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From: Dave Chinner <david@fromorbit.com>
To: linux-xfs@vger.kernel.org
Cc: linux-mm@kvack.org, linux-fsdevel@vger.kernel.org
Subject: [PATCH 15/26] mm: kswapd backoff for shrinkers
Date: Wed,  9 Oct 2019 14:21:13 +1100
Message-ID: <20191009032124.10541-16-david@fromorbit.com> (raw)
In-Reply-To: <20191009032124.10541-1-david@fromorbit.com>

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 fe8e8508f98d..c56a9ac6d042 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2951,8 +2951,16 @@ 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;
+			}
 		}
 
 		/*
-- 
2.23.0.rc1



  parent reply index

Thread overview: 87+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-09  3:20 [PATCH V2 00/26] mm, xfs: non-blocking inode reclaim Dave Chinner
2019-10-09  3:20 ` [PATCH 01/26] xfs: Lower CIL flush limit for large logs Dave Chinner
2019-10-11 12:39   ` Brian Foster
2019-10-30 17:08   ` Darrick J. Wong
2019-10-09  3:21 ` [PATCH 02/26] xfs: Throttle commits on delayed background CIL push Dave Chinner
2019-10-11 12:38   ` Brian Foster
2019-10-09  3:21 ` [PATCH 03/26] xfs: don't allow log IO to be throttled Dave Chinner
2019-10-11  9:35   ` Christoph Hellwig
2019-10-11 12:39   ` Brian Foster
2019-10-30 17:14   ` Darrick J. Wong
2019-10-09  3:21 ` [PATCH 04/26] xfs: Improve metadata buffer reclaim accountability Dave Chinner
2019-10-11 12:39   ` Brian Foster
2019-10-11 12:57     ` Christoph Hellwig
2019-10-11 23:14       ` Dave Chinner
2019-10-11 23:13     ` Dave Chinner
2019-10-12 12:05       ` Brian Foster
2019-10-13  3:14         ` Dave Chinner
2019-10-14 13:05           ` Brian Foster
2019-10-30 17:25   ` Darrick J. Wong
2019-10-30 21:43     ` Dave Chinner
2019-10-31  3:06       ` Darrick J. Wong
2019-10-31 20:50         ` Dave Chinner
2019-10-31 21:05           ` Darrick J. Wong
2019-10-31 21:22             ` Christoph Hellwig
2019-11-03 21:26             ` Dave Chinner
2019-11-04 23:08               ` Darrick J. Wong
2019-10-09  3:21 ` [PATCH 05/26] xfs: correctly acount for reclaimable slabs Dave Chinner
2019-10-11 12:39   ` Brian Foster
2019-10-30 17:16   ` Darrick J. Wong
2019-10-09  3:21 ` [PATCH 06/26] xfs: synchronous AIL pushing Dave Chinner
2019-10-11  9:42   ` Christoph Hellwig
2019-10-11 12:40   ` Brian Foster
2019-10-11 23:15     ` Dave Chinner
2019-10-09  3:21 ` [PATCH 07/26] xfs: tail updates only need to occur when LSN changes Dave Chinner
2019-10-11  9:50   ` Christoph Hellwig
2019-10-11 12:40   ` Brian Foster
2019-10-09  3:21 ` [PATCH 08/26] mm: directed shrinker work deferral Dave Chinner
2019-10-14  8:46   ` Christoph Hellwig
2019-10-14 13:06     ` Brian Foster
2019-10-18  7:59     ` Dave Chinner
2019-10-09  3:21 ` [PATCH 09/26] shrinkers: use defer_work for GFP_NOFS sensitive shrinkers Dave Chinner
2019-10-09  3:21 ` [PATCH 10/26] mm: factor shrinker work calculations Dave Chinner
2019-10-09  3:21 ` [PATCH 11/26] shrinker: defer work only to kswapd Dave Chinner
2019-10-09  3:21 ` [PATCH 12/26] shrinker: clean up variable types and tracepoints Dave Chinner
2019-10-09  3:21 ` [PATCH 13/26] mm: reclaim_state records pages reclaimed, not slabs Dave Chinner
2019-10-09  3:21 ` [PATCH 14/26] mm: back off direct reclaim on excessive shrinker deferral Dave Chinner
2019-10-11 16:21   ` Matthew Wilcox
2019-10-11 23:20     ` Dave Chinner
2019-10-09  3:21 ` Dave Chinner [this message]
2019-10-09  3:21 ` [PATCH 16/26] xfs: synchronous AIL pushing Dave Chinner
2019-10-11 10:18   ` Christoph Hellwig
2019-10-11 15:29     ` Brian Foster
2019-10-11 23:27       ` Dave Chinner
2019-10-12 12:08         ` Brian Foster
2019-10-09  3:21 ` [PATCH 17/26] xfs: don't block kswapd in inode reclaim Dave Chinner
2019-10-11 15:29   ` Brian Foster
2019-10-09  3:21 ` [PATCH 18/26] xfs: reduce kswapd blocking on inode locking Dave Chinner
2019-10-11 10:29   ` Christoph Hellwig
2019-10-09  3:21 ` [PATCH 19/26] xfs: kill background reclaim work Dave Chinner
2019-10-11 10:31   ` Christoph Hellwig
2019-10-09  3:21 ` [PATCH 20/26] xfs: use AIL pushing for inode reclaim IO Dave Chinner
2019-10-11 17:38   ` Brian Foster
2019-10-09  3:21 ` [PATCH 21/26] xfs: remove mode from xfs_reclaim_inodes() Dave Chinner
2019-10-11 10:39   ` Christoph Hellwig
2019-10-14 13:07   ` Brian Foster
2019-10-09  3:21 ` [PATCH 22/26] xfs: track reclaimable inodes using a LRU list Dave Chinner
2019-10-11 10:42   ` Christoph Hellwig
2019-10-14 13:07   ` Brian Foster
2019-10-09  3:21 ` [PATCH 23/26] xfs: reclaim inodes from the LRU Dave Chinner
2019-10-11 10:56   ` Christoph Hellwig
2019-10-30 23:25     ` Dave Chinner
2019-10-09  3:21 ` [PATCH 24/26] xfs: remove unusued old inode reclaim code Dave Chinner
2019-10-09  3:21 ` [PATCH 25/26] xfs: rework unreferenced inode lookups Dave Chinner
2019-10-11 12:55   ` Christoph Hellwig
2019-10-11 13:39     ` Peter Zijlstra
2019-10-11 23:38     ` Dave Chinner
2019-10-14 13:07   ` Brian Foster
2019-10-17  1:24     ` Dave Chinner
2019-10-17  7:57       ` Brian Foster
2019-10-18 20:29         ` Dave Chinner
2019-10-09  3:21 ` [PATCH 26/26] xfs: use xfs_ail_push_all_sync in xfs_reclaim_inodes Dave Chinner
2019-10-11  9:55   ` Christoph Hellwig
2019-10-09  7:06 ` [PATCH V2 00/26] mm, xfs: non-blocking inode reclaim Christoph Hellwig
2019-10-11 19:03 ` Josef Bacik
2019-10-11 23:48   ` Dave Chinner
2019-10-12  0:19     ` Josef Bacik
2019-10-12  0:48       ` Dave Chinner

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