On Wed 22-03-17 22:11:33, Yisheng Xie wrote:
> From: Yisheng Xie <xieyisheng1@xxxxxxxxxx>
>
> By reviewing code, I find that when enter do_try_to_free_pages, the
> may_thrash is always clear, and it will retry shrink zones to tap
> cgroup's reserves memory by setting may_thrash when the former
> shrink_zones reclaim nothing.
>
> However, when memcg is disabled or on legacy hierarchy, or there do not
> have any memcg protected by low limit, it should not do this useless
> retry at all, for we do not have any cgroup's reserves memory to tap,
> and we have already done hard work but made no progress, which as Michal
> pointed out in former version, we are trying hard to control the retry
> logical of page alloctor, and the current additional round of reclaim is
> just lame.
>
> Therefore, to avoid this unneeded retrying and make code more readable,
> we remove the may_thrash field in scan_control, instead, introduce
> memcg_low_reclaim and memcg_low_skipped, and only retry when
> memcg_low_skipped, by setting memcg_low_reclaim.
>
> Signed-off-by: Yisheng Xie <xieyisheng1@xxxxxxxxxx>
> Acked-by: Michal Hocko <mhocko@xxxxxxxx>
> Suggested-by: Johannes Weiner <hannes@xxxxxxxxxxx>
> Suggested-by: Michal Hocko <mhocko@xxxxxxxxxx>
> Suggested-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
> Reviewed-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
Yes, the naming is much better now. Btw. Acked-by tags should be usually
dropped after the patch is reworked. But I am OK with keeping it in this
particular case.
Thanks!
> ---
> v5:
> - remove may_thrash field in scan_control, and introduce mem_cgroup_reclaim
> and memcg_low_skipped to make code more readable. - Johannes
>
> v4:
> - add a new field in scan_control named memcg_low_protection to check whether
> there have any memcg protected by low limit. - Michal
>
> v3:
> - rename function may_thrash() to mem_cgroup_thrashed() to avoid confusing.
>
> v2:
> - more restrictive condition for retry of shrink_zones (restricting
> cgroup_disabled=memory boot option and cgroup legacy hierarchy) - Shakeel
>
> - add a stub function may_thrash() to avoid compile error or warning.
>
> - rename subject from "donot retry shrink zones when memcg is disable"
> to "more restrictive condition for retry in do_try_to_free_pages"
>
> Any comment is more than welcome!
>
> Hi, Andrew,
> Could you please help to drop the v4, thank you so much.
>
> Thanks
> Yisheng Xie
>
> mm/vmscan.c | 18 +++++++++++++-----
> 1 file changed, 13 insertions(+), 5 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index bc8031e..d214212 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -97,8 +97,13 @@ struct scan_control {
> /* Can pages be swapped as part of reclaim? */
> unsigned int may_swap:1;
>
> - /* Can cgroups be reclaimed below their normal consumption range? */
> - unsigned int may_thrash:1;
> + /*
> + * Cgroups are not reclaimed below their configured memory.low,
> + * unless we threaten to OOM. If any cgroups are skipped due to
> + * memory.low and nothing was reclaimed, go back for memory.low.
> + */
> + unsigned int memcg_low_reclaim:1;
> + unsigned int memcg_low_skipped:1;
>
> unsigned int hibernation_mode:1;
>
> @@ -2557,8 +2562,10 @@ static bool shrink_node(pg_data_t *pgdat, struct scan_control *sc)
> unsigned long scanned;
>
> if (mem_cgroup_low(root, memcg)) {
> - if (!sc->may_thrash)
> + if (!sc->memcg_low_reclaim) {
> + sc->memcg_low_skipped = 1;
> continue;
> + }
> mem_cgroup_events(memcg, MEMCG_LOW, 1);
> }
>
> @@ -2808,9 +2815,10 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
> return 1;
>
> /* Untapped cgroup reserves? Don't OOM, retry. */
> - if (!sc->may_thrash) {
> + if (sc->memcg_low_skipped) {
> sc->priority = initial_priority;
> - sc->may_thrash = 1;
> + sc->memcg_low_reclaim = 1;
> + sc->memcg_low_skipped = 0;
> goto retry;
> }
>
> --
> 1.9.1
>
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--
Michal Hocko
SUSE Labs
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