[ 95/95] mm: avoid swapping out with swappiness==0

From: Ben Hutchings
Date: Sun Sep 09 2012 - 19:32:26 EST


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

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

From: Satoru Moriya <satoru.moriya@xxxxxxx>

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@xxxxxxx>
Acked-by: Minchan Kim <minchan@xxxxxxxxxx>
Reviewed-by: Rik van Riel <riel@xxxxxxxxxx>
Acked-by: Jerome Marchand <jmarchan@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
[bwh: Backported to 3.2:
- Adjust context
- vmscan_swappiness() does not have a zone parameter]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
mm/vmscan.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1977,10 +1977,10 @@ static void get_scan_count(struct zone *
* 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(&zone->lru_lock);

@@ -1993,7 +1993,7 @@ out:
unsigned long scan;

scan = zone_nr_lru_pages(zone, sc, l);
- if (priority || noswap) {
+ if (priority || noswap || !vmscan_swappiness(sc)) {
scan >>= priority;
if (!scan && force_scan)
scan = SWAP_CLUSTER_MAX;


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