+ mm-avoid-swapping-out-with-swappiness==0.patch added to -mm tree

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The patch titled
     Subject: mm: avoid swapping out with swappiness==0
has been added to the -mm tree.  Its filename is
     mm-avoid-swapping-out-with-swappiness==0.patch

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------------------------------------------------------
From: Satoru Moriya <satoru.moriya@xxxxxxx>
Subject: 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@xxxxxxx>
Acked-by: Minchan Kim <minchan@xxxxxxxxxx>
Reviewed-by: Rik van Riel <riel@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

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

diff -puN mm/vmscan.c~mm-avoid-swapping-out-with-swappiness==0 mm/vmscan.c
--- a/mm/vmscan.c~mm-avoid-swapping-out-with-swappiness==0
+++ a/mm/vmscan.c
@@ -1761,10 +1761,10 @@ 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);
 
@@ -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;
_
Subject: Subject: mm: avoid swapping out with swappiness==0

Patches currently in -mm which might be from satoru.moriya@xxxxxxx are

linux-next.patch
mm-avoid-swapping-out-with-swappiness==0.patch

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