linux-kernel - [ 203/218] mm: avoid swapping out with swappiness==0

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Message-Id: <20120928201524.875299290@linuxfoundation.org>
Date:	Fri, 28 Sep 2012 13:17:00 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	alan@...rguk.ukuu.org.uk, Satoru Moriya <satoru.moriya@....com>,
	Minchan Kim <minchan@...nel.org>,
	Rik van Riel <riel@...hat.com>,
	Jerome Marchand <jmarchan@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [ 203/218] mm: avoid swapping out with swappiness==0

3.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Satoru Moriya <satoru.moriya@....com>

commit fe35004fbf9eaf67482b074a2e032abb9c89b1dd upstream.

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@....com>
Acked-by: Minchan Kim <minchan@...nel.org>
Reviewed-by: Rik van Riel <riel@...hat.com>
Acked-by: Jerome Marchand <jmarchan@...hat.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 mm/vmscan.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1983,10 +1983,10 @@ static void get_scan_count(struct mem_cg
 	 * 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);
 
@@ -1999,7 +1999,7 @@ 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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