[PATCH v4 00/12] Change readahead API

[PATCH v4 00/12] Change readahead API

[Matthew Wilcox]

From: "Matthew Wilcox (Oracle)" <willy@infradead.org>

I would particularly value feedback on this from the gfs2 and ocfs2
maintainers.  They have non-trivial changes, and a review on patch 5
would be greatly appreciated.

This series adds a readahead address_space operation to eventually
replace the readpages operation.  The key difference is that
pages are added to the page cache as they are allocated (and
then looked up by the filesystem) instead of passing them on a
list to the readpages operation and having the filesystem add
them to the page cache.  It's a net reduction in code for each
implementation, more efficient than walking a list, and solves
the direct-write vs buffered-read problem reported by yu kuai at
https://lore.kernel.org/linux-fsdevel/20200116063601.39201-1-yukuai3@huawei.com/

v4:
 - Rebase on current Linus (a62aa6f7f50a ("Merge tag 'gfs2-for-5.6'"))
 - Add comment to __do_page_cache_readahead() acknowledging we don't
   care _that_ much about setting PageReadahead.
 - Fix the return value check of add_to_page_cache_lru().
 - Add a missing call to put_page() in __do_page_cache_readahead() if
   we fail to insert the page.
 - Improve the documentation of ->readahead (including indentation
   problem identified by Randy).
 - Fix off by one error in read_pages() (Dave Chinner).
 - Fix nr_pages manipulation in btrfs (Dave Chinner).
 - Remove bogus refcount fix in erofs (Gao Xiang, Dave Chinner).
 - Update ext4 patch for Merkle tree readahead.
 - Update f2fs patch for Merkle tree readahead.
 - Reinstate next_page label in f2fs_readpages() now it's used by the
   compression code.
 - Reinstate call to fuse_wait_on_page_writeback (Miklos Szeredi).
 - Remove a double-unlock in the error path in fuse.
 - Remove an odd fly-speck in fuse_readpages().
 - Make nr_pages loop in fuse_readpages less convoluted (Dave Chinner).

Matthew Wilcox (Oracle) (12):
  mm: Fix the return type of __do_page_cache_readahead
  readahead: Ignore return value of ->readpages
  readahead: Put pages in cache earlier
  mm: Add readahead address space operation
  fs: Convert mpage_readpages to mpage_readahead
  btrfs: Convert from readpages to readahead
  erofs: Convert uncompressed files from readpages to readahead
  erofs: Convert compressed files from readpages to readahead
  ext4: Convert from readpages to readahead
  f2fs: Convert from readpages to readahead
  fuse: Convert from readpages to readahead
  iomap: Convert from readpages to readahead

 Documentation/filesystems/locking.rst |  7 ++-
 Documentation/filesystems/vfs.rst     | 14 +++++
 drivers/staging/exfat/exfat_super.c   |  9 +--
 fs/block_dev.c                        |  9 +--
 fs/btrfs/extent_io.c                  | 19 +++---
 fs/btrfs/extent_io.h                  |  2 +-
 fs/btrfs/inode.c                      | 18 +++---
 fs/erofs/data.c                       | 33 ++++------
 fs/erofs/zdata.c                      | 21 +++----
 fs/ext2/inode.c                       | 12 ++--
 fs/ext4/ext4.h                        |  5 +-
 fs/ext4/inode.c                       | 24 ++++----
 fs/ext4/readpage.c                    | 20 +++---
 fs/ext4/verity.c                      | 16 +++--
 fs/f2fs/data.c                        | 35 +++++------
 fs/f2fs/f2fs.h                        |  5 +-
 fs/f2fs/verity.c                      | 16 +++--
 fs/fat/inode.c                        |  8 +--
 fs/fuse/file.c                        | 37 +++++------
 fs/gfs2/aops.c                        | 20 +++---
 fs/hpfs/file.c                        |  8 +--
 fs/iomap/buffered-io.c                | 74 +++++-----------------
 fs/iomap/trace.h                      |  2 +-
 fs/isofs/inode.c                      |  9 +--
 fs/jfs/inode.c                        |  8 +--
 fs/mpage.c                            | 38 ++++--------
 fs/nilfs2/inode.c                     | 13 ++--
 fs/ocfs2/aops.c                       | 32 +++++-----
 fs/omfs/file.c                        |  8 +--
 fs/qnx6/inode.c                       |  8 +--
 fs/reiserfs/inode.c                   | 10 +--
 fs/udf/inode.c                        |  8 +--
 fs/xfs/xfs_aops.c                     | 10 +--
 include/linux/fs.h                    |  2 +
 include/linux/iomap.h                 |  2 +-
 include/linux/mpage.h                 |  2 +-
 include/linux/pagemap.h               | 12 ++++
 include/trace/events/erofs.h          |  6 +-
 include/trace/events/f2fs.h           |  6 +-
 mm/internal.h                         |  2 +-
 mm/migrate.c                          |  2 +-
 mm/readahead.c                        | 89 ++++++++++++++++++---------
 42 files changed, 332 insertions(+), 349 deletions(-)

-- 
2.24.1

[PATCH v4 01/12] mm: Fix the return type of __do_page_cache_readahead

[Matthew Wilcox]

From: "Matthew Wilcox (Oracle)" <willy@infradead.org>

ra_submit() which is a wrapper around __do_page_cache_readahead() already
returns an unsigned long, and the 'nr_to_read' parameter is an unsigned
long, so fix __do_page_cache_readahead() to return an unsigned long,
even though I'm pretty sure we're not going to readahead more than 2^32
pages ever.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 mm/internal.h  | 2 +-
 mm/readahead.c | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/mm/internal.h b/mm/internal.h
index 3cf20ab3ca01..41b93c4b3ab7 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -49,7 +49,7 @@ void unmap_page_range(struct mmu_gather *tlb,
 			     unsigned long addr, unsigned long end,
 			     struct zap_details *details);
 
-extern unsigned int __do_page_cache_readahead(struct address_space *mapping,
+extern unsigned long __do_page_cache_readahead(struct address_space *mapping,
 		struct file *filp, pgoff_t offset, unsigned long nr_to_read,
 		unsigned long lookahead_size);
 
diff --git a/mm/readahead.c b/mm/readahead.c
index 2fe72cd29b47..6bf73ef33b7e 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -152,7 +152,7 @@ static int read_pages(struct address_space *mapping, struct file *filp,
  *
  * Returns the number of pages requested, or the maximum amount of I/O allowed.
  */
-unsigned int __do_page_cache_readahead(struct address_space *mapping,
+unsigned long __do_page_cache_readahead(struct address_space *mapping,
 		struct file *filp, pgoff_t offset, unsigned long nr_to_read,
 		unsigned long lookahead_size)
 {
@@ -161,7 +161,7 @@ unsigned int __do_page_cache_readahead(struct address_space *mapping,
 	unsigned long end_index;	/* The last page we want to read */
 	LIST_HEAD(page_pool);
 	int page_idx;
-	unsigned int nr_pages = 0;
+	unsigned long nr_pages = 0;
 	loff_t isize = i_size_read(inode);
 	gfp_t gfp_mask = readahead_gfp_mask(mapping);
 
-- 
2.24.1

[PATCH v4 02/12] readahead: Ignore return value of ->readpages

[Matthew Wilcox]

From: "Matthew Wilcox (Oracle)" <willy@infradead.org>

We used to assign the return value to a variable, which we then ignored.
Remove the pretence of caring.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 mm/readahead.c | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/mm/readahead.c b/mm/readahead.c
index 6bf73ef33b7e..fc77d13af556 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -113,17 +113,16 @@ int read_cache_pages(struct address_space *mapping, struct list_head *pages,
 
 EXPORT_SYMBOL(read_cache_pages);
 
-static int read_pages(struct address_space *mapping, struct file *filp,
+static void read_pages(struct address_space *mapping, struct file *filp,
 		struct list_head *pages, unsigned int nr_pages, gfp_t gfp)
 {
 	struct blk_plug plug;
 	unsigned page_idx;
-	int ret;
 
 	blk_start_plug(&plug);
 
 	if (mapping->a_ops->readpages) {
-		ret = mapping->a_ops->readpages(filp, mapping, pages, nr_pages);
+		mapping->a_ops->readpages(filp, mapping, pages, nr_pages);
 		/* Clean up the remaining pages */
 		put_pages_list(pages);
 		goto out;
@@ -136,12 +135,9 @@ static int read_pages(struct address_space *mapping, struct file *filp,
 			mapping->a_ops->readpage(filp, page);
 		put_page(page);
 	}
-	ret = 0;
 
 out:
 	blk_finish_plug(&plug);
-
-	return ret;
 }
 
 /*
-- 
2.24.1

[PATCH v4 03/12] readahead: Put pages in cache earlier

[Matthew Wilcox]

From: "Matthew Wilcox (Oracle)" <willy@infradead.org>

At allocation time, put the pages in the cache unless we're using
->readpages.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: linux-btrfs@vger.kernel.org
Cc: linux-erofs@lists.ozlabs.org
Cc: linux-ext4@vger.kernel.org
Cc: linux-f2fs-devel@lists.sourceforge.net
Cc: linux-xfs@vger.kernel.org
Cc: cluster-devel@redhat.com
Cc: ocfs2-devel@oss.oracle.com
---
 mm/readahead.c | 64 ++++++++++++++++++++++++++++++++++----------------
 1 file changed, 44 insertions(+), 20 deletions(-)

diff --git a/mm/readahead.c b/mm/readahead.c
index fc77d13af556..7daef0038b14 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -114,10 +114,10 @@ int read_cache_pages(struct address_space *mapping, struct list_head *pages,
 EXPORT_SYMBOL(read_cache_pages);
 
 static void read_pages(struct address_space *mapping, struct file *filp,
-		struct list_head *pages, unsigned int nr_pages, gfp_t gfp)
+		struct list_head *pages, pgoff_t start,
+		unsigned int nr_pages)
 {
 	struct blk_plug plug;
-	unsigned page_idx;
 
 	blk_start_plug(&plug);
 
@@ -125,18 +125,17 @@ static void read_pages(struct address_space *mapping, struct file *filp,
 		mapping->a_ops->readpages(filp, mapping, pages, nr_pages);
 		/* Clean up the remaining pages */
 		put_pages_list(pages);
-		goto out;
-	}
+	} else {
+		struct page *page;
+		unsigned long index;
 
-	for (page_idx = 0; page_idx < nr_pages; page_idx++) {
-		struct page *page = lru_to_page(pages);
-		list_del(&page->lru);
-		if (!add_to_page_cache_lru(page, mapping, page->index, gfp))
+		xa_for_each_range(&mapping->i_pages, index, page, start,
+				start + nr_pages - 1) {
 			mapping->a_ops->readpage(filp, page);
-		put_page(page);
+			put_page(page);
+		}
 	}
 
-out:
 	blk_finish_plug(&plug);
 }
 
@@ -153,13 +152,14 @@ unsigned long __do_page_cache_readahead(struct address_space *mapping,
 		unsigned long lookahead_size)
 {
 	struct inode *inode = mapping->host;
-	struct page *page;
 	unsigned long end_index;	/* The last page we want to read */
 	LIST_HEAD(page_pool);
 	int page_idx;
+	pgoff_t page_offset;
 	unsigned long nr_pages = 0;
 	loff_t isize = i_size_read(inode);
 	gfp_t gfp_mask = readahead_gfp_mask(mapping);
+	bool use_list = mapping->a_ops->readpages;
 
 	if (isize == 0)
 		goto out;
@@ -170,21 +170,32 @@ unsigned long __do_page_cache_readahead(struct address_space *mapping,
 	 * Preallocate as many pages as we will need.
 	 */
 	for (page_idx = 0; page_idx < nr_to_read; page_idx++) {
-		pgoff_t page_offset = offset + page_idx;
+		struct page *page;
 
+		page_offset = offset + page_idx;
 		if (page_offset > end_index)
 			break;
 
 		page = xa_load(&mapping->i_pages, page_offset);
 		if (page && !xa_is_value(page)) {
 			/*
-			 * Page already present?  Kick off the current batch of
-			 * contiguous pages before continuing with the next
-			 * batch.
+			 * Page already present?  Kick off the current batch
+			 * of contiguous pages before continuing with the
+			 * next batch.
 			 */
 			if (nr_pages)
-				read_pages(mapping, filp, &page_pool, nr_pages,
-						gfp_mask);
+				read_pages(mapping, filp, &page_pool,
+						page_offset - nr_pages,
+						nr_pages);
+			/*
+			 * It's possible this page is the page we should
+			 * be marking with PageReadahead.  However, we
+			 * don't have a stable ref to this page so it might
+			 * be reallocated to another user before we can set
+			 * the bit.  There's probably another page in the
+			 * cache marked with PageReadahead from the other
+			 * process which accessed this file.
+			 */
 			nr_pages = 0;
 			continue;
 		}
@@ -192,8 +203,20 @@ unsigned long __do_page_cache_readahead(struct address_space *mapping,
 		page = __page_cache_alloc(gfp_mask);
 		if (!page)
 			break;
-		page->index = page_offset;
-		list_add(&page->lru, &page_pool);
+		if (use_list) {
+			page->index = page_offset;
+			list_add(&page->lru, &page_pool);
+		} else if (add_to_page_cache_lru(page, mapping, page_offset,
+					gfp_mask) < 0) {
+			if (nr_pages)
+				read_pages(mapping, filp, &page_pool,
+						page_offset - nr_pages,
+						nr_pages);
+			put_page(page);
+			nr_pages = 0;
+			continue;
+		}
+
 		if (page_idx == nr_to_read - lookahead_size)
 			SetPageReadahead(page);
 		nr_pages++;
@@ -205,7 +228,8 @@ unsigned long __do_page_cache_readahead(struct address_space *mapping,
 	 * will then handle the error.
 	 */
 	if (nr_pages)
-		read_pages(mapping, filp, &page_pool, nr_pages, gfp_mask);
+		read_pages(mapping, filp, &page_pool, page_offset - nr_pages,
+				nr_pages);
 	BUG_ON(!list_empty(&page_pool));
 out:
 	return nr_pages;
-- 
2.24.1

[PATCH v4 04/12] mm: Add readahead address space operation

[Matthew Wilcox]

From: "Matthew Wilcox (Oracle)" <willy@infradead.org>

This replaces ->readpages with a saner interface:
 - Return the number of pages not read instead of an ignored error code.
 - Pages are already in the page cache when ->readahead is called.
 - Implementation looks up the pages in the page cache instead of
   having them passed in a linked list.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: linux-btrfs@vger.kernel.org
Cc: linux-erofs@lists.ozlabs.org
Cc: linux-ext4@vger.kernel.org
Cc: linux-f2fs-devel@lists.sourceforge.net
Cc: linux-xfs@vger.kernel.org
Cc: cluster-devel@redhat.com
Cc: ocfs2-devel@oss.oracle.com
---
 Documentation/filesystems/locking.rst |  7 ++++++-
 Documentation/filesystems/vfs.rst     | 14 ++++++++++++++
 include/linux/fs.h                    |  2 ++
 include/linux/pagemap.h               | 12 ++++++++++++
 mm/readahead.c                        | 13 ++++++++++++-
 5 files changed, 46 insertions(+), 2 deletions(-)

diff --git a/Documentation/filesystems/locking.rst b/Documentation/filesystems/locking.rst
index 5057e4d9dcd1..3d10729caf44 100644
--- a/Documentation/filesystems/locking.rst
+++ b/Documentation/filesystems/locking.rst
@@ -239,6 +239,8 @@ prototypes::
 	int (*readpage)(struct file *, struct page *);
 	int (*writepages)(struct address_space *, struct writeback_control *);
 	int (*set_page_dirty)(struct page *page);
+	unsigned (*readahead)(struct file *, struct address_space *,
+				 pgoff_t start, unsigned nr_pages);
 	int (*readpages)(struct file *filp, struct address_space *mapping,
 			struct list_head *pages, unsigned nr_pages);
 	int (*write_begin)(struct file *, struct address_space *mapping,
@@ -271,7 +273,8 @@ writepage:		yes, unlocks (see below)
 readpage:		yes, unlocks
 writepages:
 set_page_dirty		no
-readpages:
+readahead:		yes, unlocks
+readpages:		no
 write_begin:		locks the page		 exclusive
 write_end:		yes, unlocks		 exclusive
 bmap:
@@ -295,6 +298,8 @@ the request handler (/dev/loop).
 ->readpage() unlocks the page, either synchronously or via I/O
 completion.
 
+->readahead() unlocks the pages like ->readpage().
+
 ->readpages() populates the pagecache with the passed pages and starts
 I/O against them.  They come unlocked upon I/O completion.
 
diff --git a/Documentation/filesystems/vfs.rst b/Documentation/filesystems/vfs.rst
index 7d4d09dd5e6d..c2bc345f2169 100644
--- a/Documentation/filesystems/vfs.rst
+++ b/Documentation/filesystems/vfs.rst
@@ -706,6 +706,8 @@ cache in your filesystem.  The following members are defined:
 		int (*readpage)(struct file *, struct page *);
 		int (*writepages)(struct address_space *, struct writeback_control *);
 		int (*set_page_dirty)(struct page *page);
+		unsigned (*readahead)(struct file *filp, struct address_space *mapping,
+				 pgoff_t start, unsigned nr_pages);
 		int (*readpages)(struct file *filp, struct address_space *mapping,
 				 struct list_head *pages, unsigned nr_pages);
 		int (*write_begin)(struct file *, struct address_space *mapping,
@@ -781,6 +783,18 @@ cache in your filesystem.  The following members are defined:
 	If defined, it should set the PageDirty flag, and the
 	PAGECACHE_TAG_DIRTY tag in the radix tree.
 
+``readahead``
+	Called by the VM to read pages associated with the address_space
+	object.  The pages are consecutive in the page cache and
+	are locked.  The implementation should decrement the page
+	refcount after attempting I/O on each page.  Usually the
+	page will be unlocked by the I/O completion handler.  If the
+	function does not attempt I/O on some pages, return the number
+	of pages which were not read so the caller can unlock the pages
+	for you.  Set PageUptodate if the I/O completes successfully.
+	Setting PageError on any page will be ignored; simply unlock
+	the page if an I/O error occurs.
+
 ``readpages``
 	called by the VM to read pages associated with the address_space
 	object.  This is essentially just a vector version of readpage.
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 41584f50af0d..3bfc142e7d10 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -375,6 +375,8 @@ struct address_space_operations {
 	 */
 	int (*readpages)(struct file *filp, struct address_space *mapping,
 			struct list_head *pages, unsigned nr_pages);
+	unsigned (*readahead)(struct file *, struct address_space *,
+			pgoff_t start, unsigned nr_pages);
 
 	int (*write_begin)(struct file *, struct address_space *mapping,
 				loff_t pos, unsigned len, unsigned flags,
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index ccb14b6a16b5..a2cf007826f2 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -630,6 +630,18 @@ static inline int add_to_page_cache(struct page *page,
 	return error;
 }
 
+/*
+ * Only call this from a ->readahead implementation.
+ */
+static inline
+struct page *readahead_page(struct address_space *mapping, pgoff_t index)
+{
+	struct page *page = xa_load(&mapping->i_pages, index);
+	VM_BUG_ON_PAGE(!PageLocked(page), page);
+
+	return page;
+}
+
 static inline unsigned long dir_pages(struct inode *inode)
 {
 	return (unsigned long)(inode->i_size + PAGE_SIZE - 1) >>
diff --git a/mm/readahead.c b/mm/readahead.c
index 7daef0038b14..b2ed0baf3a5d 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -121,7 +121,18 @@ static void read_pages(struct address_space *mapping, struct file *filp,
 
 	blk_start_plug(&plug);
 
-	if (mapping->a_ops->readpages) {
+	if (mapping->a_ops->readahead) {
+		unsigned left = mapping->a_ops->readahead(filp, mapping,
+				start, nr_pages);
+
+		while (left) {
+			struct page *page = readahead_page(mapping,
+					start + nr_pages - left);
+			unlock_page(page);
+			put_page(page);
+			left--;
+		}
+	} else if (mapping->a_ops->readpages) {
 		mapping->a_ops->readpages(filp, mapping, pages, nr_pages);
 		/* Clean up the remaining pages */
 		put_pages_list(pages);
-- 
2.24.1

[PATCH v4 05/12] fs: Convert mpage_readpages to mpage_readahead

[Matthew Wilcox]

From: "Matthew Wilcox (Oracle)" <willy@infradead.org>

Implement the new readahead aop and convert all callers (block_dev,
exfat, ext2, fat, gfs2, hpfs, isofs, jfs, nilfs2, ocfs2, omfs, qnx6,
reiserfs & udf).  The callers are all trivial except for GFS2 & OCFS2.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: cluster-devel@redhat.com
Cc: ocfs2-devel@oss.oracle.com
---
 drivers/staging/exfat/exfat_super.c |  9 ++++---
 fs/block_dev.c                      |  9 ++++---
 fs/ext2/inode.c                     | 12 ++++-----
 fs/fat/inode.c                      |  8 +++---
 fs/gfs2/aops.c                      | 20 +++++++--------
 fs/hpfs/file.c                      |  8 +++---
 fs/iomap/buffered-io.c              |  2 +-
 fs/isofs/inode.c                    |  9 ++++---
 fs/jfs/inode.c                      |  8 +++---
 fs/mpage.c                          | 38 ++++++++++-------------------
 fs/nilfs2/inode.c                   | 13 +++++-----
 fs/ocfs2/aops.c                     | 32 +++++++++++-------------
 fs/omfs/file.c                      |  8 +++---
 fs/qnx6/inode.c                     |  8 +++---
 fs/reiserfs/inode.c                 | 10 ++++----
 fs/udf/inode.c                      |  8 +++---
 include/linux/mpage.h               |  2 +-
 mm/migrate.c                        |  2 +-
 18 files changed, 96 insertions(+), 110 deletions(-)

diff --git a/drivers/staging/exfat/exfat_super.c b/drivers/staging/exfat/exfat_super.c
index b81d2a87b82e..4dbfd8c84a1b 100644
--- a/drivers/staging/exfat/exfat_super.c
+++ b/drivers/staging/exfat/exfat_super.c
@@ -3002,10 +3002,11 @@ static int exfat_readpage(struct file *file, struct page *page)
 	return  mpage_readpage(page, exfat_get_block);
 }
 
-static int exfat_readpages(struct file *file, struct address_space *mapping,
-			   struct list_head *pages, unsigned int nr_pages)
+static
+unsigned exfat_readahead(struct file *file, struct address_space *mapping,
+			   pgoff_t start, unsigned int nr_pages)
 {
-	return  mpage_readpages(mapping, pages, nr_pages, exfat_get_block);
+	return  mpage_readahead(mapping, start, nr_pages, exfat_get_block);
 }
 
 static int exfat_writepage(struct page *page, struct writeback_control *wbc)
@@ -3104,7 +3105,7 @@ static sector_t _exfat_bmap(struct address_space *mapping, sector_t block)
 
 static const struct address_space_operations exfat_aops = {
 	.readpage    = exfat_readpage,
-	.readpages   = exfat_readpages,
+	.readahead   = exfat_readahead,
 	.writepage   = exfat_writepage,
 	.writepages  = exfat_writepages,
 	.write_begin = exfat_write_begin,
diff --git a/fs/block_dev.c b/fs/block_dev.c
index 69bf2fb6f7cd..826a5104ff56 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -614,10 +614,11 @@ static int blkdev_readpage(struct file * file, struct page * page)
 	return block_read_full_page(page, blkdev_get_block);
 }
 
-static int blkdev_readpages(struct file *file, struct address_space *mapping,
-			struct list_head *pages, unsigned nr_pages)
+static
+unsigned blkdev_readahead(struct file *file, struct address_space *mapping,
+			pgoff_t start, unsigned nr_pages)
 {
-	return mpage_readpages(mapping, pages, nr_pages, blkdev_get_block);
+	return mpage_readahead(mapping, start, nr_pages, blkdev_get_block);
 }
 
 static int blkdev_write_begin(struct file *file, struct address_space *mapping,
@@ -2062,7 +2063,7 @@ static int blkdev_writepages(struct address_space *mapping,
 
 static const struct address_space_operations def_blk_aops = {
 	.readpage	= blkdev_readpage,
-	.readpages	= blkdev_readpages,
+	.readahead	= blkdev_readahead,
 	.writepage	= blkdev_writepage,
 	.write_begin	= blkdev_write_begin,
 	.write_end	= blkdev_write_end,
diff --git a/fs/ext2/inode.c b/fs/ext2/inode.c
index 119667e65890..0440eb9f24de 100644
--- a/fs/ext2/inode.c
+++ b/fs/ext2/inode.c
@@ -877,11 +877,11 @@ static int ext2_readpage(struct file *file, struct page *page)
 	return mpage_readpage(page, ext2_get_block);
 }
 
-static int
-ext2_readpages(struct file *file, struct address_space *mapping,
-		struct list_head *pages, unsigned nr_pages)
+static unsigned
+ext2_readahead(struct file *file, struct address_space *mapping,
+		pgoff_t start, unsigned nr_pages)
 {
-	return mpage_readpages(mapping, pages, nr_pages, ext2_get_block);
+	return mpage_readahead(mapping, start, nr_pages, ext2_get_block);
 }
 
 static int
@@ -966,7 +966,7 @@ ext2_dax_writepages(struct address_space *mapping, struct writeback_control *wbc
 
 const struct address_space_operations ext2_aops = {
 	.readpage		= ext2_readpage,
-	.readpages		= ext2_readpages,
+	.readahead		= ext2_readahead,
 	.writepage		= ext2_writepage,
 	.write_begin		= ext2_write_begin,
 	.write_end		= ext2_write_end,
@@ -980,7 +980,7 @@ const struct address_space_operations ext2_aops = {
 
 const struct address_space_operations ext2_nobh_aops = {
 	.readpage		= ext2_readpage,
-	.readpages		= ext2_readpages,
+	.readahead		= ext2_readahead,
 	.writepage		= ext2_nobh_writepage,
 	.write_begin		= ext2_nobh_write_begin,
 	.write_end		= nobh_write_end,
diff --git a/fs/fat/inode.c b/fs/fat/inode.c
index 594b05ae16c9..a671dc6a122a 100644
--- a/fs/fat/inode.c
+++ b/fs/fat/inode.c
@@ -210,10 +210,10 @@ static int fat_readpage(struct file *file, struct page *page)
 	return mpage_readpage(page, fat_get_block);
 }
 
-static int fat_readpages(struct file *file, struct address_space *mapping,
-			 struct list_head *pages, unsigned nr_pages)
+static unsigned fat_readahead(struct file *file, struct address_space *mapping,
+			 pgoff_t start, unsigned nr_pages)
 {
-	return mpage_readpages(mapping, pages, nr_pages, fat_get_block);
+	return mpage_readahead(mapping, start, nr_pages, fat_get_block);
 }
 
 static void fat_write_failed(struct address_space *mapping, loff_t to)
@@ -344,7 +344,7 @@ int fat_block_truncate_page(struct inode *inode, loff_t from)
 
 static const struct address_space_operations fat_aops = {
 	.readpage	= fat_readpage,
-	.readpages	= fat_readpages,
+	.readahead	= fat_readahead,
 	.writepage	= fat_writepage,
 	.writepages	= fat_writepages,
 	.write_begin	= fat_write_begin,
diff --git a/fs/gfs2/aops.c b/fs/gfs2/aops.c
index ba83b49ce18c..5c6d89603f91 100644
--- a/fs/gfs2/aops.c
+++ b/fs/gfs2/aops.c
@@ -577,7 +577,7 @@ int gfs2_internal_read(struct gfs2_inode *ip, char *buf, loff_t *pos,
 }
 
 /**
- * gfs2_readpages - Read a bunch of pages at once
+ * gfs2_readahead - Read a bunch of pages at once
  * @file: The file to read from
  * @mapping: Address space info
  * @pages: List of pages to read
@@ -590,16 +590,15 @@ int gfs2_internal_read(struct gfs2_inode *ip, char *buf, loff_t *pos,
  *    obviously not something we'd want to do on too regular a basis.
  *    Any I/O we ignore at this time will be done via readpage later.
  * 2. We don't handle stuffed files here we let readpage do the honours.
- * 3. mpage_readpages() does most of the heavy lifting in the common case.
+ * 3. mpage_readahead() does most of the heavy lifting in the common case.
  * 4. gfs2_block_map() is relied upon to set BH_Boundary in the right places.
  */
 
-static int gfs2_readpages(struct file *file, struct address_space *mapping,
-			  struct list_head *pages, unsigned nr_pages)
+static unsigned gfs2_readahead(struct file *file, struct address_space *mapping,
+			  pgoff_t start, unsigned nr_pages)
 {
 	struct inode *inode = mapping->host;
 	struct gfs2_inode *ip = GFS2_I(inode);
-	struct gfs2_sbd *sdp = GFS2_SB(inode);
 	struct gfs2_holder gh;
 	int ret;
 
@@ -608,13 +607,12 @@ static int gfs2_readpages(struct file *file, struct address_space *mapping,
 	if (unlikely(ret))
 		goto out_uninit;
 	if (!gfs2_is_stuffed(ip))
-		ret = mpage_readpages(mapping, pages, nr_pages, gfs2_block_map);
+		nr_pages = mpage_readahead(mapping, start, nr_pages,
+				gfs2_block_map);
 	gfs2_glock_dq(&gh);
 out_uninit:
 	gfs2_holder_uninit(&gh);
-	if (unlikely(gfs2_withdrawn(sdp)))
-		ret = -EIO;
-	return ret;
+	return nr_pages;
 }
 
 /**
@@ -828,7 +826,7 @@ static const struct address_space_operations gfs2_aops = {
 	.writepage = gfs2_writepage,
 	.writepages = gfs2_writepages,
 	.readpage = gfs2_readpage,
-	.readpages = gfs2_readpages,
+	.readahead = gfs2_readahead,
 	.bmap = gfs2_bmap,
 	.invalidatepage = gfs2_invalidatepage,
 	.releasepage = gfs2_releasepage,
@@ -842,7 +840,7 @@ static const struct address_space_operations gfs2_jdata_aops = {
 	.writepage = gfs2_jdata_writepage,
 	.writepages = gfs2_jdata_writepages,
 	.readpage = gfs2_readpage,
-	.readpages = gfs2_readpages,
+	.readahead = gfs2_readahead,
 	.set_page_dirty = jdata_set_page_dirty,
 	.bmap = gfs2_bmap,
 	.invalidatepage = gfs2_invalidatepage,
diff --git a/fs/hpfs/file.c b/fs/hpfs/file.c
index b36abf9cb345..a0f7cc0262ae 100644
--- a/fs/hpfs/file.c
+++ b/fs/hpfs/file.c
@@ -125,10 +125,10 @@ static int hpfs_writepage(struct page *page, struct writeback_control *wbc)
 	return block_write_full_page(page, hpfs_get_block, wbc);
 }
 
-static int hpfs_readpages(struct file *file, struct address_space *mapping,
-			  struct list_head *pages, unsigned nr_pages)
+static unsigned hpfs_readahead(struct file *file, struct address_space *mapping,
+			  pgoff_t start, unsigned nr_pages)
 {
-	return mpage_readpages(mapping, pages, nr_pages, hpfs_get_block);
+	return mpage_readahead(mapping, start, nr_pages, hpfs_get_block);
 }
 
 static int hpfs_writepages(struct address_space *mapping,
@@ -198,7 +198,7 @@ static int hpfs_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
 const struct address_space_operations hpfs_aops = {
 	.readpage = hpfs_readpage,
 	.writepage = hpfs_writepage,
-	.readpages = hpfs_readpages,
+	.readahead = hpfs_readahead,
 	.writepages = hpfs_writepages,
 	.write_begin = hpfs_write_begin,
 	.write_end = hpfs_write_end,
diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index 7c84c4c027c4..cb3511eb152a 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -359,7 +359,7 @@ iomap_readpage(struct page *page, const struct iomap_ops *ops)
 	}
 
 	/*
-	 * Just like mpage_readpages and block_read_full_page we always
+	 * Just like mpage_readahead and block_read_full_page we always
 	 * return 0 and just mark the page as PageError on errors.  This
 	 * should be cleaned up all through the stack eventually.
 	 */
diff --git a/fs/isofs/inode.c b/fs/isofs/inode.c
index 62c0462dc89f..11154cc35b16 100644
--- a/fs/isofs/inode.c
+++ b/fs/isofs/inode.c
@@ -1185,10 +1185,11 @@ static int isofs_readpage(struct file *file, struct page *page)
 	return mpage_readpage(page, isofs_get_block);
 }
 
-static int isofs_readpages(struct file *file, struct address_space *mapping,
-			struct list_head *pages, unsigned nr_pages)
+static
+unsigned isofs_readahead(struct file *file, struct address_space *mapping,
+			pgoff_t start, unsigned nr_pages)
 {
-	return mpage_readpages(mapping, pages, nr_pages, isofs_get_block);
+	return mpage_readahead(mapping, start, nr_pages, isofs_get_block);
 }
 
 static sector_t _isofs_bmap(struct address_space *mapping, sector_t block)
@@ -1198,7 +1199,7 @@ static sector_t _isofs_bmap(struct address_space *mapping, sector_t block)
 
 static const struct address_space_operations isofs_aops = {
 	.readpage = isofs_readpage,
-	.readpages = isofs_readpages,
+	.readahead = isofs_readahead,
 	.bmap = _isofs_bmap
 };
 
diff --git a/fs/jfs/inode.c b/fs/jfs/inode.c
index 9486afcdac76..1ed926ac2bb9 100644
--- a/fs/jfs/inode.c
+++ b/fs/jfs/inode.c
@@ -296,10 +296,10 @@ static int jfs_readpage(struct file *file, struct page *page)
 	return mpage_readpage(page, jfs_get_block);
 }
 
-static int jfs_readpages(struct file *file, struct address_space *mapping,
-		struct list_head *pages, unsigned nr_pages)
+static unsigned jfs_readahead(struct file *file, struct address_space *mapping,
+		pgoff_t start, unsigned nr_pages)
 {
-	return mpage_readpages(mapping, pages, nr_pages, jfs_get_block);
+	return mpage_readahead(mapping, start, nr_pages, jfs_get_block);
 }
 
 static void jfs_write_failed(struct address_space *mapping, loff_t to)
@@ -358,7 +358,7 @@ static ssize_t jfs_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
 
 const struct address_space_operations jfs_aops = {
 	.readpage	= jfs_readpage,
-	.readpages	= jfs_readpages,
+	.readahead	= jfs_readahead,
 	.writepage	= jfs_writepage,
 	.writepages	= jfs_writepages,
 	.write_begin	= jfs_write_begin,
diff --git a/fs/mpage.c b/fs/mpage.c
index ccba3c4c4479..91a148bcd582 100644
--- a/fs/mpage.c
+++ b/fs/mpage.c
@@ -91,7 +91,7 @@ mpage_alloc(struct block_device *bdev,
 }
 
 /*
- * support function for mpage_readpages.  The fs supplied get_block might
+ * support function for mpage_readahead.  The fs supplied get_block might
  * return an up to date buffer.  This is used to map that buffer into
  * the page, which allows readpage to avoid triggering a duplicate call
  * to get_block.
@@ -338,13 +338,10 @@ static struct bio *do_mpage_readpage(struct mpage_readpage_args *args)
 }
 
 /**
- * mpage_readpages - populate an address space with some pages & start reads against them
+ * mpage_readahead - start reads against pages
  * @mapping: the address_space
- * @pages: The address of a list_head which contains the target pages.  These
- *   pages have their ->index populated and are otherwise uninitialised.
- *   The page at @pages->prev has the lowest file offset, and reads should be
- *   issued in @pages->prev to @pages->next order.
- * @nr_pages: The number of pages at *@pages
+ * @start: The number of the first page to read.
+ * @nr_pages: The number of consecutive pages to read.
  * @get_block: The filesystem's block mapper function.
  *
  * This function walks the pages and the blocks within each page, building and
@@ -381,36 +378,27 @@ static struct bio *do_mpage_readpage(struct mpage_readpage_args *args)
  *
  * This all causes the disk requests to be issued in the correct order.
  */
-int
-mpage_readpages(struct address_space *mapping, struct list_head *pages,
-				unsigned nr_pages, get_block_t get_block)
+unsigned mpage_readahead(struct address_space *mapping, pgoff_t start,
+		unsigned nr_pages, get_block_t get_block)
 {
 	struct mpage_readpage_args args = {
 		.get_block = get_block,
 		.is_readahead = true,
 	};
-	unsigned page_idx;
-
-	for (page_idx = 0; page_idx < nr_pages; page_idx++) {
-		struct page *page = lru_to_page(pages);
 
+	while (nr_pages--) {
+		struct page *page = readahead_page(mapping, start++);
 		prefetchw(&page->flags);
-		list_del(&page->lru);
-		if (!add_to_page_cache_lru(page, mapping,
-					page->index,
-					readahead_gfp_mask(mapping))) {
-			args.page = page;
-			args.nr_pages = nr_pages - page_idx;
-			args.bio = do_mpage_readpage(&args);
-		}
+		args.page = page;
+		args.nr_pages = nr_pages;
+		args.bio = do_mpage_readpage(&args);
 		put_page(page);
 	}
-	BUG_ON(!list_empty(pages));
 	if (args.bio)
 		mpage_bio_submit(REQ_OP_READ, REQ_RAHEAD, args.bio);
 	return 0;
 }
-EXPORT_SYMBOL(mpage_readpages);
+EXPORT_SYMBOL(mpage_readahead);
 
 /*
  * This isn't called much at all
@@ -563,7 +551,7 @@ static int __mpage_writepage(struct page *page, struct writeback_control *wbc,
 		 * Page has buffers, but they are all unmapped. The page was
 		 * created by pagein or read over a hole which was handled by
 		 * block_read_full_page().  If this address_space is also
-		 * using mpage_readpages then this can rarely happen.
+		 * using mpage_readahead then this can rarely happen.
 		 */
 		goto confused;
 	}
diff --git a/fs/nilfs2/inode.c b/fs/nilfs2/inode.c
index 671085512e0f..ecf543f35256 100644
--- a/fs/nilfs2/inode.c
+++ b/fs/nilfs2/inode.c
@@ -146,17 +146,18 @@ static int nilfs_readpage(struct file *file, struct page *page)
 }
 
 /**
- * nilfs_readpages() - implement readpages() method of nilfs_aops {}
+ * nilfs_readahead() - implement readahead() method of nilfs_aops {}
  * address_space_operations.
  * @file - file struct of the file to be read
  * @mapping - address_space struct used for reading multiple pages
- * @pages - the pages to be read
+ * @start - the first page to read
  * @nr_pages - number of pages to be read
  */
-static int nilfs_readpages(struct file *file, struct address_space *mapping,
-			   struct list_head *pages, unsigned int nr_pages)
+static
+unsigned nilfs_readahead(struct file *file, struct address_space *mapping,
+			   pgoff_t start, unsigned int nr_pages)
 {
-	return mpage_readpages(mapping, pages, nr_pages, nilfs_get_block);
+	return mpage_readahead(mapping, start, nr_pages, nilfs_get_block);
 }
 
 static int nilfs_writepages(struct address_space *mapping,
@@ -308,7 +309,7 @@ const struct address_space_operations nilfs_aops = {
 	.readpage		= nilfs_readpage,
 	.writepages		= nilfs_writepages,
 	.set_page_dirty		= nilfs_set_page_dirty,
-	.readpages		= nilfs_readpages,
+	.readahead		= nilfs_readahead,
 	.write_begin		= nilfs_write_begin,
 	.write_end		= nilfs_write_end,
 	/* .releasepage		= nilfs_releasepage, */
diff --git a/fs/ocfs2/aops.c b/fs/ocfs2/aops.c
index 3a67a6518ddf..a9784a6442b7 100644
--- a/fs/ocfs2/aops.c
+++ b/fs/ocfs2/aops.c
@@ -350,14 +350,13 @@ static int ocfs2_readpage(struct file *file, struct page *page)
  * grow out to a tree. If need be, detecting boundary extents could
  * trivially be added in a future version of ocfs2_get_block().
  */
-static int ocfs2_readpages(struct file *filp, struct address_space *mapping,
-			   struct list_head *pages, unsigned nr_pages)
+static
+unsigned ocfs2_readahead(struct file *filp, struct address_space *mapping,
+			   pgoff_t start, unsigned nr_pages)
 {
-	int ret, err = -EIO;
+	int ret;
 	struct inode *inode = mapping->host;
 	struct ocfs2_inode_info *oi = OCFS2_I(inode);
-	loff_t start;
-	struct page *last;
 
 	/*
 	 * Use the nonblocking flag for the dlm code to avoid page
@@ -365,36 +364,33 @@ static int ocfs2_readpages(struct file *filp, struct address_space *mapping,
 	 */
 	ret = ocfs2_inode_lock_full(inode, NULL, 0, OCFS2_LOCK_NONBLOCK);
 	if (ret)
-		return err;
+		return nr_pages;
 
-	if (down_read_trylock(&oi->ip_alloc_sem) == 0) {
-		ocfs2_inode_unlock(inode, 0);
-		return err;
-	}
+	if (down_read_trylock(&oi->ip_alloc_sem) == 0)
+		goto out_unlock;
 
 	/*
 	 * Don't bother with inline-data. There isn't anything
 	 * to read-ahead in that case anyway...
 	 */
 	if (oi->ip_dyn_features & OCFS2_INLINE_DATA_FL)
-		goto out_unlock;
+		goto out_up;
 
 	/*
 	 * Check whether a remote node truncated this file - we just
 	 * drop out in that case as it's not worth handling here.
 	 */
-	last = lru_to_page(pages);
-	start = (loff_t)last->index << PAGE_SHIFT;
 	if (start >= i_size_read(inode))
-		goto out_unlock;
+		goto out_up;
 
-	err = mpage_readpages(mapping, pages, nr_pages, ocfs2_get_block);
+	nr_pages = mpage_readahead(mapping, start, nr_pages, ocfs2_get_block);
 
-out_unlock:
+out_up:
 	up_read(&oi->ip_alloc_sem);
+out_unlock:
 	ocfs2_inode_unlock(inode, 0);
 
-	return err;
+	return nr_pages;
 }
 
 /* Note: Because we don't support holes, our allocation has
@@ -2474,7 +2470,7 @@ static ssize_t ocfs2_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
 
 const struct address_space_operations ocfs2_aops = {
 	.readpage		= ocfs2_readpage,
-	.readpages		= ocfs2_readpages,
+	.readahead		= ocfs2_readahead,
 	.writepage		= ocfs2_writepage,
 	.write_begin		= ocfs2_write_begin,
 	.write_end		= ocfs2_write_end,
diff --git a/fs/omfs/file.c b/fs/omfs/file.c
index d640b9388238..e7392f49f619 100644
--- a/fs/omfs/file.c
+++ b/fs/omfs/file.c
@@ -289,10 +289,10 @@ static int omfs_readpage(struct file *file, struct page *page)
 	return block_read_full_page(page, omfs_get_block);
 }
 
-static int omfs_readpages(struct file *file, struct address_space *mapping,
-		struct list_head *pages, unsigned nr_pages)
+static unsigned omfs_readahead(struct file *file, struct address_space *mapping,
+		pgoff_t start, unsigned nr_pages)
 {
-	return mpage_readpages(mapping, pages, nr_pages, omfs_get_block);
+	return mpage_readahead(mapping, start, nr_pages, omfs_get_block);
 }
 
 static int omfs_writepage(struct page *page, struct writeback_control *wbc)
@@ -373,7 +373,7 @@ const struct inode_operations omfs_file_inops = {
 
 const struct address_space_operations omfs_aops = {
 	.readpage = omfs_readpage,
-	.readpages = omfs_readpages,
+	.readahead = omfs_readahead,
 	.writepage = omfs_writepage,
 	.writepages = omfs_writepages,
 	.write_begin = omfs_write_begin,
diff --git a/fs/qnx6/inode.c b/fs/qnx6/inode.c
index 345db56c98fd..949e823a1d30 100644
--- a/fs/qnx6/inode.c
+++ b/fs/qnx6/inode.c
@@ -99,10 +99,10 @@ static int qnx6_readpage(struct file *file, struct page *page)
 	return mpage_readpage(page, qnx6_get_block);
 }
 
-static int qnx6_readpages(struct file *file, struct address_space *mapping,
-		   struct list_head *pages, unsigned nr_pages)
+static unsigned qnx6_readahead(struct file *file, struct address_space *mapping,
+		   pgoff_t start, unsigned nr_pages)
 {
-	return mpage_readpages(mapping, pages, nr_pages, qnx6_get_block);
+	return mpage_readahead(mapping, start, nr_pages, qnx6_get_block);
 }
 
 /*
@@ -499,7 +499,7 @@ static sector_t qnx6_bmap(struct address_space *mapping, sector_t block)
 }
 static const struct address_space_operations qnx6_aops = {
 	.readpage	= qnx6_readpage,
-	.readpages	= qnx6_readpages,
+	.readahead	= qnx6_readahead,
 	.bmap		= qnx6_bmap
 };
 
diff --git a/fs/reiserfs/inode.c b/fs/reiserfs/inode.c
index 6419e6dacc39..0f2666ef23dd 100644
--- a/fs/reiserfs/inode.c
+++ b/fs/reiserfs/inode.c
@@ -1160,11 +1160,11 @@ int reiserfs_get_block(struct inode *inode, sector_t block,
 	return retval;
 }
 
-static int
-reiserfs_readpages(struct file *file, struct address_space *mapping,
-		   struct list_head *pages, unsigned nr_pages)
+static unsigned
+reiserfs_readahead(struct file *file, struct address_space *mapping,
+		   pgoff_t start, unsigned nr_pages)
 {
-	return mpage_readpages(mapping, pages, nr_pages, reiserfs_get_block);
+	return mpage_readahead(mapping, start, nr_pages, reiserfs_get_block);
 }
 
 /*
@@ -3434,7 +3434,7 @@ int reiserfs_setattr(struct dentry *dentry, struct iattr *attr)
 const struct address_space_operations reiserfs_address_space_operations = {
 	.writepage = reiserfs_writepage,
 	.readpage = reiserfs_readpage,
-	.readpages = reiserfs_readpages,
+	.readahead = reiserfs_readahead,
 	.releasepage = reiserfs_releasepage,
 	.invalidatepage = reiserfs_invalidatepage,
 	.write_begin = reiserfs_write_begin,
diff --git a/fs/udf/inode.c b/fs/udf/inode.c
index e875bc5668ee..97c9bccf1be4 100644
--- a/fs/udf/inode.c
+++ b/fs/udf/inode.c
@@ -195,10 +195,10 @@ static int udf_readpage(struct file *file, struct page *page)
 	return mpage_readpage(page, udf_get_block);
 }
 
-static int udf_readpages(struct file *file, struct address_space *mapping,
-			struct list_head *pages, unsigned nr_pages)
+static unsigned udf_readahead(struct file *file, struct address_space *mapping,
+			pgoff_t start, unsigned nr_pages)
 {
-	return mpage_readpages(mapping, pages, nr_pages, udf_get_block);
+	return mpage_readahead(mapping, start, nr_pages, udf_get_block);
 }
 
 static int udf_write_begin(struct file *file, struct address_space *mapping,
@@ -234,7 +234,7 @@ static sector_t udf_bmap(struct address_space *mapping, sector_t block)
 
 const struct address_space_operations udf_aops = {
 	.readpage	= udf_readpage,
-	.readpages	= udf_readpages,
+	.readahead	= udf_readahead,
 	.writepage	= udf_writepage,
 	.writepages	= udf_writepages,
 	.write_begin	= udf_write_begin,
diff --git a/include/linux/mpage.h b/include/linux/mpage.h
index 001f1fcf9836..dabf7b5a6a28 100644
--- a/include/linux/mpage.h
+++ b/include/linux/mpage.h
@@ -14,7 +14,7 @@
 
 struct writeback_control;
 
-int mpage_readpages(struct address_space *mapping, struct list_head *pages,
+unsigned mpage_readahead(struct address_space *mapping, pgoff_t start,
 				unsigned nr_pages, get_block_t get_block);
 int mpage_readpage(struct page *page, get_block_t get_block);
 int mpage_writepages(struct address_space *mapping,
diff --git a/mm/migrate.c b/mm/migrate.c
index edf42ed90030..860925dd2725 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1020,7 +1020,7 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
 		 * to the LRU. Later, when the IO completes the pages are
 		 * marked uptodate and unlocked. However, the queueing
 		 * could be merging multiple pages for one bio (e.g.
-		 * mpage_readpages). If an allocation happens for the
+		 * mpage_readahead). If an allocation happens for the
 		 * second or third page, the process can end up locking
 		 * the same page twice and deadlocking. Rather than
 		 * trying to be clever about what pages can be locked,
-- 
2.24.1

[PATCH v4 06/12] btrfs: Convert from readpages to readahead

[Matthew Wilcox]

From: "Matthew Wilcox (Oracle)" <willy@infradead.org>

Use the new readahead operation in btrfs

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: linux-btrfs@vger.kernel.org
---
 fs/btrfs/extent_io.c | 19 +++++++------------
 fs/btrfs/extent_io.h |  2 +-
 fs/btrfs/inode.c     | 18 +++++++++---------
 3 files changed, 17 insertions(+), 22 deletions(-)

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index e2d30287e2d5..18b1fbfdcab2 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -4269,7 +4269,7 @@ int extent_writepages(struct address_space *mapping,
 	return ret;
 }
 
-int extent_readpages(struct address_space *mapping, struct list_head *pages,
+unsigned extent_readahead(struct address_space *mapping, pgoff_t start,
 		     unsigned nr_pages)
 {
 	struct bio *bio = NULL;
@@ -4280,22 +4280,17 @@ int extent_readpages(struct address_space *mapping, struct list_head *pages,
 	int nr = 0;
 	u64 prev_em_start = (u64)-1;
 
-	while (!list_empty(pages)) {
+	while (nr_pages) {
 		u64 contig_end = 0;
 
-		for (nr = 0; nr < ARRAY_SIZE(pagepool) && !list_empty(pages);) {
-			struct page *page = lru_to_page(pages);
+		for (nr = 0; nr < ARRAY_SIZE(pagepool); nr++) {
+			struct page *page = readahead_page(mapping, start++);
 
 			prefetchw(&page->flags);
-			list_del(&page->lru);
-			if (add_to_page_cache_lru(page, mapping, page->index,
-						readahead_gfp_mask(mapping))) {
-				put_page(page);
-				break;
-			}
-
-			pagepool[nr++] = page;
+			pagepool[nr] = page;
 			contig_end = page_offset(page) + PAGE_SIZE - 1;
+			if (--nr_pages == 0)
+				break;
 		}
 
 		if (nr) {
diff --git a/fs/btrfs/extent_io.h b/fs/btrfs/extent_io.h
index 5d205bbaafdc..4fd9dc05592b 100644
--- a/fs/btrfs/extent_io.h
+++ b/fs/btrfs/extent_io.h
@@ -198,7 +198,7 @@ int extent_writepages(struct address_space *mapping,
 		      struct writeback_control *wbc);
 int btree_write_cache_pages(struct address_space *mapping,
 			    struct writeback_control *wbc);
-int extent_readpages(struct address_space *mapping, struct list_head *pages,
+unsigned extent_readahead(struct address_space *mapping, pgoff_t start,
 		     unsigned nr_pages);
 int extent_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
 		__u64 start, __u64 len);
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 6d2bb58d277a..7622918d7624 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -4723,8 +4723,8 @@ static void evict_inode_truncate_pages(struct inode *inode)
 
 	/*
 	 * Keep looping until we have no more ranges in the io tree.
-	 * We can have ongoing bios started by readpages (called from readahead)
-	 * that have their endio callback (extent_io.c:end_bio_extent_readpage)
+	 * We can have ongoing bios started by readahead that have
+	 * their endio callback (extent_io.c:end_bio_extent_readpage)
 	 * still in progress (unlocked the pages in the bio but did not yet
 	 * unlocked the ranges in the io tree). Therefore this means some
 	 * ranges can still be locked and eviction started because before
@@ -6925,11 +6925,11 @@ static int lock_extent_direct(struct inode *inode, u64 lockstart, u64 lockend,
 			 * for it to complete) and then invalidate the pages for
 			 * this range (through invalidate_inode_pages2_range()),
 			 * but that can lead us to a deadlock with a concurrent
-			 * call to readpages() (a buffered read or a defrag call
+			 * call to readahead (a buffered read or a defrag call
 			 * triggered a readahead) on a page lock due to an
 			 * ordered dio extent we created before but did not have
 			 * yet a corresponding bio submitted (whence it can not
-			 * complete), which makes readpages() wait for that
+			 * complete), which makes readahead wait for that
 			 * ordered extent to complete while holding a lock on
 			 * that page.
 			 */
@@ -8168,11 +8168,11 @@ static int btrfs_writepages(struct address_space *mapping,
 	return extent_writepages(mapping, wbc);
 }
 
-static int
-btrfs_readpages(struct file *file, struct address_space *mapping,
-		struct list_head *pages, unsigned nr_pages)
+static unsigned
+btrfs_readahead(struct file *file, struct address_space *mapping,
+		pgoff_t start, unsigned nr_pages)
 {
-	return extent_readpages(mapping, pages, nr_pages);
+	return extent_readahead(mapping, start, nr_pages);
 }
 
 static int __btrfs_releasepage(struct page *page, gfp_t gfp_flags)
@@ -10377,7 +10377,7 @@ static const struct address_space_operations btrfs_aops = {
 	.readpage	= btrfs_readpage,
 	.writepage	= btrfs_writepage,
 	.writepages	= btrfs_writepages,
-	.readpages	= btrfs_readpages,
+	.readahead	= btrfs_readahead,
 	.direct_IO	= btrfs_direct_IO,
 	.invalidatepage = btrfs_invalidatepage,
 	.releasepage	= btrfs_releasepage,
-- 
2.24.1

[PATCH v4 07/12] erofs: Convert uncompressed files from readpages to readahead

[Matthew Wilcox]

From: "Matthew Wilcox (Oracle)" <willy@infradead.org>

Use the new readahead operation in erofs

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: linux-erofs@lists.ozlabs.org
---
 fs/erofs/data.c              | 33 +++++++++++++--------------------
 fs/erofs/zdata.c             |  2 +-
 include/trace/events/erofs.h |  6 +++---
 3 files changed, 17 insertions(+), 24 deletions(-)

diff --git a/fs/erofs/data.c b/fs/erofs/data.c
index fc3a8d8064f8..514b43463a21 100644
--- a/fs/erofs/data.c
+++ b/fs/erofs/data.c
@@ -280,42 +280,35 @@ static int erofs_raw_access_readpage(struct file *file, struct page *page)
 	return 0;
 }
 
-static int erofs_raw_access_readpages(struct file *filp,
+static unsigned erofs_raw_access_readahead(struct file *file,
 				      struct address_space *mapping,
-				      struct list_head *pages,
+				      pgoff_t start,
 				      unsigned int nr_pages)
 {
 	erofs_off_t last_block;
 	struct bio *bio = NULL;
-	gfp_t gfp = readahead_gfp_mask(mapping);
-	struct page *page = list_last_entry(pages, struct page, lru);
 
-	trace_erofs_readpages(mapping->host, page, nr_pages, true);
+	trace_erofs_readpages(mapping->host, start, nr_pages, true);
 
 	for (; nr_pages; --nr_pages) {
-		page = list_entry(pages->prev, struct page, lru);
+		struct page *page = readahead_page(mapping, start++);
 
 		prefetchw(&page->flags);
-		list_del(&page->lru);
 
-		if (!add_to_page_cache_lru(page, mapping, page->index, gfp)) {
-			bio = erofs_read_raw_page(bio, mapping, page,
-						  &last_block, nr_pages, true);
+		bio = erofs_read_raw_page(bio, mapping, page, &last_block,
+				nr_pages, true);
 
-			/* all the page errors are ignored when readahead */
-			if (IS_ERR(bio)) {
-				pr_err("%s, readahead error at page %lu of nid %llu\n",
-				       __func__, page->index,
-				       EROFS_I(mapping->host)->nid);
+		/* all the page errors are ignored when readahead */
+		if (IS_ERR(bio)) {
+			pr_err("%s, readahead error at page %lu of nid %llu\n",
+			       __func__, page->index,
+			       EROFS_I(mapping->host)->nid);
 
-				bio = NULL;
-			}
+			bio = NULL;
 		}
 
-		/* pages could still be locked */
 		put_page(page);
 	}
-	DBG_BUGON(!list_empty(pages));
 
 	/* the rare case (end in gaps) */
 	if (bio)
@@ -358,7 +351,7 @@ static sector_t erofs_bmap(struct address_space *mapping, sector_t block)
 /* for uncompressed (aligned) files and raw access for other files */
 const struct address_space_operations erofs_raw_access_aops = {
 	.readpage = erofs_raw_access_readpage,
-	.readpages = erofs_raw_access_readpages,
+	.readahead = erofs_raw_access_readahead,
 	.bmap = erofs_bmap,
 };
 
diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
index 80e47f07d946..17f45fcb8c5c 100644
--- a/fs/erofs/zdata.c
+++ b/fs/erofs/zdata.c
@@ -1315,7 +1315,7 @@ static int z_erofs_readpages(struct file *filp, struct address_space *mapping,
 	struct page *head = NULL;
 	LIST_HEAD(pagepool);
 
-	trace_erofs_readpages(mapping->host, lru_to_page(pages),
+	trace_erofs_readpages(mapping->host, lru_to_page(pages)->index,
 			      nr_pages, false);
 
 	f.headoffset = (erofs_off_t)lru_to_page(pages)->index << PAGE_SHIFT;
diff --git a/include/trace/events/erofs.h b/include/trace/events/erofs.h
index 27f5caa6299a..bf9806fd1306 100644
--- a/include/trace/events/erofs.h
+++ b/include/trace/events/erofs.h
@@ -113,10 +113,10 @@ TRACE_EVENT(erofs_readpage,
 
 TRACE_EVENT(erofs_readpages,
 
-	TP_PROTO(struct inode *inode, struct page *page, unsigned int nrpage,
+	TP_PROTO(struct inode *inode, pgoff_t start, unsigned int nrpage,
 		bool raw),
 
-	TP_ARGS(inode, page, nrpage, raw),
+	TP_ARGS(inode, start, nrpage, raw),
 
 	TP_STRUCT__entry(
 		__field(dev_t,		dev	)
@@ -129,7 +129,7 @@ TRACE_EVENT(erofs_readpages,
 	TP_fast_assign(
 		__entry->dev	= inode->i_sb->s_dev;
 		__entry->nid	= EROFS_I(inode)->nid;
-		__entry->start	= page->index;
+		__entry->start	= start;
 		__entry->nrpage	= nrpage;
 		__entry->raw	= raw;
 	),
-- 
2.24.1

[PATCH v4 08/12] erofs: Convert compressed files from readpages to readahead

[Matthew Wilcox]

From: "Matthew Wilcox (Oracle)" <willy@infradead.org>

Use the new readahead operation in erofs.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: linux-erofs@lists.ozlabs.org
---
 fs/erofs/zdata.c | 21 +++++++--------------
 1 file changed, 7 insertions(+), 14 deletions(-)

diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
index 17f45fcb8c5c..97c05200a784 100644
--- a/fs/erofs/zdata.c
+++ b/fs/erofs/zdata.c
@@ -1303,28 +1303,26 @@ static bool should_decompress_synchronously(struct erofs_sb_info *sbi,
 	return nr <= sbi->max_sync_decompress_pages;
 }
 
-static int z_erofs_readpages(struct file *filp, struct address_space *mapping,
-			     struct list_head *pages, unsigned int nr_pages)
+static
+unsigned z_erofs_readahead(struct file *file, struct address_space *mapping,
+			     pgoff_t start, unsigned int nr_pages)
 {
 	struct inode *const inode = mapping->host;
 	struct erofs_sb_info *const sbi = EROFS_I_SB(inode);
 
 	bool sync = should_decompress_synchronously(sbi, nr_pages);
 	struct z_erofs_decompress_frontend f = DECOMPRESS_FRONTEND_INIT(inode);
-	gfp_t gfp = mapping_gfp_constraint(mapping, GFP_KERNEL);
 	struct page *head = NULL;
 	LIST_HEAD(pagepool);
 
-	trace_erofs_readpages(mapping->host, lru_to_page(pages)->index,
-			      nr_pages, false);
+	trace_erofs_readpages(inode, start, nr_pages, false);
 
-	f.headoffset = (erofs_off_t)lru_to_page(pages)->index << PAGE_SHIFT;
+	f.headoffset = (erofs_off_t)start << PAGE_SHIFT;
 
 	for (; nr_pages; --nr_pages) {
-		struct page *page = lru_to_page(pages);
+		struct page *page = readahead_page(mapping, start);
 
 		prefetchw(&page->flags);
-		list_del(&page->lru);
 
 		/*
 		 * A pure asynchronous readahead is indicated if
@@ -1333,11 +1331,6 @@ static int z_erofs_readpages(struct file *filp, struct address_space *mapping,
 		 */
 		sync &= !(PageReadahead(page) && !head);
 
-		if (add_to_page_cache_lru(page, mapping, page->index, gfp)) {
-			list_add(&page->lru, &pagepool);
-			continue;
-		}
-
 		set_page_private(page, (unsigned long)head);
 		head = page;
 	}
@@ -1371,6 +1364,6 @@ static int z_erofs_readpages(struct file *filp, struct address_space *mapping,
 
 const struct address_space_operations z_erofs_aops = {
 	.readpage = z_erofs_readpage,
-	.readpages = z_erofs_readpages,
+	.readahead = z_erofs_readahead,
 };
 
-- 
2.24.1

[PATCH v4 09/12] ext4: Convert from readpages to readahead

[Matthew Wilcox]

From: "Matthew Wilcox (Oracle)" <willy@infradead.org>

Use the new readahead operation in ext4

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: linux-ext4@vger.kernel.org
---
 fs/ext4/ext4.h     |  5 ++---
 fs/ext4/inode.c    | 24 ++++++++++++------------
 fs/ext4/readpage.c | 20 +++++++-------------
 fs/ext4/verity.c   | 16 +++++++++++-----
 4 files changed, 32 insertions(+), 33 deletions(-)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 9a2ee2428ecc..346ad9e1403b 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -3275,9 +3275,8 @@ static inline void ext4_set_de_type(struct super_block *sb,
 }
 
 /* readpages.c */
-extern int ext4_mpage_readpages(struct address_space *mapping,
-				struct list_head *pages, struct page *page,
-				unsigned nr_pages, bool is_readahead);
+extern int ext4_mpage_readpages(struct address_space *mapping, pgoff_t start,
+		struct page *page, unsigned nr_pages, bool is_readahead);
 extern int __init ext4_init_post_read_processing(void);
 extern void ext4_exit_post_read_processing(void);
 
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 3313168b680f..e1f5864e5ecf 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3218,7 +3218,7 @@ static sector_t ext4_bmap(struct address_space *mapping, sector_t block)
 static int ext4_readpage(struct file *file, struct page *page)
 {
 	int ret = -EAGAIN;
-	struct inode *inode = page->mapping->host;
+	struct inode *inode = file_inode(file);
 
 	trace_ext4_readpage(page);
 
@@ -3226,23 +3226,23 @@ static int ext4_readpage(struct file *file, struct page *page)
 		ret = ext4_readpage_inline(inode, page);
 
 	if (ret == -EAGAIN)
-		return ext4_mpage_readpages(page->mapping, NULL, page, 1,
-						false);
+		return ext4_mpage_readpages(page->mapping, 0, page, 1, false);
 
 	return ret;
 }
 
-static int
-ext4_readpages(struct file *file, struct address_space *mapping,
-		struct list_head *pages, unsigned nr_pages)
+static unsigned
+ext4_readahead(struct file *file, struct address_space *mapping,
+		pgoff_t start, unsigned nr_pages)
 {
 	struct inode *inode = mapping->host;
 
-	/* If the file has inline data, no need to do readpages. */
+	/* If the file has inline data, no need to do readahead. */
 	if (ext4_has_inline_data(inode))
-		return 0;
+		return nr_pages;
 
-	return ext4_mpage_readpages(mapping, pages, NULL, nr_pages, true);
+	ext4_mpage_readpages(mapping, start, NULL, nr_pages, true);
+	return 0;
 }
 
 static void ext4_invalidatepage(struct page *page, unsigned int offset,
@@ -3587,7 +3587,7 @@ static int ext4_set_page_dirty(struct page *page)
 
 static const struct address_space_operations ext4_aops = {
 	.readpage		= ext4_readpage,
-	.readpages		= ext4_readpages,
+	.readahead		= ext4_readahead,
 	.writepage		= ext4_writepage,
 	.writepages		= ext4_writepages,
 	.write_begin		= ext4_write_begin,
@@ -3604,7 +3604,7 @@ static const struct address_space_operations ext4_aops = {
 
 static const struct address_space_operations ext4_journalled_aops = {
 	.readpage		= ext4_readpage,
-	.readpages		= ext4_readpages,
+	.readahead		= ext4_readahead,
 	.writepage		= ext4_writepage,
 	.writepages		= ext4_writepages,
 	.write_begin		= ext4_write_begin,
@@ -3620,7 +3620,7 @@ static const struct address_space_operations ext4_journalled_aops = {
 
 static const struct address_space_operations ext4_da_aops = {
 	.readpage		= ext4_readpage,
-	.readpages		= ext4_readpages,
+	.readahead		= ext4_readahead,
 	.writepage		= ext4_writepage,
 	.writepages		= ext4_writepages,
 	.write_begin		= ext4_da_write_begin,
diff --git a/fs/ext4/readpage.c b/fs/ext4/readpage.c
index c1769afbf799..aaeb298c8fdb 100644
--- a/fs/ext4/readpage.c
+++ b/fs/ext4/readpage.c
@@ -7,8 +7,8 @@
  *
  * This was originally taken from fs/mpage.c
  *
- * The intent is the ext4_mpage_readpages() function here is intended
- * to replace mpage_readpages() in the general case, not just for
+ * The ext4_mpage_readahead() function here is intended to
+ * replace mpage_readahead() in the general case, not just for
  * encrypted files.  It has some limitations (see below), where it
  * will fall back to read_block_full_page(), but these limitations
  * should only be hit when page_size != block_size.
@@ -221,9 +221,8 @@ static inline loff_t ext4_readpage_limit(struct inode *inode)
 	return i_size_read(inode);
 }
 
-int ext4_mpage_readpages(struct address_space *mapping,
-			 struct list_head *pages, struct page *page,
-			 unsigned nr_pages, bool is_readahead)
+int ext4_mpage_readpages(struct address_space *mapping, pgoff_t start,
+		struct page *page, unsigned nr_pages, bool is_readahead)
 {
 	struct bio *bio = NULL;
 	sector_t last_block_in_bio = 0;
@@ -251,14 +250,10 @@ int ext4_mpage_readpages(struct address_space *mapping,
 		int fully_mapped = 1;
 		unsigned first_hole = blocks_per_page;
 
-		if (pages) {
-			page = lru_to_page(pages);
+		if (is_readahead) {
+			page = readahead_page(mapping, start++);
 
 			prefetchw(&page->flags);
-			list_del(&page->lru);
-			if (add_to_page_cache_lru(page, mapping, page->index,
-				  readahead_gfp_mask(mapping)))
-				goto next_page;
 		}
 
 		if (page_has_buffers(page))
@@ -406,10 +401,9 @@ int ext4_mpage_readpages(struct address_space *mapping,
 		else
 			unlock_page(page);
 	next_page:
-		if (pages)
+		if (is_readahead)
 			put_page(page);
 	}
-	BUG_ON(pages && !list_empty(pages));
 	if (bio)
 		submit_bio(bio);
 	return 0;
diff --git a/fs/ext4/verity.c b/fs/ext4/verity.c
index dc5ec724d889..40a550c0da2b 100644
--- a/fs/ext4/verity.c
+++ b/fs/ext4/verity.c
@@ -351,7 +351,6 @@ static int ext4_get_verity_descriptor(struct inode *inode, void *buf,
 static void ext4_merkle_tree_readahead(struct address_space *mapping,
 				       pgoff_t start_index, unsigned long count)
 {
-	LIST_HEAD(pages);
 	unsigned int nr_pages = 0;
 	struct page *page;
 	pgoff_t index;
@@ -360,16 +359,23 @@ static void ext4_merkle_tree_readahead(struct address_space *mapping,
 	for (index = start_index; index < start_index + count; index++) {
 		page = xa_load(&mapping->i_pages, index);
 		if (!page || xa_is_value(page)) {
-			page = __page_cache_alloc(readahead_gfp_mask(mapping));
+			gfp_t gfp = readahead_gfp_mask(mapping);
+			page = __page_cache_alloc(gfp);
 			if (!page)
 				break;
-			page->index = index;
-			list_add(&page->lru, &pages);
+			if (add_to_page_cache_lru(page, mapping, index, gfp)) {
+				put_page(page);
+				break;
+			}
 			nr_pages++;
 		}
 	}
+
+	if (!nr_pages)
+		return;
+
 	blk_start_plug(&plug);
-	ext4_mpage_readpages(mapping, &pages, NULL, nr_pages, true);
+	ext4_mpage_readpages(mapping, start_index, NULL, nr_pages, true);
 	blk_finish_plug(&plug);
 }
 
-- 
2.24.1

[PATCH v4 10/12] f2fs: Convert from readpages to readahead

[Matthew Wilcox]

From: "Matthew Wilcox (Oracle)" <willy@infradead.org>

Use the new readahead operation in f2fs

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: linux-f2fs-devel@lists.sourceforge.net
---
 fs/f2fs/data.c              | 35 ++++++++++++++---------------------
 fs/f2fs/f2fs.h              |  5 ++---
 fs/f2fs/verity.c            | 16 +++++++++++-----
 include/trace/events/f2fs.h |  6 +++---
 4 files changed, 30 insertions(+), 32 deletions(-)

diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index 8bd9afa81c54..80803f8b1b40 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -2159,9 +2159,8 @@ int f2fs_read_multi_pages(struct compress_ctx *cc, struct bio **bio_ret,
  * use ->readpage() or do the necessary surgery to decouple ->readpages()
  * from read-ahead.
  */
-int f2fs_mpage_readpages(struct address_space *mapping,
-			struct list_head *pages, struct page *page,
-			unsigned nr_pages, bool is_readahead)
+int f2fs_mpage_readpages(struct address_space *mapping, pgoff_t start,
+		struct page *page, unsigned nr_pages, bool is_readahead)
 {
 	struct bio *bio = NULL;
 	sector_t last_block_in_bio = 0;
@@ -2192,15 +2191,10 @@ int f2fs_mpage_readpages(struct address_space *mapping,
 	map.m_may_create = false;
 
 	for (; nr_pages; nr_pages--) {
-		if (pages) {
-			page = list_last_entry(pages, struct page, lru);
+		if (is_readahead) {
+			page = readahead_page(mapping, start++);
 
 			prefetchw(&page->flags);
-			list_del(&page->lru);
-			if (add_to_page_cache_lru(page, mapping,
-						  page_index(page),
-						  readahead_gfp_mask(mapping)))
-				goto next_page;
 		}
 
 #ifdef CONFIG_F2FS_FS_COMPRESSION
@@ -2243,7 +2237,7 @@ int f2fs_mpage_readpages(struct address_space *mapping,
 			unlock_page(page);
 		}
 next_page:
-		if (pages)
+		if (is_readahead)
 			put_page(page);
 
 #ifdef CONFIG_F2FS_FS_COMPRESSION
@@ -2259,10 +2253,9 @@ int f2fs_mpage_readpages(struct address_space *mapping,
 		}
 #endif
 	}
-	BUG_ON(pages && !list_empty(pages));
 	if (bio)
 		__submit_bio(F2FS_I_SB(inode), bio, DATA);
-	return pages ? 0 : ret;
+	return ret;
 }
 
 static int f2fs_read_data_page(struct file *file, struct page *page)
@@ -2282,27 +2275,27 @@ static int f2fs_read_data_page(struct file *file, struct page *page)
 		ret = f2fs_read_inline_data(inode, page);
 	if (ret == -EAGAIN)
 		ret = f2fs_mpage_readpages(page_file_mapping(page),
-						NULL, page, 1, false);
+						0, page, 1, false);
 	return ret;
 }
 
-static int f2fs_read_data_pages(struct file *file,
+static unsigned f2fs_readahead(struct file *file,
 			struct address_space *mapping,
-			struct list_head *pages, unsigned nr_pages)
+			pgoff_t start, unsigned nr_pages)
 {
 	struct inode *inode = mapping->host;
-	struct page *page = list_last_entry(pages, struct page, lru);
 
-	trace_f2fs_readpages(inode, page, nr_pages);
+	trace_f2fs_readpages(inode, start, nr_pages);
 
 	if (!f2fs_is_compress_backend_ready(inode))
 		return 0;
 
 	/* If the file has inline data, skip readpages */
 	if (f2fs_has_inline_data(inode))
-		return 0;
+		return nr_pages;
 
-	return f2fs_mpage_readpages(mapping, pages, NULL, nr_pages, true);
+	f2fs_mpage_readpages(mapping, start, NULL, nr_pages, true);
+	return 0;
 }
 
 int f2fs_encrypt_one_page(struct f2fs_io_info *fio)
@@ -3778,7 +3771,7 @@ static void f2fs_swap_deactivate(struct file *file)
 
 const struct address_space_operations f2fs_dblock_aops = {
 	.readpage	= f2fs_read_data_page,
-	.readpages	= f2fs_read_data_pages,
+	.readahead	= f2fs_readahead,
 	.writepage	= f2fs_write_data_page,
 	.writepages	= f2fs_write_data_pages,
 	.write_begin	= f2fs_write_begin,
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 5355be6b6755..db00907f90f1 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -3344,9 +3344,8 @@ int f2fs_reserve_new_block(struct dnode_of_data *dn);
 int f2fs_get_block(struct dnode_of_data *dn, pgoff_t index);
 int f2fs_preallocate_blocks(struct kiocb *iocb, struct iov_iter *from);
 int f2fs_reserve_block(struct dnode_of_data *dn, pgoff_t index);
-int f2fs_mpage_readpages(struct address_space *mapping,
-			struct list_head *pages, struct page *page,
-			unsigned nr_pages, bool is_readahead);
+int f2fs_mpage_readpages(struct address_space *mapping, pgoff_t start,
+		struct page *page, unsigned nr_pages, bool is_readahead);
 struct page *f2fs_get_read_data_page(struct inode *inode, pgoff_t index,
 			int op_flags, bool for_write);
 struct page *f2fs_find_data_page(struct inode *inode, pgoff_t index);
diff --git a/fs/f2fs/verity.c b/fs/f2fs/verity.c
index d7d430a6f130..71e92b9b3aa6 100644
--- a/fs/f2fs/verity.c
+++ b/fs/f2fs/verity.c
@@ -231,7 +231,6 @@ static int f2fs_get_verity_descriptor(struct inode *inode, void *buf,
 static void f2fs_merkle_tree_readahead(struct address_space *mapping,
 				       pgoff_t start_index, unsigned long count)
 {
-	LIST_HEAD(pages);
 	unsigned int nr_pages = 0;
 	struct page *page;
 	pgoff_t index;
@@ -240,16 +239,23 @@ static void f2fs_merkle_tree_readahead(struct address_space *mapping,
 	for (index = start_index; index < start_index + count; index++) {
 		page = xa_load(&mapping->i_pages, index);
 		if (!page || xa_is_value(page)) {
-			page = __page_cache_alloc(readahead_gfp_mask(mapping));
+			gfp_t gfp = readahead_gfp_mask(mapping);
+			page = __page_cache_alloc(gfp);
 			if (!page)
 				break;
-			page->index = index;
-			list_add(&page->lru, &pages);
+			if (add_to_page_cache_lru(page, mapping, index, gfp)) {
+				put_page(page);
+				break;
+			}
 			nr_pages++;
 		}
 	}
+
+	if (!nr_pages)
+		return;
+
 	blk_start_plug(&plug);
-	f2fs_mpage_readpages(mapping, &pages, NULL, nr_pages, true);
+	f2fs_mpage_readpages(mapping, start_index, NULL, nr_pages, true);
 	blk_finish_plug(&plug);
 }
 
diff --git a/include/trace/events/f2fs.h b/include/trace/events/f2fs.h
index 67a97838c2a0..d72da4a33883 100644
--- a/include/trace/events/f2fs.h
+++ b/include/trace/events/f2fs.h
@@ -1375,9 +1375,9 @@ TRACE_EVENT(f2fs_writepages,
 
 TRACE_EVENT(f2fs_readpages,
 
-	TP_PROTO(struct inode *inode, struct page *page, unsigned int nrpage),
+	TP_PROTO(struct inode *inode, pgoff_t start, unsigned int nrpage),
 
-	TP_ARGS(inode, page, nrpage),
+	TP_ARGS(inode, start, nrpage),
 
 	TP_STRUCT__entry(
 		__field(dev_t,	dev)
@@ -1389,7 +1389,7 @@ TRACE_EVENT(f2fs_readpages,
 	TP_fast_assign(
 		__entry->dev	= inode->i_sb->s_dev;
 		__entry->ino	= inode->i_ino;
-		__entry->start	= page->index;
+		__entry->start	= start;
 		__entry->nrpage	= nrpage;
 	),
 
-- 
2.24.1

[PATCH v4 11/12] fuse: Convert from readpages to readahead

[Matthew Wilcox]

From: "Matthew Wilcox (Oracle)" <willy@infradead.org>

Use the new readahead operation in fuse.  Switching away from the
read_cache_pages() helper gets rid of an implicit call to put_page(),
so we can get rid of the get_page() call in fuse_readpages_fill().

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 fs/fuse/file.c | 37 +++++++++++++++++--------------------
 1 file changed, 17 insertions(+), 20 deletions(-)

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index ce715380143c..5460ff1bf155 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -911,9 +911,8 @@ struct fuse_fill_data {
 	unsigned int max_pages;
 };
 
-static int fuse_readpages_fill(void *_data, struct page *page)
+static int fuse_readpages_fill(struct fuse_fill_data *data, struct page *page)
 {
-	struct fuse_fill_data *data = _data;
 	struct fuse_io_args *ia = data->ia;
 	struct fuse_args_pages *ap = &ia->ap;
 	struct inode *inode = data->inode;
@@ -929,10 +928,8 @@ static int fuse_readpages_fill(void *_data, struct page *page)
 					fc->max_pages);
 		fuse_send_readpages(ia, data->file);
 		data->ia = ia = fuse_io_alloc(NULL, data->max_pages);
-		if (!ia) {
-			unlock_page(page);
+		if (!ia)
 			return -ENOMEM;
-		}
 		ap = &ia->ap;
 	}
 
@@ -942,7 +939,6 @@ static int fuse_readpages_fill(void *_data, struct page *page)
 		return -EIO;
 	}
 
-	get_page(page);
 	ap->pages[ap->num_pages] = page;
 	ap->descs[ap->num_pages].length = PAGE_SIZE;
 	ap->num_pages++;
@@ -950,15 +946,13 @@ static int fuse_readpages_fill(void *_data, struct page *page)
 	return 0;
 }
 
-static int fuse_readpages(struct file *file, struct address_space *mapping,
-			  struct list_head *pages, unsigned nr_pages)
+static unsigned fuse_readahead(struct file *file, struct address_space *mapping,
+			  pgoff_t start, unsigned nr_pages)
 {
 	struct inode *inode = mapping->host;
 	struct fuse_conn *fc = get_fuse_conn(inode);
 	struct fuse_fill_data data;
-	int err;
 
-	err = -EIO;
 	if (is_bad_inode(inode))
 		goto out;
 
@@ -966,21 +960,24 @@ static int fuse_readpages(struct file *file, struct address_space *mapping,
 	data.inode = inode;
 	data.nr_pages = nr_pages;
 	data.max_pages = min_t(unsigned int, nr_pages, fc->max_pages);
-;
 	data.ia = fuse_io_alloc(NULL, data.max_pages);
-	err = -ENOMEM;
 	if (!data.ia)
 		goto out;
 
-	err = read_cache_pages(mapping, pages, fuse_readpages_fill, &data);
-	if (!err) {
-		if (data.ia->ap.num_pages)
-			fuse_send_readpages(data.ia, file);
-		else
-			fuse_io_free(data.ia);
+	while (nr_pages) {
+		struct page *page = readahead_page(mapping, start++);
+
+		if (fuse_readpages_fill(&data, page) != 0)
+			goto out;
+		nr_pages--;
 	}
+
+	if (data.ia->ap.num_pages)
+		fuse_send_readpages(data.ia, file);
+	else
+		fuse_io_free(data.ia);
 out:
-	return err;
+	return nr_pages;
 }
 
 static ssize_t fuse_cache_read_iter(struct kiocb *iocb, struct iov_iter *to)
@@ -3358,10 +3355,10 @@ static const struct file_operations fuse_file_operations = {
 
 static const struct address_space_operations fuse_file_aops  = {
 	.readpage	= fuse_readpage,
+	.readahead	= fuse_readahead,
 	.writepage	= fuse_writepage,
 	.writepages	= fuse_writepages,
 	.launder_page	= fuse_launder_page,
-	.readpages	= fuse_readpages,
 	.set_page_dirty	= __set_page_dirty_nobuffers,
 	.bmap		= fuse_bmap,
 	.direct_IO	= fuse_direct_IO,
-- 
2.24.1

[PATCH v4 12/12] iomap: Convert from readpages to readahead

[Matthew Wilcox]

From: "Matthew Wilcox (Oracle)" <willy@infradead.org>

Use the new readahead operation in XFS and iomap.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: linux-xfs@vger.kernel.org
---
 fs/iomap/buffered-io.c | 72 +++++++++---------------------------------
 fs/iomap/trace.h       |  2 +-
 fs/xfs/xfs_aops.c      | 10 +++---
 include/linux/iomap.h  |  2 +-
 4 files changed, 22 insertions(+), 64 deletions(-)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index cb3511eb152a..490b66ea3298 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -216,7 +216,6 @@ struct iomap_readpage_ctx {
 	bool			cur_page_in_bio;
 	bool			is_readahead;
 	struct bio		*bio;
-	struct list_head	*pages;
 };
 
 static void
@@ -367,36 +366,8 @@ iomap_readpage(struct page *page, const struct iomap_ops *ops)
 }
 EXPORT_SYMBOL_GPL(iomap_readpage);
 
-static struct page *
-iomap_next_page(struct inode *inode, struct list_head *pages, loff_t pos,
-		loff_t length, loff_t *done)
-{
-	while (!list_empty(pages)) {
-		struct page *page = lru_to_page(pages);
-
-		if (page_offset(page) >= (u64)pos + length)
-			break;
-
-		list_del(&page->lru);
-		if (!add_to_page_cache_lru(page, inode->i_mapping, page->index,
-				GFP_NOFS))
-			return page;
-
-		/*
-		 * If we already have a page in the page cache at index we are
-		 * done.  Upper layers don't care if it is uptodate after the
-		 * readpages call itself as every page gets checked again once
-		 * actually needed.
-		 */
-		*done += PAGE_SIZE;
-		put_page(page);
-	}
-
-	return NULL;
-}
-
 static loff_t
-iomap_readpages_actor(struct inode *inode, loff_t pos, loff_t length,
+iomap_readahead_actor(struct inode *inode, loff_t pos, loff_t length,
 		void *data, struct iomap *iomap, struct iomap *srcmap)
 {
 	struct iomap_readpage_ctx *ctx = data;
@@ -410,10 +381,8 @@ iomap_readpages_actor(struct inode *inode, loff_t pos, loff_t length,
 			ctx->cur_page = NULL;
 		}
 		if (!ctx->cur_page) {
-			ctx->cur_page = iomap_next_page(inode, ctx->pages,
-					pos, length, &done);
-			if (!ctx->cur_page)
-				break;
+			ctx->cur_page = readahead_page(inode->i_mapping,
+					pos / PAGE_SIZE);
 			ctx->cur_page_in_bio = false;
 		}
 		ret = iomap_readpage_actor(inode, pos + done, length - done,
@@ -423,48 +392,37 @@ iomap_readpages_actor(struct inode *inode, loff_t pos, loff_t length,
 	return done;
 }
 
-int
-iomap_readpages(struct address_space *mapping, struct list_head *pages,
+unsigned
+iomap_readahead(struct address_space *mapping, pgoff_t start,
 		unsigned nr_pages, const struct iomap_ops *ops)
 {
 	struct iomap_readpage_ctx ctx = {
-		.pages		= pages,
 		.is_readahead	= true,
 	};
-	loff_t pos = page_offset(list_entry(pages->prev, struct page, lru));
-	loff_t last = page_offset(list_entry(pages->next, struct page, lru));
-	loff_t length = last - pos + PAGE_SIZE, ret = 0;
+	loff_t pos = start * PAGE_SIZE;
+	loff_t length = nr_pages * PAGE_SIZE;
 
-	trace_iomap_readpages(mapping->host, nr_pages);
+	trace_iomap_readahead(mapping->host, nr_pages);
 
 	while (length > 0) {
-		ret = iomap_apply(mapping->host, pos, length, 0, ops,
-				&ctx, iomap_readpages_actor);
+		loff_t ret = iomap_apply(mapping->host, pos, length, 0, ops,
+				&ctx, iomap_readahead_actor);
 		if (ret <= 0) {
 			WARN_ON_ONCE(ret == 0);
-			goto done;
+			break;
 		}
 		pos += ret;
 		length -= ret;
 	}
-	ret = 0;
-done:
+
 	if (ctx.bio)
 		submit_bio(ctx.bio);
-	if (ctx.cur_page) {
-		if (!ctx.cur_page_in_bio)
-			unlock_page(ctx.cur_page);
+	if (ctx.cur_page && ctx.cur_page_in_bio)
 		put_page(ctx.cur_page);
-	}
 
-	/*
-	 * Check that we didn't lose a page due to the arcance calling
-	 * conventions..
-	 */
-	WARN_ON_ONCE(!ret && !list_empty(ctx.pages));
-	return ret;
+	return length / PAGE_SIZE;
 }
-EXPORT_SYMBOL_GPL(iomap_readpages);
+EXPORT_SYMBOL_GPL(iomap_readahead);
 
 /*
  * iomap_is_partially_uptodate checks whether blocks within a page are
diff --git a/fs/iomap/trace.h b/fs/iomap/trace.h
index 6dc227b8c47e..d6ba705f938a 100644
--- a/fs/iomap/trace.h
+++ b/fs/iomap/trace.h
@@ -39,7 +39,7 @@ DEFINE_EVENT(iomap_readpage_class, name,	\
 	TP_PROTO(struct inode *inode, int nr_pages), \
 	TP_ARGS(inode, nr_pages))
 DEFINE_READPAGE_EVENT(iomap_readpage);
-DEFINE_READPAGE_EVENT(iomap_readpages);
+DEFINE_READPAGE_EVENT(iomap_readahead);
 
 DECLARE_EVENT_CLASS(iomap_page_class,
 	TP_PROTO(struct inode *inode, struct page *page, unsigned long off,
diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
index 3a688eb5c5ae..4d9da34e759b 100644
--- a/fs/xfs/xfs_aops.c
+++ b/fs/xfs/xfs_aops.c
@@ -621,14 +621,14 @@ xfs_vm_readpage(
 	return iomap_readpage(page, &xfs_read_iomap_ops);
 }
 
-STATIC int
-xfs_vm_readpages(
+STATIC unsigned
+xfs_vm_readahead(
 	struct file		*unused,
 	struct address_space	*mapping,
-	struct list_head	*pages,
+	pgoff_t			start,
 	unsigned		nr_pages)
 {
-	return iomap_readpages(mapping, pages, nr_pages, &xfs_read_iomap_ops);
+	return iomap_readahead(mapping, start, nr_pages, &xfs_read_iomap_ops);
 }
 
 static int
@@ -644,7 +644,7 @@ xfs_iomap_swapfile_activate(
 
 const struct address_space_operations xfs_address_space_operations = {
 	.readpage		= xfs_vm_readpage,
-	.readpages		= xfs_vm_readpages,
+	.readahead		= xfs_vm_readahead,
 	.writepage		= xfs_vm_writepage,
 	.writepages		= xfs_vm_writepages,
 	.set_page_dirty		= iomap_set_page_dirty,
diff --git a/include/linux/iomap.h b/include/linux/iomap.h
index 8b09463dae0d..81c6067e9b61 100644
--- a/include/linux/iomap.h
+++ b/include/linux/iomap.h
@@ -155,7 +155,7 @@ loff_t iomap_apply(struct inode *inode, loff_t pos, loff_t length,
 ssize_t iomap_file_buffered_write(struct kiocb *iocb, struct iov_iter *from,
 		const struct iomap_ops *ops);
 int iomap_readpage(struct page *page, const struct iomap_ops *ops);
-int iomap_readpages(struct address_space *mapping, struct list_head *pages,
+unsigned iomap_readahead(struct address_space *, pgoff_t start,
 		unsigned nr_pages, const struct iomap_ops *ops);
 int iomap_set_page_dirty(struct page *page);
 int iomap_is_partially_uptodate(struct page *page, unsigned long from,
-- 
2.24.1

Re: [PATCH v4 00/12] Change readahead API

[David Sterba]

On Sat, Feb 01, 2020 at 07:12:28AM -0800, Matthew Wilcox wrote:
> From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
> 
> I would particularly value feedback on this from the gfs2 and ocfs2
> maintainers.  They have non-trivial changes, and a review on patch 5
> would be greatly appreciated.
> 
> This series adds a readahead address_space operation to eventually
> replace the readpages operation.  The key difference is that
> pages are added to the page cache as they are allocated (and
> then looked up by the filesystem) instead of passing them on a
> list to the readpages operation and having the filesystem add
> them to the page cache.  It's a net reduction in code for each
> implementation, more efficient than walking a list, and solves
> the direct-write vs buffered-read problem reported by yu kuai at
> https://lore.kernel.org/linux-fsdevel/20200116063601.39201-1-yukuai3@huawei.com/
> 
> v4:
>  - Rebase on current Linus (a62aa6f7f50a ("Merge tag 'gfs2-for-5.6'"))

I've tried to test the patchset but haven't got very far, it crashes at boot
ritht after VFS mounts the root. The patches are from mailinglist, applied on
current master, bug I saw the same crash with the git branch in your
repo (probably v1).

(gdb) l *(ext4_mpage_readpages+0x1da/0xc20)
0xffffffff813753f0 is in ext4_mpage_readpages (fs/ext4/readpage.c:226).
221             return i_size_read(inode);
222     }
223
224     int ext4_mpage_readpages(struct address_space *mapping, pgoff_t start,
225                     struct page *page, unsigned nr_pages, bool is_readahead)
226     {
227             struct bio *bio = NULL;
228             sector_t last_block_in_bio = 0;
229
230             struct inode *inode = mapping->host;

[    8.008531] BUG: kernel NULL pointer dereference, address: 0000000000000000
[    8.011482] #PF: supervisor read access in kernel mode
[    8.014121] #PF: error_code(0x0000) - not-present page
[    8.016767] PGD 0 P4D 0
[    8.018352] Oops: 0000 [#1] SMP
[    8.019716] CPU: 2 PID: 1 Comm: swapper/0 Not tainted 5.5.0-default+ #955
[    8.021746] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.0-59-gc9ba527-rebuilt.opensuse.org 04/01/2014
[    8.025244] RIP: 0010:ext4_mpage_readpages+0x1da/0xc20
[    8.026817] Code: 7c 24 4e 00 0f 85 23 04 00 00 44 29 74 24 3c 83 6c 24 48 01 0f 84 4d 04 00 00 80 7c 24 4e 00 0f 85 fc 05 00 00 48 8b 4c 24 18 <48> 8b 01 f6 c4 20 75 89 4c 8b 69 20 b9 0c 00 00 00 2b 4c 24 38 83
[    8.031957] RSP: 0000:ffffb34f40013988 EFLAGS: 00010292
[    8.033691] RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
[    8.035533] RDX: 0000000000000001 RSI: ffffffff960934c0 RDI: ffffffff9681a080
[    8.036900] RBP: 0000000000000001 R08: ffffb34f40013a68 R09: 0000000000000000
[    8.038461] R10: 0000000000000038 R11: 0000000000000000 R12: 0000000000000004
[    8.040698] R13: ffff9668ba4e18e0 R14: 0000000000000001 R15: 0000000000000000
[    8.042805] FS:  0000000000000000(0000) GS:ffff9668bda00000(0000) knlGS:0000000000000000
[    8.045396] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[    8.047233] CR2: 0000000000000000 CR3: 000000002e011001 CR4: 0000000000160ee0
[    8.049337] Call Trace:
[    8.050435]  ? __lock_acquire+0xee0/0x1320
[    8.051833]  ? release_pages+0x310/0x380
[    8.053265]  ? mark_held_locks+0x50/0x80
[    8.054468]  ext4_readahead+0x3b/0x50
[    8.055877]  read_pages+0x65/0x1a0
[    8.057167]  ? put_pages_list+0x90/0x90
[    8.058689]  __do_page_cache_readahead+0x24b/0x2a0
[    8.060394]  generic_file_buffered_read+0x7cf/0x9f0
[    8.062137]  ? sched_clock+0x5/0x10
[    8.063451]  ? up_read+0x18/0x240
[    8.064774]  ? ext4_xattr_get+0x97/0x2c0
[    8.066178]  new_sync_read+0x111/0x1a0
[    8.067423]  vfs_read+0xc5/0x180
[    8.068572]  kernel_read+0x2c/0x40
[    8.069788]  prepare_binprm+0x171/0x1b0
[    8.071311]  load_script+0x1c1/0x250
[    8.072643]  search_binary_handler+0x5f/0x210
[    8.074135]  exec_binprm+0xd7/0x290
[    8.075463]  __do_execve_file.isra.0+0x570/0x800
[    8.077400]  ? rest_init+0x2f1/0x2f5
[    8.078979]  do_execve+0x21/0x30
[    8.080420]  kernel_init+0xa4/0x11b
[    8.081856]  ? rest_init+0x2f5/0x2f5
[    8.083173]  ret_from_fork+0x24/0x30
[    8.084695] Modules linked in:
[    8.086055] CR2: 0000000000000000
[    8.087572] ---[ end trace 0890c371a706b34a ]---
[    8.089417] RIP: 0010:ext4_mpage_readpages+0x1da/0xc20
[    8.116836] BUG: sleeping function called from invalid context at include/linux/percpu-rwsem.h:38
[    8.119626] in_atomic(): 0, irqs_disabled(): 1, non_block: 0, pid: 1, name: swapper/0
[    8.122392] INFO: lockdep is turned off.
[    8.123694] irq event stamp: 18341344
[    8.124735] hardirqs last  enabled at (18341343): [<ffffffff95230c42>] free_unref_page_list+0x232/0x270
[    8.127918] hardirqs last disabled at (18341344): [<ffffffff95002b4b>] trace_hardirqs_off_thunk+0x1a/0x1c
[    8.131145] softirqs last  enabled at (18341250): [<ffffffff95a00358>] __do_softirq+0x358/0x52b
[    8.143060] softirqs last disabled at (18341243): [<ffffffff9508ae3d>] irq_exit+0x9d/0xb0
[    8.145603] CPU: 2 PID: 1 Comm: swapper/0 Tainted: G      D           5.5.0-default+ #955
[    8.148474] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.0-59-gc9ba527-rebuilt.opensuse.org 04/01/2014
[    8.152440] Call Trace:
[    8.153747]  dump_stack+0x71/0xa0
[    8.155238]  ___might_sleep.cold+0xa6/0xf9
[    8.156903]  exit_signals+0x31/0x310
[    8.158431]  ? __do_execve_file.isra.0+0x570/0x800
[    8.160179]  do_exit+0xa8/0xd60
[    8.161632]  ? rest_init+0x2f1/0x2f5
[    8.163204]  rewind_stack_do_exit+0x17/0x20
[    8.164931] Kernel panic - not syncing: Attempted to kill init! exitcode=0x00000009
[    8.167575] Kernel Offset: 0x14000000 from 0xffffffff81000000 (relocation range: 0xffffffff80000000-0xffffffffbfffffff)

Re: [PATCH v4 00/12] Change readahead API

[Matthew Wilcox]

On Tue, Feb 04, 2020 at 04:32:27PM +0100, David Sterba wrote:
> On Sat, Feb 01, 2020 at 07:12:28AM -0800, Matthew Wilcox wrote:
> > From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
> > 
> > I would particularly value feedback on this from the gfs2 and ocfs2
> > maintainers.  They have non-trivial changes, and a review on patch 5
> > would be greatly appreciated.
> > 
> > This series adds a readahead address_space operation to eventually
> > replace the readpages operation.  The key difference is that
> > pages are added to the page cache as they are allocated (and
> > then looked up by the filesystem) instead of passing them on a
> > list to the readpages operation and having the filesystem add
> > them to the page cache.  It's a net reduction in code for each
> > implementation, more efficient than walking a list, and solves
> > the direct-write vs buffered-read problem reported by yu kuai at
> > https://lore.kernel.org/linux-fsdevel/20200116063601.39201-1-yukuai3@huawei.com/
> > 
> > v4:
> >  - Rebase on current Linus (a62aa6f7f50a ("Merge tag 'gfs2-for-5.6'"))
> 
> I've tried to test the patchset but haven't got very far, it crashes at boot
> ritht after VFS mounts the root. The patches are from mailinglist, applied on
> current master, bug I saw the same crash with the git branch in your
> repo (probably v1).

Yeah, I wasn't able to test at the time due to what turned out to be
the hpet bug in Linus' tree.  Now that's fixed, I've found & fixed a
couple more bugs.  There'll be a v5 once I fix the remaining problem
(looks like a missing page unlock somewhere).