Re: [PATCH] xfs: Timely free truncated dirty pages

[Jan Kara <jack@suse.cz>]

On Tue 10-01-17 07:43:20, Brian Foster wrote:
> On Tue, Jan 10, 2017 at 11:17:45AM +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 is also confusing users thinking they are running out of
> > memory.
> > 
> > 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: 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>
> > ---
> 
> Ugh, so this is closer to the alternative I was considering at the time
> this was posted. Thanks for the fix. The code looks fine, I'd just like
> to update the comment...

OK, done.

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR