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Subject[patch 2/2] vmscan: clip swap_cluster_max in shrink_all_memory()
shrink_inactive_list() scans in sc->swap_cluster_max chunks until it
hits the scan limit it was passed.

shrink_inactive_list()
{
do {
isolate_pages(swap_cluster_max)
shrink_page_list()
} while (nr_scanned < max_scan);
}

This assumes that swap_cluster_max is not bigger than the scan limit
because the latter is checked only after at least one iteration.

In shrink_all_memory() sc->swap_cluster_max is initialized to the
overall reclaim goal in the beginning but not decreased while reclaim
is making progress which leads to subsequent calls to
shrink_inactive_list() reclaiming way too much in the one iteration
that is done unconditionally.

Set sc->swap_cluster_max always to the proper goal before doing
shrink_all_zones()
shrink_list()
shrink_inactive_list().

While the current shrink_all_memory() happily reclaims more than
actually requested, this patch fixes it to never exceed the goal:

unpatched
wanted=10000 reclaimed=13356
wanted=10000 reclaimed=19711
wanted=10000 reclaimed=10289
wanted=10000 reclaimed=17306
wanted=10000 reclaimed=10700
wanted=10000 reclaimed=10004
wanted=10000 reclaimed=13301
wanted=10000 reclaimed=10976
wanted=10000 reclaimed=10605
wanted=10000 reclaimed=10088
wanted=10000 reclaimed=15000

patched
wanted=10000 reclaimed=10000
wanted=10000 reclaimed=9599
wanted=10000 reclaimed=8476
wanted=10000 reclaimed=8326
wanted=10000 reclaimed=10000
wanted=10000 reclaimed=10000
wanted=10000 reclaimed=9919
wanted=10000 reclaimed=10000
wanted=10000 reclaimed=10000
wanted=10000 reclaimed=10000
wanted=10000 reclaimed=10000
wanted=10000 reclaimed=9624
wanted=10000 reclaimed=10000
wanted=10000 reclaimed=10000
wanted=8500 reclaimed=8092
wanted=316 reclaimed=316

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: MinChan Kim <minchan.kim@gmail.com>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: Nigel Cunningham <ncunningham-lkml@crca.org.au>
Cc: Rik van Riel <riel@redhat.com>
---
mm/vmscan.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2105,7 +2105,6 @@ unsigned long shrink_all_memory(unsigned
struct scan_control sc = {
.gfp_mask = GFP_KERNEL,
.may_unmap = 0,
- .swap_cluster_max = nr_pages,
.may_writepage = 1,
.isolate_pages = isolate_pages_global,
};
@@ -2147,6 +2146,7 @@ unsigned long shrink_all_memory(unsigned
unsigned long nr_to_scan = nr_pages - sc.nr_reclaimed;

sc.nr_scanned = 0;
+ sc.swap_cluster_max = nr_to_scan;
shrink_all_zones(nr_to_scan, prio, pass, &sc);
if (sc.nr_reclaimed >= nr_pages)
goto out;



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