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Subject[PATCH mmotm] vmscan: handle may_swap more strictly (Re: [PATCH mmotm] vmscan: fix may_swap handling for memcg)
> > and, too many recliaming pages is not only memcg issue. I don't think this
> > patch provide generic solution.
> >
> Ah, you're right. It's not only memcg issue.
>
How about this one ?

===
From: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>

Commit 2e2e425989080cc534fc0fca154cae515f971cf5 ("vmscan,memcg: reintroduce
sc->may_swap) add may_swap flag and handle it at get_scan_ratio().

But the result of get_scan_ratio() is ignored when priority == 0,
so anon lru is scanned even if may_swap == 0 or nr_swap_pages == 0.
IMHO, this is not an expected behavior.

As for memcg especially, because of this behavior many and many pages are
swapped-out just in vain when oom is invoked by mem+swap limit.

This patch is for handling may_swap flag more strictly.

Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
---
mm/vmscan.c | 18 +++++++++---------
1 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 2ddcfc8..bacb092 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1407,13 +1407,6 @@ static void get_scan_ratio(struct zone *zone, struct scan_control *sc,
unsigned long ap, fp;
struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc);

- /* If we have no swap space, do not bother scanning anon pages. */
- if (!sc->may_swap || (nr_swap_pages <= 0)) {
- percent[0] = 0;
- percent[1] = 100;
- return;
- }
-
anon = zone_nr_pages(zone, sc, LRU_ACTIVE_ANON) +
zone_nr_pages(zone, sc, LRU_INACTIVE_ANON);
file = zone_nr_pages(zone, sc, LRU_ACTIVE_FILE) +
@@ -1511,15 +1504,22 @@ static void shrink_zone(int priority, struct zone *zone,
enum lru_list l;
unsigned long nr_reclaimed = sc->nr_reclaimed;
unsigned long swap_cluster_max = sc->swap_cluster_max;
+ int noswap = 0;

- get_scan_ratio(zone, sc, percent);
+ /* If we have no swap space, do not bother scanning anon pages. */
+ if (!sc->may_swap || (nr_swap_pages <= 0)) {
+ noswap = 1;
+ percent[0] = 0;
+ percent[1] = 100;
+ } else
+ get_scan_ratio(zone, sc, percent);

for_each_evictable_lru(l) {
int file = is_file_lru(l);
unsigned long scan;

scan = zone_nr_pages(zone, sc, l);
- if (priority) {
+ if (priority || noswap) {
scan >>= priority;
scan = (scan * percent[file]) / 100;
}

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