mm: vmscan: do not scale writeback pages when deciding whether to set ZONE_WRITEBACK (918fc718) · Commits · 戴 / test

After the patch "mm: vmscan: Flatten kswapd priority loop" was merged the scanning priority of kswapd changed. The priority now rises until it is scanning enough pages to meet the high watermark. shrink_inactive_list sets ZONE_WRITEBACK if a number of pages were encountered under writeback but this value is scaled based on the priority. As kswapd frequently scans with a higher priority now it is relatively easy to set ZONE_WRITEBACK. This patch removes the scaling and treates writeback pages similar to how it treats unqueued dirty pages and congested pages. The user-visible effect should be that kswapd will writeback fewer pages from reclaim context. Signed-off-by:

Mel Gorman <mgorman@suse.de> Cc: Rik van Riel <riel@redhat.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Michal Hocko <mhocko@suse.cz> Cc: Dave Chinner <david@fromorbit.com> Cc: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Signed-off-by:

Andrew Morton <akpm@linux-foundation.org> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

mm/vmscan.c

+1 −15

Original line number	Diff line number	Diff line
		@@ -1443,25 +1443,11 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
		* as there is no guarantee the dirtying process is throttled in the
		* same way balance_dirty_pages() manages.
		*
		* This scales the number of dirty pages that must be under writeback
		* before a zone gets flagged ZONE_WRITEBACK. It is a simple backoff
		* function that has the most effect in the range DEF_PRIORITY to
		* DEF_PRIORITY-2 which is the priority reclaim is considered to be
		* in trouble and reclaim is considered to be in trouble.
		*
		* DEF_PRIORITY 100% isolated pages must be PageWriteback to throttle
		* DEF_PRIORITY-1 50% must be PageWriteback
		* DEF_PRIORITY-2 25% must be PageWriteback, kswapd in trouble
		* ...
		* DEF_PRIORITY-6 For SWAP_CLUSTER_MAX isolated pages, throttle if any
		* isolated page is PageWriteback
		*
		* Once a zone is flagged ZONE_WRITEBACK, kswapd will count the number
		* of pages under pages flagged for immediate reclaim and stall if any
		* are encountered in the nr_immediate check below.
		*/
		if (nr_writeback && nr_writeback >=
		(nr_taken >> (DEF_PRIORITY - sc->priority)))
		if (nr_writeback && nr_writeback == nr_taken)
		zone_set_flag(zone, ZONE_WRITEBACK);

		/*

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