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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 14/26] mm: back off direct reclaim on excessive shrinker deferral
Date: Wed,  9 Oct 2019 14:21:12 +1100
Message-ID: <20191009032124.10541-15-david@fromorbit.com> (raw)
In-Reply-To: <20191009032124.10541-1-david@fromorbit.com>

From: Dave Chinner <dchinner@redhat.com>

When the majority of possible shrinker reclaim work is deferred by
the shrinkers (e.g. due to GFP_NOFS context), and there is more work
defered than LRU pages were scanned, back off reclaim if there are
large amounts of IO in progress.

This tends to occur when there are inode cache heavy workloads that
have little page cache or application memory pressure on filesytems
like XFS. Inode cache heavy workloads involve lots of IO, so if we
are getting device congestion it is indicative of memory reclaim
running up against an IO throughput limitation. in this situation
we need to throttle direct reclaim as we nee dto wait for kswapd to
get some of the deferred work done.

However, if there is no device congestion, then the system is
keeping up with both the workload and memory reclaim and so there's
no need to throttle.

Hence we should only back off scanning for a bit if we see this
condition and there is block device congestion present.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
---
 include/linux/swap.h |  2 ++
 mm/vmscan.c          | 30 +++++++++++++++++++++++++++++-
 2 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/include/linux/swap.h b/include/linux/swap.h
index 72b855fe20b0..da0913e14bb9 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -131,6 +131,8 @@ union swap_header {
  */
 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 */
 };
 
 /*
diff --git a/mm/vmscan.c b/mm/vmscan.c
index feea179bcb67..fe8e8508f98d 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -569,6 +569,8 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
 		deferred_count = min(deferred_count, freeable_objects * 2);
 
 	}
+	if (current->reclaim_state)
+		current->reclaim_state->scanned_objects += scanned_objects;
 
 	/*
 	 * Avoid risking looping forever due to too large nr value:
@@ -584,8 +586,11 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
 	 * If the shrinker can't run (e.g. due to gfp_mask constraints), then
 	 * defer the work to a context that can scan the cache.
 	 */
-	if (shrinkctl->defer_work)
+	if (shrinkctl->defer_work) {
+		if (current->reclaim_state)
+			current->reclaim_state->deferred_objects += scan_count;
 		goto done;
+	}
 
 	/*
 	 * Normally, we should not scan less than batch_size objects in one
@@ -2873,7 +2878,30 @@ static bool shrink_node(pg_data_t *pgdat, struct scan_control *sc)
 
 		if (reclaim_state) {
 			sc->nr_reclaimed += reclaim_state->reclaimed_pages;
+
+			/*
+			 * If we are deferring more work than we are actually
+			 * doing in the shrinkers, and we are scanning more
+			 * objects than we are pages, the we have a large amount
+			 * of slab caches we are deferring work to kswapd for.
+			 * We better back off here for a while, otherwise
+			 * we risk priority windup, swap storms and OOM kills
+			 * once we empty the page lists but still can't make
+			 * progress on the shrinker memory.
+			 *
+			 * kswapd won't ever defer work as it's run under a
+			 * GFP_KERNEL context and can always do work.
+			 */
+			if ((reclaim_state->deferred_objects >
+					sc->nr_scanned - nr_scanned) &&
+			    (reclaim_state->deferred_objects >
+					reclaim_state->scanned_objects)) {
+				wait_iff_congested(BLK_RW_ASYNC, HZ/50);
+			}
+
 			reclaim_state->reclaimed_pages = 0;
+			reclaim_state->deferred_objects = 0;
+			reclaim_state->scanned_objects = 0;
 		}
 
 		/* Record the subtree's reclaim efficiency */
-- 
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 ` Dave Chinner [this message]
2019-10-11 16:21   ` [PATCH 14/26] mm: back off direct reclaim on excessive shrinker deferral Matthew Wilcox
2019-10-11 23:20     ` Dave Chinner
2019-10-09  3:21 ` [PATCH 15/26] mm: kswapd backoff for shrinkers Dave Chinner
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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