[PATCH 1/2] iomap: don't mark the inode dirty in iomap_write_end

[PATCH 1/2] iomap: don't mark the inode dirty in iomap_write_end

[Andreas Gruenbacher]

Marking the inode dirty for each page copied into the page cache can be
very inefficient for file systems that use the VFS dirty inode tracking,
and is completely pointless for those that don't use the VFS dirty inode
tracking.  So instead, only set an iomap flag when changing the in-core
inode size, and open code the rest of __generic_write_end.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
---
 fs/gfs2/bmap.c        |  2 ++
 fs/iomap.c            | 15 ++++++++++++++-
 include/linux/iomap.h |  1 +
 3 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/fs/gfs2/bmap.c b/fs/gfs2/bmap.c
index 93ea1d529aa3..f4b895fc632d 100644
--- a/fs/gfs2/bmap.c
+++ b/fs/gfs2/bmap.c
@@ -1182,6 +1182,8 @@ static int gfs2_iomap_end(struct inode *inode, loff_t pos, loff_t length,
 
 	if (ip->i_qadata && ip->i_qadata->qa_qd_num)
 		gfs2_quota_unlock(ip);
+	if (iomap->flags & IOMAP_F_SIZE_CHANGED)
+		mark_inode_dirty(inode);
 	gfs2_write_unlock(inode);
 
 out:
diff --git a/fs/iomap.c b/fs/iomap.c
index 12654c2e78f8..97569064faaa 100644
--- a/fs/iomap.c
+++ b/fs/iomap.c
@@ -777,6 +777,7 @@ iomap_write_end(struct inode *inode, loff_t pos, unsigned len,
 		unsigned copied, struct page *page, struct iomap *iomap)
 {
 	const struct iomap_page_ops *page_ops = iomap->page_ops;
+	loff_t old_size = inode->i_size;
 	int ret;
 
 	if (iomap->type == IOMAP_INLINE) {
@@ -788,7 +789,19 @@ iomap_write_end(struct inode *inode, loff_t pos, unsigned len,
 		ret = __iomap_write_end(inode, pos, len, copied, page, iomap);
 	}
 
-	__generic_write_end(inode, pos, ret, page);
+	/*
+	 * Update the in-memory inode size after copying the data into the page
+	 * cache.  It's up to the file system to write the updated size to disk,
+	 * preferably after I/O completion so that no stale data is exposed.
+	 */
+	if (pos + ret > old_size) {
+		i_size_write(inode, pos + ret);
+		iomap->flags |= IOMAP_F_SIZE_CHANGED;
+	}
+	unlock_page(page);
+
+	if (old_size < pos)
+		pagecache_isize_extended(inode, old_size, pos);
 	if (page_ops && page_ops->page_done)
 		page_ops->page_done(inode, pos, copied, page, iomap);
 	put_page(page);
diff --git a/include/linux/iomap.h b/include/linux/iomap.h
index 2103b94cb1bf..1df9ea187a9a 100644
--- a/include/linux/iomap.h
+++ b/include/linux/iomap.h
@@ -35,6 +35,7 @@ struct vm_fault;
 #define IOMAP_F_NEW		0x01	/* blocks have been newly allocated */
 #define IOMAP_F_DIRTY		0x02	/* uncommitted metadata */
 #define IOMAP_F_BUFFER_HEAD	0x04	/* file system requires buffer heads */
+#define IOMAP_F_SIZE_CHANGED	0x08	/* file size has changed */
 
 /*
  * Flags that only need to be reported for IOMAP_REPORT requests:
-- 
2.20.1

[PATCH 2/2] fs: fold __generic_write_end back into generic_write_end

[Andreas Gruenbacher]

From: Christoph Hellwig <hch@lst.de>

This effectively reverts a6d639da63ae ("fs: factor out a
__generic_write_end helper") as we now open code what is left of that
helper in iomap.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 fs/buffer.c   | 62 ++++++++++++++++++++++++---------------------------
 fs/internal.h |  2 --
 2 files changed, 29 insertions(+), 35 deletions(-)

diff --git a/fs/buffer.c b/fs/buffer.c
index e450c55f6434..49a871570092 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -2086,38 +2086,6 @@ int block_write_begin(struct address_space *mapping, loff_t pos, unsigned len,
 }
 EXPORT_SYMBOL(block_write_begin);
 
-void __generic_write_end(struct inode *inode, loff_t pos, unsigned copied,
-		struct page *page)
-{
-	loff_t old_size = inode->i_size;
-	bool i_size_changed = false;
-
-	/*
-	 * No need to use i_size_read() here, the i_size cannot change under us
-	 * because we hold i_rwsem.
-	 *
-	 * But it's important to update i_size while still holding page lock:
-	 * page writeout could otherwise come in and zero beyond i_size.
-	 */
-	if (pos + copied > inode->i_size) {
-		i_size_write(inode, pos + copied);
-		i_size_changed = true;
-	}
-
-	unlock_page(page);
-
-	if (old_size < pos)
-		pagecache_isize_extended(inode, old_size, pos);
-	/*
-	 * Don't mark the inode dirty under page lock. First, it unnecessarily
-	 * makes the holding time of page lock longer. Second, it forces lock
-	 * ordering of page lock and transaction start for journaling
-	 * filesystems.
-	 */
-	if (i_size_changed)
-		mark_inode_dirty(inode);
-}
-
 int block_write_end(struct file *file, struct address_space *mapping,
 			loff_t pos, unsigned len, unsigned copied,
 			struct page *page, void *fsdata)
@@ -2158,9 +2126,37 @@ int generic_write_end(struct file *file, struct address_space *mapping,
 			loff_t pos, unsigned len, unsigned copied,
 			struct page *page, void *fsdata)
 {
+	struct inode *inode = mapping->host;
+	loff_t old_size = inode->i_size;
+	bool i_size_changed = false;
+
 	copied = block_write_end(file, mapping, pos, len, copied, page, fsdata);
-	__generic_write_end(mapping->host, pos, copied, page);
+
+	/*
+	 * No need to use i_size_read() here, the i_size cannot change under us
+	 * because we hold i_rwsem.
+	 *
+	 * But it's important to update i_size while still holding page lock:
+	 * page writeout could otherwise come in and zero beyond i_size.
+	 */
+	if (pos + copied > inode->i_size) {
+		i_size_write(inode, pos + copied);
+		i_size_changed = true;
+	}
+
+	unlock_page(page);
 	put_page(page);
+
+	if (old_size < pos)
+		pagecache_isize_extended(inode, old_size, pos);
+	/*
+	 * Don't mark the inode dirty under page lock. First, it unnecessarily
+	 * makes the holding time of page lock longer. Second, it forces lock
+	 * ordering of page lock and transaction start for journaling
+	 * filesystems.
+	 */
+	if (i_size_changed)
+		mark_inode_dirty(inode);
 	return copied;
 }
 EXPORT_SYMBOL(generic_write_end);
diff --git a/fs/internal.h b/fs/internal.h
index a48ef81be37d..2f3c3de51fad 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -40,8 +40,6 @@ static inline int __sync_blockdev(struct block_device *bdev, int wait)
 extern void guard_bio_eod(int rw, struct bio *bio);
 extern int __block_write_begin_int(struct page *page, loff_t pos, unsigned len,
 		get_block_t *get_block, struct iomap *iomap);
-void __generic_write_end(struct inode *inode, loff_t pos, unsigned copied,
-		struct page *page);
 
 /*
  * char_dev.c
-- 
2.20.1

Re: [PATCH 1/2] iomap: don't mark the inode dirty in iomap_write_end

[Christoph Hellwig]

On Wed, Jun 26, 2019 at 02:03:32PM +0200, Andreas Gruenbacher wrote:
> Marking the inode dirty for each page copied into the page cache can be
> very inefficient for file systems that use the VFS dirty inode tracking,
> and is completely pointless for those that don't use the VFS dirty inode
> tracking.  So instead, only set an iomap flag when changing the in-core
> inode size, and open code the rest of __generic_write_end.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>

Nitpick: a patch from you should never have me as the first signoff.
Just drop it, and if you feel fancy add a 'Partially based on code
from Christoph Hellwig.' sentence.  Not that I care much.

Otherwise looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>

Doesn't the series also need a third patch reducing the amount
of mark_inode_dirty calls as per your initial proposal?

Re: [PATCH 2/2] fs: fold __generic_write_end back into generic_write_end

[Christoph Hellwig]

On Wed, Jun 26, 2019 at 02:03:33PM +0200, Andreas Gruenbacher wrote:
> From: Christoph Hellwig <hch@lst.de>
> 
> This effectively reverts a6d639da63ae ("fs: factor out a
> __generic_write_end helper") as we now open code what is left of that
> helper in iomap.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

And this one needs an additional signoff from you as it went through
your hands..

Re: [PATCH 1/2] iomap: don't mark the inode dirty in iomap_write_end

[Andreas Gruenbacher]

On Wed, 26 Jun 2019 at 14:55, Christoph Hellwig <hch@lst.de> wrote:
> Doesn't the series also need a third patch reducing the amount
> of mark_inode_dirty calls as per your initial proposal?

The page dirtying already reduces from once per page to once per
mapping, so that should be good enough.

Thanks,
Andreas