as part of the
> > PMEM API we can leave it unordered, call it multiple times to write back
> > large amounts of memory, and then order the multiple calls with a single
> > wmb_pmem().
> > 
> > @@ -138,7 +139,7 @@ static inline void arch_clear_pmem(void __pmem *addr, size_t size)
> >  	else
> >  		memset(vaddr, 0, size);
> >  
> > -	__arch_wb_cache_pmem(vaddr, size);
> > +	arch_wb_cache_pmem(addr, size);
> >  }
> >  
> 
> reject.  I made this
> 
> 	arch_wb_cache_pmem(vaddr, size);
> 
> due to Dan's
> http://www.ozlabs.org/~akpm/mmots/broken-out/pmem-dax-clean-up-clear_pmem.patch

The first argument seems wrong to me - in arch_clear_pmem() 'addr' and 'vaddr'
are the same address, with the only difference being 'addr' has the __pmem
annotation.

As of this patch arch_wb_cache_pmem() follows the lead of the rest of the
exported PMEM API functions and takes an argument that has the __pmem
annotation, so I believe it should be:

arch_wb_cache_pmem(addr, size);

Without this I think you'll get a sparse warning.

This will be fixed up in the next version of my series which build upon Dan's
patches.

Re: [PATCH v5 1/7] pmem: add wb_cache_pmem() to the PMEM API

[Ross Zwisler]

On Tue, Dec 22, 2015 at 02:44:40PM -0800, Andrew Morton wrote:
> On Fri, 18 Dec 2015 22:22:14 -0700 Ross Zwisler <ross.zwisler@linux.intel.com> wrote:
> 
> > The function __arch_wb_cache_pmem() was already an internal implementation
> > detail of the x86 PMEM API, but this functionality needs to be exported as
> > part of the general PMEM API to handle the fsync/msync case for DAX mmaps.
> > 
> > One thing worth noting is that we really do want this to be part of the
> > PMEM API as opposed to a stand-alone function like clflush_cache_range()
> > because of ordering restrictions.  By having wb_cache_pmem() as part of the
> > PMEM API we can leave it unordered, call it multiple times to write back
> > large amounts of memory, and then order the multiple calls with a single
> > wmb_pmem().
> > 
> > @@ -138,7 +139,7 @@ static inline void arch_clear_pmem(void __pmem *addr, size_t size)
> >  	else
> >  		memset(vaddr, 0, size);
> >  
> > -	__arch_wb_cache_pmem(vaddr, size);
> > +	arch_wb_cache_pmem(addr, size);
> >  }
> >  
> 
> reject.  I made this
> 
> 	arch_wb_cache_pmem(vaddr, size);
> 
> due to Dan's
> http://www.ozlabs.org/~akpm/mmots/broken-out/pmem-dax-clean-up-clear_pmem.patch

The first argument seems wrong to me - in arch_clear_pmem() 'addr' and 'vaddr'
are the same address, with the only difference being 'addr' has the __pmem
annotation.

As of this patch arch_wb_cache_pmem() follows the lead of the rest of the
exported PMEM API functions and takes an argument that has the __pmem
annotation, so I believe it should be:

arch_wb_cache_pmem(addr, size);

Without this I think you'll get a sparse warning.

This will be fixed up in the next version of my series which build upon Dan's
patches.

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Re: [PATCH v5 1/7] pmem: add wb_cache_pmem() to the PMEM API

[Ross Zwisler]

On Tue, Dec 22, 2015 at 02:44:40PM -0800, Andrew Morton wrote:
> On Fri, 18 Dec 2015 22:22:14 -0700 Ross Zwisler <ross.zwisler@linux.intel.com> wrote:
> 
> > The function __arch_wb_cache_pmem() was already an internal implementation
> > detail of the x86 PMEM API, but this functionality needs to be exported as
> > part of the general PMEM API to handle the fsync/msync case for DAX mmaps.
> > 
> > One thing worth noting is that we really do want this to be part of the
> > PMEM API as opposed to a stand-alone function like clflush_cache_range()
> > because of ordering restrictions.  By having wb_cache_pmem() as part of the
> > PMEM API we can leave it unordered, call it multiple times to write back
> > large amounts of memory, and then order the multiple calls with a single
> > wmb_pmem().
> > 
> > @@ -138,7 +139,7 @@ static inline void arch_clear_pmem(void __pmem *addr, size_t size)
> >  	else
> >  		memset(vaddr, 0, size);
> >  
> > -	__arch_wb_cache_pmem(vaddr, size);
> > +	arch_wb_cache_pmem(addr, size);
> >  }
> >  
> 
> reject.  I made this
> 
> 	arch_wb_cache_pmem(vaddr, size);
> 
> due to Dan's
> http://www.ozlabs.org/~akpm/mmots/broken-out/pmem-dax-clean-up-clear_pmem.patch

The first argument seems wrong to me - in arch_clear_pmem() 'addr' and 'vaddr'
are the same address, with the only difference being 'addr' has the __pmem
annotation.

As of this patch arch_wb_cache_pmem() follows the lead of the rest of the
exported PMEM API functions and takes an argument that has the __pmem
annotation, so I believe it should be:

arch_wb_cache_pmem(addr, size);

Without this I think you'll get a sparse warning.

This will be fixed up in the next version of my series which build upon Dan's
patches.

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Re: [PATCH v5 2/7] dax: support dirty DAX entries in radix tree

[Ross Zwisler]

On Tue, Dec 22, 2015 at 02:46:05PM -0800, Andrew Morton wrote:
> On Fri, 18 Dec 2015 22:22:15 -0700 Ross Zwisler <ross.zwisler@linux.intel.com> wrote:
> 
> > Add support for tracking dirty DAX entries in the struct address_space
> > radix tree.  This tree is already used for dirty page writeback, and it
> > already supports the use of exceptional (non struct page*) entries.
> > 
> > In order to properly track dirty DAX pages we will insert new exceptional
> > entries into the radix tree that represent dirty DAX PTE or PMD pages.
> > These exceptional entries will also contain the writeback addresses for the
> > PTE or PMD faults that we can use at fsync/msync time.
> > 
> > There are currently two types of exceptional entries (shmem and shadow)
> > that can be placed into the radix tree, and this adds a third.  We rely on
> > the fact that only one type of exceptional entry can be found in a given
> > radix tree based on its usage.  This happens for free with DAX vs shmem but
> > we explicitly prevent shadow entries from being added to radix trees for
> > DAX mappings.
> > 
> > The only shadow entries that would be generated for DAX radix trees would
> > be to track zero page mappings that were created for holes.  These pages
> > would receive minimal benefit from having shadow entries, and the choice
> > to have only one type of exceptional entry in a given radix tree makes the
> > logic simpler both in clear_exceptional_entry() and in the rest of DAX.
> > 
> >
> > ...
> >
> > --- a/include/linux/dax.h
> > +++ b/include/linux/dax.h
> > @@ -36,4 +36,9 @@ static inline bool vma_is_dax(struct vm_area_struct *vma)
> >  {
> >  	return vma->vm_file && IS_DAX(vma->vm_file->f_mapping->host);
> >  }
> > +
> > +static inline bool dax_mapping(struct address_space *mapping)
> > +{
> > +	return mapping->host && IS_DAX(mapping->host);
> > +}
> 
> Can we make this evaluate to plain old "0" when CONFIG_FS_DAX=n?  That
> way a bunch of code in callers will fall away as well.
> 
> If the compiler has any brains then a good way to do this would be to
> make IS_DAX be "0" but one would need to check that the zeroness
> properly propagated out of the inline.

Ah, it already works that way due to some magic with IS_DAX().  I believe we
already use the fact that blocks protected by IS_DAX() go away if
CONFIG_FS_DAX isn't set.

The trick is that S_DAX is defined to be 0 if CONFIG_FS_DAX isn't set.

I'm pretty sure this is working because of the code in
filemap_write_and_wait_range().  I added a block with the later "dax: add
support for fsync/msync" patch which looks like this:

@@ -482,6 +482,9 @@ int filemap_write_and_wait_range(struct address_space *mapping,
 {
        int err = 0;
 
+       if (dax_mapping(mapping) && mapping->nrdax)
+               dax_writeback_mapping_range(mapping, lstart, lend);
+

Without the dax_mapping() check there the behavior is the same, but we fail to
compile if CONFIG_FS_DAX isn't set because dax_writeback_mapping_range() isn't
defined.  (Guess how I found that out.  :)  )

> >  #endif
> > diff --git a/include/linux/fs.h b/include/linux/fs.h
> > index 3aa5142..b9ac534 100644
> > --- a/include/linux/fs.h
> > +++ b/include/linux/fs.h
> > @@ -433,6 +433,7 @@ struct address_space {
> >  	/* Protected by tree_lock together with the radix tree */
> >  	unsigned long		nrpages;	/* number of total pages */
> >  	unsigned long		nrshadows;	/* number of shadow entries */
> > +	unsigned long		nrdax;	        /* number of DAX entries */
> 
> hm, that's unfortunate - machines commonly carry tremendous numbers of
> address_spaces in memory and adding pork to them is rather a big deal. 
> We can't avoid this somehow?  Maybe share the space with nrshadows by
> some means?  Find some other field which is unused for dax files?

Jan Kara noticed the same thing:

https://lists.01.org/pipermail/linux-nvdimm/2015-December/003626.html

It'll be fixed in the next spin of the patch set.

Re: [PATCH v5 2/7] dax: support dirty DAX entries in radix tree

[Ross Zwisler]

On Tue, Dec 22, 2015 at 02:46:05PM -0800, Andrew Morton wrote:
> On Fri, 18 Dec 2015 22:22:15 -0700 Ross Zwisler <ross.zwisler@linux.intel.com> wrote:
> 
> > Add support for tracking dirty DAX entries in the struct address_space
> > radix tree.  This tree is already used for dirty page writeback, and it
> > already supports the use of exceptional (non struct page*) entries.
> > 
> > In order to properly track dirty DAX pages we will insert new exceptional
> > entries into the radix tree that represent dirty DAX PTE or PMD pages.
> > These exceptional entries will also contain the writeback addresses for the
> > PTE or PMD faults that we can use at fsync/msync time.
> > 
> > There are currently two types of exceptional entries (shmem and shadow)
> > that can be placed into the radix tree, and this adds a third.  We rely on
> > the fact that only one type of exceptional entry can be found in a given
> > radix tree based on its usage.  This happens for free with DAX vs shmem but
> > we explicitly prevent shadow entries from being added to radix trees for
> > DAX mappings.
> > 
> > The only shadow entries that would be generated for DAX radix trees would
> > be to track zero page mappings that were created for holes.  These pages
> > would receive minimal benefit from having shadow entries, and the choice
> > to have only one type of exceptional entry in a given radix tree makes the
> > logic simpler both in clear_exceptional_entry() and in the rest of DAX.
> > 
> >
> > ...
> >
> > --- a/include/linux/dax.h
> > +++ b/include/linux/dax.h
> > @@ -36,4 +36,9 @@ static inline bool vma_is_dax(struct vm_area_struct *vma)
> >  {
> >  	return vma->vm_file && IS_DAX(vma->vm_file->f_mapping->host);
> >  }
> > +
> > +static inline bool dax_mapping(struct address_space *mapping)
> > +{
> > +	return mapping->host && IS_DAX(mapping->host);
> > +}
> 
> Can we make this evaluate to plain old "0" when CONFIG_FS_DAX=n?  That
> way a bunch of code in callers will fall away as well.
> 
> If the compiler has any brains then a good way to do this would be to
> make IS_DAX be "0" but one would need to check that the zeroness
> properly propagated out of the inline.

Ah, it already works that way due to some magic with IS_DAX().  I believe we
already use the fact that blocks protected by IS_DAX() go away if
CONFIG_FS_DAX isn't set.

The trick is that S_DAX is defined to be 0 if CONFIG_FS_DAX isn't set.

I'm pretty sure this is working because of the code in
filemap_write_and_wait_range().  I added a block with the later "dax: add
support for fsync/msync" patch which looks like this:

@@ -482,6 +482,9 @@ int filemap_write_and_wait_range(struct address_space *mapping,
 {
        int err = 0;
 
+       if (dax_mapping(mapping) && mapping->nrdax)
+               dax_writeback_mapping_range(mapping, lstart, lend);
+

Without the dax_mapping() check there the behavior is the same, but we fail to
compile if CONFIG_FS_DAX isn't set because dax_writeback_mapping_range() isn't
defined.  (Guess how I found that out.  :)  )

> >  #endif
> > diff --git a/include/linux/fs.h b/include/linux/fs.h
> > index 3aa5142..b9ac534 100644
> > --- a/include/linux/fs.h
> > +++ b/include/linux/fs.h
> > @@ -433,6 +433,7 @@ struct address_space {
> >  	/* Protected by tree_lock together with the radix tree */
> >  	unsigned long		nrpages;	/* number of total pages */
> >  	unsigned long		nrshadows;	/* number of shadow entries */
> > +	unsigned long		nrdax;	        /* number of DAX entries */
> 
> hm, that's unfortunate - machines commonly carry tremendous numbers of
> address_spaces in memory and adding pork to them is rather a big deal. 
> We can't avoid this somehow?  Maybe share the space with nrshadows by
> some means?  Find some other field which is unused for dax files?

Jan Kara noticed the same thing:

https://lists.01.org/pipermail/linux-nvdimm/2015-December/003626.html

It'll be fixed in the next spin of the patch set.

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
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Re: [PATCH v5 2/7] dax: support dirty DAX entries in radix tree

[Ross Zwisler]

On Tue, Dec 22, 2015 at 02:46:05PM -0800, Andrew Morton wrote:
> On Fri, 18 Dec 2015 22:22:15 -0700 Ross Zwisler <ross.zwisler@linux.intel.com> wrote:
> 
> > Add support for tracking dirty DAX entries in the struct address_space
> > radix tree.  This tree is already used for dirty page writeback, and it
> > already supports the use of exceptional (non struct page*) entries.
> > 
> > In order to properly track dirty DAX pages we will insert new exceptional
> > entries into the radix tree that represent dirty DAX PTE or PMD pages.
> > These exceptional entries will also contain the writeback addresses for the
> > PTE or PMD faults that we can use at fsync/msync time.
> > 
> > There are currently two types of exceptional entries (shmem and shadow)
> > that can be placed into the radix tree, and this adds a third.  We rely on
> > the fact that only one type of exceptional entry can be found in a given
> > radix tree based on its usage.  This happens for free with DAX vs shmem but
> > we explicitly prevent shadow entries from being added to radix trees for
> > DAX mappings.
> > 
> > The only shadow entries that would be generated for DAX radix trees would
> > be to track zero page mappings that were created for holes.  These pages
> > would receive minimal benefit from having shadow entries, and the choice
> > to have only one type of exceptional entry in a given radix tree makes the
> > logic simpler both in clear_exceptional_entry() and in the rest of DAX.
> > 
> >
> > ...
> >
> > --- a/include/linux/dax.h
> > +++ b/include/linux/dax.h
> > @@ -36,4 +36,9 @@ static inline bool vma_is_dax(struct vm_area_struct *vma)
> >  {
> >  	return vma->vm_file && IS_DAX(vma->vm_file->f_mapping->host);
> >  }
> > +
> > +static inline bool dax_mapping(struct address_space *mapping)
> > +{
> > +	return mapping->host && IS_DAX(mapping->host);
> > +}
> 
> Can we make this evaluate to plain old "0" when CONFIG_FS_DAX=n?  That
> way a bunch of code in callers will fall away as well.
> 
> If the compiler has any brains then a good way to do this would be to
> make IS_DAX be "0" but one would need to check that the zeroness
> properly propagated out of the inline.

Ah, it already works that way due to some magic with IS_DAX().  I believe we
already use the fact that blocks protected by IS_DAX() go away if
CONFIG_FS_DAX isn't set.

The trick is that S_DAX is defined to be 0 if CONFIG_FS_DAX isn't set.

I'm pretty sure this is working because of the code in
filemap_write_and_wait_range().  I added a block with the later "dax: add
support for fsync/msync" patch which looks like this:

@@ -482,6 +482,9 @@ int filemap_write_and_wait_range(struct address_space *mapping,
 {
        int err = 0;
 
+       if (dax_mapping(mapping) && mapping->nrdax)
+               dax_writeback_mapping_range(mapping, lstart, lend);
+

Without the dax_mapping() check there the behavior is the same, but we fail to
compile if CONFIG_FS_DAX isn't set because dax_writeback_mapping_range() isn't
defined.  (Guess how I found that out.  :)  )

> >  #endif
> > diff --git a/include/linux/fs.h b/include/linux/fs.h
> > index 3aa5142..b9ac534 100644
> > --- a/include/linux/fs.h
> > +++ b/include/linux/fs.h
> > @@ -433,6 +433,7 @@ struct address_space {
> >  	/* Protected by tree_lock together with the radix tree */
> >  	unsigned long		nrpages;	/* number of total pages */
> >  	unsigned long		nrshadows;	/* number of shadow entries */
> > +	unsigned long		nrdax;	        /* number of DAX entries */
> 
> hm, that's unfortunate - machines commonly carry tremendous numbers of
> address_spaces in memory and adding pork to them is rather a big deal. 
> We can't avoid this somehow?  Maybe share the space with nrshadows by
> some means?  Find some other field which is unused for dax files?

Jan Kara noticed the same thing:

https://lists.01.org/pipermail/linux-nvdimm/2015-December/003626.html

It'll be fixed in the next spin of the patch set.

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http://oss.sgi.com/mailman/listinfo/xfs