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SubjectRe: [PATCH mmotm] vmscan: handle may_swap more strictly (Re: [PATCH mmotm] vmscan: fix may_swap handling for memcg)
Date
> > > 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>

Looks great.
your patch doesn't only improve memcg, bug also improve noswap system.

Thanks.
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>



> ---
> 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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