From: Brian Foster <bfoster@redhat.com>
To: Dave Chinner <david@fromorbit.com>
Cc: linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 16/28] mm: kswapd backoff for shrinkers
Date: Mon, 4 Nov 2019 14:58:53 -0500 [thread overview]
Message-ID: <20191104195853.GG10665@bfoster> (raw)
In-Reply-To: <20191031234618.15403-17-david@fromorbit.com>
On Fri, Nov 01, 2019 at 10:46:06AM +1100, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
>
> When kswapd reaches the end of the page LRU and starts hitting dirty
> pages, the logic in shrink_node() allows it to back off and wait for
> IO to complete, thereby preventing kswapd from scanning excessively
> and driving the system into swap thrashing and OOM conditions.
>
> When we have inode cache heavy workloads on XFS, we have exactly the
> same problem with reclaim inodes. The non-blocking kswapd reclaim
> will keep putting pressure onto the inode cache which is unable to
> make progress. When the system gets to the point where there is no
> pages in the LRU to free, there is no swap left and there are no
> clean inodes that can be freed, it will OOM. This has a specific
> signature in OOM:
>
> [ 110.841987] Mem-Info:
> [ 110.842816] active_anon:241 inactive_anon:82 isolated_anon:1
> active_file:168 inactive_file:143 isolated_file:0
> unevictable:2621523 dirty:1 writeback:8 unstable:0
> slab_reclaimable:564445 slab_unreclaimable:420046
> mapped:1042 shmem:11 pagetables:6509 bounce:0
> free:77626 free_pcp:2 free_cma:0
>
> In this case, we have about 500-600 pages left in teh LRUs, but we
> have ~565000 reclaimable slab pages still available for reclaim.
> Unfortunately, they are mostly dirty inodes, and so we really need
> to be able to throttle kswapd when shrinker progress is limited due
> to reaching the dirty end of the LRU...
>
> So, add a flag into the reclaim_state so if the shrinker decides it
> needs kswapd to back off and wait for a while (for whatever reason)
> it can do so.
>
> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> ---
> include/linux/swap.h | 1 +
> mm/vmscan.c | 10 +++++++++-
> 2 files changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> index da0913e14bb9..76fc28f0e483 100644
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -133,6 +133,7 @@ struct reclaim_state {
> unsigned long reclaimed_pages; /* pages freed by shrinkers */
> unsigned long scanned_objects; /* quantity of work done */
> unsigned long deferred_objects; /* work that wasn't done */
> + bool need_backoff; /* tell kswapd to slow down */
> };
>
> /*
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 13c11e10c9c5..0f7d35820057 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2949,8 +2949,16 @@ static bool shrink_node(pg_data_t *pgdat, struct scan_control *sc)
> * implies that pages are cycling through the LRU
> * faster than they are written so also forcibly stall.
> */
> - if (sc->nr.immediate)
> + if (sc->nr.immediate) {
> congestion_wait(BLK_RW_ASYNC, HZ/10);
> + } else if (reclaim_state && reclaim_state->need_backoff) {
> + /*
> + * Ditto, but it's a slab cache that is cycling
> + * through the LRU faster than they are written
> + */
> + congestion_wait(BLK_RW_ASYNC, HZ/10);
> + reclaim_state->need_backoff = false;
> + }
Seems reasonable from a functional standpoint, but why not plug in to
the existing stall instead of duplicate it? E.g., add a corresponding
->nr_immediate field to reclaim_state rather than a bool, then transfer
that to the scan_control earlier in the function where we already check
for reclaim_state and handle transferring fields (or alternatively just
leave the bool and use it to bump the scan_control field). That seems a
bit more consistent with the page processing code, keeps the
reclaim_state resets in one place and also wouldn't leave us with an
if/else here for the same stall. Hm?
Brian
> }
>
> /*
> --
> 2.24.0.rc0
>
next prev parent reply other threads:[~2019-11-04 19:59 UTC|newest]
Thread overview: 72+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-31 23:45 [PATCH 00/28] mm, xfs: non-blocking inode reclaim Dave Chinner
2019-10-31 23:45 ` [PATCH 01/28] xfs: Lower CIL flush limit for large logs Dave Chinner
2019-10-31 23:45 ` [PATCH 02/28] xfs: Throttle commits on delayed background CIL push Dave Chinner
2019-11-01 12:04 ` Brian Foster
2019-11-01 21:40 ` Dave Chinner
2019-11-04 22:48 ` Darrick J. Wong
2019-10-31 23:45 ` [PATCH 03/28] xfs: don't allow log IO to be throttled Dave Chinner
2019-10-31 23:45 ` [PATCH 04/28] xfs: Improve metadata buffer reclaim accountability Dave Chinner
2019-11-01 12:05 ` Brian Foster
2019-11-04 23:21 ` Darrick J. Wong
2019-10-31 23:45 ` [PATCH 05/28] xfs: correctly acount for reclaimable slabs Dave Chinner
2019-10-31 23:45 ` [PATCH 06/28] xfs: factor common AIL item deletion code Dave Chinner
2019-11-04 23:16 ` Darrick J. Wong
2019-10-31 23:45 ` [PATCH 07/28] xfs: tail updates only need to occur when LSN changes Dave Chinner
2019-11-04 23:18 ` Darrick J. Wong
2019-10-31 23:45 ` [PATCH 08/28] xfs: factor inode lookup from xfs_ifree_cluster Dave Chinner
2019-11-01 12:05 ` Brian Foster
2019-11-04 23:20 ` Darrick J. Wong
2019-10-31 23:45 ` [PATCH 09/28] mm: directed shrinker work deferral Dave Chinner
2019-11-04 15:25 ` Brian Foster
2019-11-14 20:49 ` Dave Chinner
2019-11-15 17:21 ` Brian Foster
2019-11-18 0:49 ` Dave Chinner
2019-11-19 15:12 ` Brian Foster
2019-10-31 23:46 ` [PATCH 10/28] shrinkers: use defer_work for GFP_NOFS sensitive shrinkers Dave Chinner
2019-10-31 23:46 ` [PATCH 11/28] mm: factor shrinker work calculations Dave Chinner
2019-11-02 10:55 ` kbuild test robot
2019-11-04 15:29 ` Brian Foster
2019-11-14 20:59 ` Dave Chinner
2019-10-31 23:46 ` [PATCH 12/28] shrinker: defer work only to kswapd Dave Chinner
2019-11-04 15:29 ` Brian Foster
2019-11-14 21:11 ` Dave Chinner
2019-11-15 17:23 ` Brian Foster
2019-10-31 23:46 ` [PATCH 13/28] shrinker: clean up variable types and tracepoints Dave Chinner
2019-11-04 15:30 ` Brian Foster
2019-10-31 23:46 ` [PATCH 14/28] mm: reclaim_state records pages reclaimed, not slabs Dave Chinner
2019-11-04 19:58 ` Brian Foster
2019-10-31 23:46 ` [PATCH 15/28] mm: back off direct reclaim on excessive shrinker deferral Dave Chinner
2019-11-04 19:58 ` Brian Foster
2019-11-14 21:28 ` Dave Chinner
2019-10-31 23:46 ` [PATCH 16/28] mm: kswapd backoff for shrinkers Dave Chinner
2019-11-04 19:58 ` Brian Foster [this message]
2019-11-14 21:41 ` Dave Chinner
2019-10-31 23:46 ` [PATCH 17/28] xfs: synchronous AIL pushing Dave Chinner
2019-11-05 17:05 ` Brian Foster
2019-10-31 23:46 ` [PATCH 18/28] xfs: don't block kswapd in inode reclaim Dave Chinner
2019-10-31 23:46 ` [PATCH 19/28] xfs: reduce kswapd blocking on inode locking Dave Chinner
2019-11-05 17:05 ` Brian Foster
2019-10-31 23:46 ` [PATCH 20/28] xfs: kill background reclaim work Dave Chinner
2019-11-05 17:05 ` Brian Foster
2019-10-31 23:46 ` [PATCH 21/28] xfs: use AIL pushing for inode reclaim IO Dave Chinner
2019-11-05 17:06 ` Brian Foster
2019-10-31 23:46 ` [PATCH 22/28] xfs: remove mode from xfs_reclaim_inodes() Dave Chinner
2019-10-31 23:46 ` [PATCH 23/28] xfs: track reclaimable inodes using a LRU list Dave Chinner
2019-10-31 23:46 ` [PATCH 24/28] xfs: reclaim inodes from the LRU Dave Chinner
2019-11-06 17:21 ` Brian Foster
2019-11-14 21:51 ` Dave Chinner
2019-10-31 23:46 ` [PATCH 25/28] xfs: remove unusued old inode reclaim code Dave Chinner
2019-11-06 17:21 ` Brian Foster
2019-10-31 23:46 ` [PATCH 26/28] xfs: use xfs_ail_push_all in xfs_reclaim_inodes Dave Chinner
2019-11-06 17:22 ` Brian Foster
2019-11-14 21:53 ` Dave Chinner
2019-10-31 23:46 ` [PATCH 27/28] rwsem: introduce down/up_write_non_owner Dave Chinner
2019-10-31 23:46 ` [PATCH 28/28] xfs: rework unreferenced inode lookups Dave Chinner
2019-11-06 22:18 ` Brian Foster
2019-11-14 22:16 ` Dave Chinner
2019-11-15 13:13 ` Christoph Hellwig
2019-11-15 17:26 ` Brian Foster
2019-11-18 1:00 ` Dave Chinner
2019-11-19 15:13 ` Brian Foster
2019-11-19 21:18 ` Dave Chinner
2019-11-20 12:42 ` Brian Foster
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