On Thu 07-05-20 09:33:01, Shakeel Butt wrote:
> Currently the reclaim of excessive usage over memory.high is scheduled
> to run on returning to the userland. The main reason behind this
> approach was simplicity i.e. always reclaim with GFP_KERNEL context.
> However the underlying assumptions behind this approach are: the current
> task shares the memcg hierarchy with the given memcg and the memcg of
> the current task most probably will not change on return to userland.
>
> With the remote charging, the first assumption breaks and it allows the
> usage to grow way beyond the memory.high as the reclaim and the
> throttling becomes ineffective.
>
> This patch forces the synchronous reclaim and potentially throttling for
> the callers with context that allows blocking. For unblockable callers
> or whose synch high reclaim is still not successful, a high reclaim is
> scheduled either to return-to-userland if current task shares the
> hierarchy with the given memcg or to system work queue.
>
> Signed-off-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
I would just make the early break a bit more clear.
[...]
> @@ -2600,8 +2596,23 @@ static int try_charge(struct mem_cgroup *memcg, gfp_t gfp_mask,
> schedule_work(&memcg->high_work);
> break;
> }
> - current->memcg_nr_pages_over_high += batch;
> - set_notify_resume(current);
> +
> + if (gfpflags_allow_blocking(gfp_mask))
> + reclaim_over_high(memcg, gfp_mask, batch);
> +
/*
* reclaim_over_high reclaims parents up the
* hierarchy so we can break out early here.
*/
> + if (page_counter_read(&memcg->memory) <=
> + READ_ONCE(memcg->high))
> + break;
> + /*
> + * The above reclaim might not be able to do much. Punt
> + * the high reclaim to return to userland if the current
> + * task shares the hierarchy.
> + */
> + if (current->mm && mm_match_cgroup(current->mm, memcg)) {
> + current->memcg_nr_pages_over_high += batch;
> + set_notify_resume(current);
> + } else
> + schedule_work(&memcg->high_work);
> break;
> }
> } while ((memcg = parent_mem_cgroup(memcg)));
> --
> 2.26.2.526.g744177e7f7-goog
>
--
Michal Hocko
SUSE Labs
