[v2] xfs: Timely free truncated dirty pages
diff mbox

Message ID 20170111090019.16837-1-jack@suse.cz
State Accepted
Headers show

Commit Message

Jan Kara Jan. 11, 2017, 9 a.m. UTC
Commit 99579ccec4e2 "xfs: skip dirty pages in ->releasepage()" started
to skip dirty pages in xfs_vm_releasepage() which also has the effect
that if a dirty page is truncated, it does not get freed by
block_invalidatepage() and is lingering in LRU list waiting for reclaim.
So a simple loop like:

while true; do
	dd if=/dev/zero of=file bs=1M count=100
	rm file
done

will keep using more and more memory until we hit low watermarks and
start pagecache reclaim which will eventually reclaim also the truncate
pages. Keeping these truncated (and thus never usable) pages in memory
is just a waste of memory, is unnecessarily stressing page cache
reclaim, and reportedly also leads to anonymous mmap(2) returning ENOMEM
prematurely.

So instead of just skipping dirty pages in xfs_vm_releasepage(), return
to old behavior of skipping them only if they have delalloc or unwritten
buffers and fix the spurious warnings by warning only if the page is
clean.

CC: stable@vger.kernel.org
CC: Brian Foster <bfoster@redhat.com>
CC: Vlastimil Babka <vbabka@suse.cz>
Reported-by: Petr Tůma <petr.tuma@d3s.mff.cuni.cz>
Fixes: 99579ccec4e271c3d4d4e7c946058766812afdab
Signed-off-by: Jan Kara <jack@suse.cz>
---
 fs/xfs/xfs_aops.c | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

Comments

Brian Foster Jan. 11, 2017, 12:03 p.m. UTC | #1
On Wed, Jan 11, 2017 at 10:00:19AM +0100, Jan Kara wrote:
> Commit 99579ccec4e2 "xfs: skip dirty pages in ->releasepage()" started
> to skip dirty pages in xfs_vm_releasepage() which also has the effect
> that if a dirty page is truncated, it does not get freed by
> block_invalidatepage() and is lingering in LRU list waiting for reclaim.
> So a simple loop like:
> 
> while true; do
> 	dd if=/dev/zero of=file bs=1M count=100
> 	rm file
> done
> 
> will keep using more and more memory until we hit low watermarks and
> start pagecache reclaim which will eventually reclaim also the truncate
> pages. Keeping these truncated (and thus never usable) pages in memory
> is just a waste of memory, is unnecessarily stressing page cache
> reclaim, and reportedly also leads to anonymous mmap(2) returning ENOMEM
> prematurely.
> 
> So instead of just skipping dirty pages in xfs_vm_releasepage(), return
> to old behavior of skipping them only if they have delalloc or unwritten
> buffers and fix the spurious warnings by warning only if the page is
> clean.
> 
> CC: stable@vger.kernel.org
> CC: Brian Foster <bfoster@redhat.com>
> CC: Vlastimil Babka <vbabka@suse.cz>
> Reported-by: Petr Tůma <petr.tuma@d3s.mff.cuni.cz>
> Fixes: 99579ccec4e271c3d4d4e7c946058766812afdab
> Signed-off-by: Jan Kara <jack@suse.cz>
> ---

Reviewed-by: Brian Foster <bfoster@redhat.com>

>  fs/xfs/xfs_aops.c | 19 +++++++++++--------
>  1 file changed, 11 insertions(+), 8 deletions(-)
> 
> diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
> index 0f56fcd3a5d5..631e7c0e0a29 100644
> --- a/fs/xfs/xfs_aops.c
> +++ b/fs/xfs/xfs_aops.c
> @@ -1152,19 +1152,22 @@ xfs_vm_releasepage(
>  	 * block_invalidatepage() can send pages that are still marked dirty
>  	 * but otherwise have invalidated buffers.
>  	 *
> -	 * We've historically freed buffers on the latter. Instead, quietly
> -	 * filter out all dirty pages to avoid spurious buffer state warnings.
> -	 * This can likely be removed once shrink_active_list() is fixed.
> +	 * We want to release the latter to avoid unnecessary buildup of the
> +	 * LRU, skip the former and warn if we've left any lingering
> +	 * delalloc/unwritten buffers on clean pages. Skip pages with delalloc
> +	 * or unwritten buffers and warn if the page is not dirty. Otherwise
> +	 * try to release the buffers.
>  	 */
> -	if (PageDirty(page))
> -		return 0;
> -
>  	xfs_count_page_state(page, &delalloc, &unwritten);
>  
> -	if (WARN_ON_ONCE(delalloc))
> +	if (delalloc) {
> +		WARN_ON_ONCE(!PageDirty(page));
>  		return 0;
> -	if (WARN_ON_ONCE(unwritten))
> +	}
> +	if (unwritten) {
> +		WARN_ON_ONCE(!PageDirty(page));
>  		return 0;
> +	}
>  
>  	return try_to_free_buffers(page);
>  }
> -- 
> 2.10.2
> 
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Darrick J. Wong Jan. 11, 2017, 6:47 p.m. UTC | #2
On Wed, Jan 11, 2017 at 10:00:19AM +0100, Jan Kara wrote:
> Commit 99579ccec4e2 "xfs: skip dirty pages in ->releasepage()" started
> to skip dirty pages in xfs_vm_releasepage() which also has the effect
> that if a dirty page is truncated, it does not get freed by
> block_invalidatepage() and is lingering in LRU list waiting for reclaim.
> So a simple loop like:
> 
> while true; do
> 	dd if=/dev/zero of=file bs=1M count=100
> 	rm file
> done
> 
> will keep using more and more memory until we hit low watermarks and
> start pagecache reclaim which will eventually reclaim also the truncate
> pages. Keeping these truncated (and thus never usable) pages in memory
> is just a waste of memory, is unnecessarily stressing page cache
> reclaim, and reportedly also leads to anonymous mmap(2) returning ENOMEM
> prematurely.
> 
> So instead of just skipping dirty pages in xfs_vm_releasepage(), return
> to old behavior of skipping them only if they have delalloc or unwritten
> buffers and fix the spurious warnings by warning only if the page is
> clean.
> 
> CC: stable@vger.kernel.org
> CC: Brian Foster <bfoster@redhat.com>
> CC: Vlastimil Babka <vbabka@suse.cz>
> Reported-by: Petr Tůma <petr.tuma@d3s.mff.cuni.cz>
> Fixes: 99579ccec4e271c3d4d4e7c946058766812afdab
> Signed-off-by: Jan Kara <jack@suse.cz>

Applied, thanks.

--D

> ---
>  fs/xfs/xfs_aops.c | 19 +++++++++++--------
>  1 file changed, 11 insertions(+), 8 deletions(-)
> 
> diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
> index 0f56fcd3a5d5..631e7c0e0a29 100644
> --- a/fs/xfs/xfs_aops.c
> +++ b/fs/xfs/xfs_aops.c
> @@ -1152,19 +1152,22 @@ xfs_vm_releasepage(
>  	 * block_invalidatepage() can send pages that are still marked dirty
>  	 * but otherwise have invalidated buffers.
>  	 *
> -	 * We've historically freed buffers on the latter. Instead, quietly
> -	 * filter out all dirty pages to avoid spurious buffer state warnings.
> -	 * This can likely be removed once shrink_active_list() is fixed.
> +	 * We want to release the latter to avoid unnecessary buildup of the
> +	 * LRU, skip the former and warn if we've left any lingering
> +	 * delalloc/unwritten buffers on clean pages. Skip pages with delalloc
> +	 * or unwritten buffers and warn if the page is not dirty. Otherwise
> +	 * try to release the buffers.
>  	 */
> -	if (PageDirty(page))
> -		return 0;
> -
>  	xfs_count_page_state(page, &delalloc, &unwritten);
>  
> -	if (WARN_ON_ONCE(delalloc))
> +	if (delalloc) {
> +		WARN_ON_ONCE(!PageDirty(page));
>  		return 0;
> -	if (WARN_ON_ONCE(unwritten))
> +	}
> +	if (unwritten) {
> +		WARN_ON_ONCE(!PageDirty(page));
>  		return 0;
> +	}
>  
>  	return try_to_free_buffers(page);
>  }
> -- 
> 2.10.2
> 
> --
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Patch
diff mbox

diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
index 0f56fcd3a5d5..631e7c0e0a29 100644
--- a/fs/xfs/xfs_aops.c
+++ b/fs/xfs/xfs_aops.c
@@ -1152,19 +1152,22 @@  xfs_vm_releasepage(
 	 * block_invalidatepage() can send pages that are still marked dirty
 	 * but otherwise have invalidated buffers.
 	 *
-	 * We've historically freed buffers on the latter. Instead, quietly
-	 * filter out all dirty pages to avoid spurious buffer state warnings.
-	 * This can likely be removed once shrink_active_list() is fixed.
+	 * We want to release the latter to avoid unnecessary buildup of the
+	 * LRU, skip the former and warn if we've left any lingering
+	 * delalloc/unwritten buffers on clean pages. Skip pages with delalloc
+	 * or unwritten buffers and warn if the page is not dirty. Otherwise
+	 * try to release the buffers.
 	 */
-	if (PageDirty(page))
-		return 0;
-
 	xfs_count_page_state(page, &delalloc, &unwritten);
 
-	if (WARN_ON_ONCE(delalloc))
+	if (delalloc) {
+		WARN_ON_ONCE(!PageDirty(page));
 		return 0;
-	if (WARN_ON_ONCE(unwritten))
+	}
+	if (unwritten) {
+		WARN_ON_ONCE(!PageDirty(page));
 		return 0;
+	}
 
 	return try_to_free_buffers(page);
 }