Commit fe35004f authored May 29, 2012 by Satoru Moriya Committed by Linus Torvalds May 29, 2012

mm: avoid swapping out with swappiness==0



Sometimes we'd like to avoid swapping out anonymous memory.  In
particular, avoid swapping out pages of important process or process
groups while there is a reasonable amount of pagecache on RAM so that we
can satisfy our customers' requirements.

OTOH, we can control how aggressive the kernel will swap memory pages with
/proc/sys/vm/swappiness for global and
/sys/fs/cgroup/memory/memory.swappiness for each memcg.

But with current reclaim implementation, the kernel may swap out even if
we set swappiness=0 and there is pagecache in RAM.

This patch changes the behavior with swappiness==0.  If we set
swappiness==0, the kernel does not swap out completely (for global reclaim
until the amount of free pages and filebacked pages in a zone has been
reduced to something very very small (nr_free + nr_filebacked < high
watermark)).

Signed-off-by: Satoru Moriya <satoru.moriya@hds.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Reviewed-by: Rik van Riel <riel@redhat.com>
Acked-by: Jerome Marchand <jmarchan@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent c50ac050

mm/vmscan.c

+3 −3

Original line number	Diff line number	Diff line
		@@ -1761,10 +1761,10 @@ static void get_scan_count(struct mem_cgroup_zone mz, struct scan_control sc,
		* proportional to the fraction of recently scanned pages on
		* each list that were recently referenced and in active use.
		*/
		ap = (anon_prio + 1) * (reclaim_stat->recent_scanned[0] + 1);
		ap = anon_prio * (reclaim_stat->recent_scanned[0] + 1);
		ap /= reclaim_stat->recent_rotated[0] + 1;

		fp = (file_prio + 1) * (reclaim_stat->recent_scanned[1] + 1);
		fp = file_prio * (reclaim_stat->recent_scanned[1] + 1);
		fp /= reclaim_stat->recent_rotated[1] + 1;
		spin_unlock_irq(&mz->zone->lru_lock);

		@@ -1777,7 +1777,7 @@ out:
		unsigned long scan;

		scan = zone_nr_lru_pages(mz, lru);
		if (priority \|\| noswap) {
		if (priority \|\| noswap \|\| !vmscan_swappiness(mz, sc)) {
		scan >>= priority;
		if (!scan && force_scan)
		scan = SWAP_CLUSTER_MAX;

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