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@xxxxxxxxxxxxxxx
> CC: Brian Foster <bfoster@xxxxxxxxxx>
> CC: Vlastimil Babka <vbabka@xxxxxxx>
> Reported-by: Petr Tůma <petr.tuma@xxxxxxxxxxxxxxx>
> Fixes: 99579ccec4e271c3d4d4e7c946058766812afdab
> Signed-off-by: Jan Kara <jack@xxxxxxx>
> ---
Reviewed-by: Brian Foster <bfoster@xxxxxxxxxx>
> 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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