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SubjectRe: [PATCH] mm: memcontrol: fix missing wakeup oom task
On Fri 05-02-21 14:23:10, Muchun Song wrote:
> We call memcg_oom_recover() in the uncharge_batch() to wakeup OOM task
> when page uncharged, but for the slab pages, we do not do this when page
> uncharged.

How does the patch deal with this?

> When we drain per cpu stock, we also should do this.

Can we have anything the per-cpu stock while entering the OOM path. IIRC
we do drain all cpus before entering oom path.

> The memcg_oom_recover() is small, so make it inline.

Does this lead to any code generation improvements? I would expect
compiler to be clever enough to inline static functions if that pays
off. If yes make this a patch on its own.

> And the parameter
> of memcg cannot be NULL, so remove the check.

2bd9bb206b338 has introduced the check without any explanation
whatsoever. I indeed do not see any potential path to provide a NULL
memcg here. This is an internal function so the check is unnecessary
indeed. Please make it a patch on its own.

> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> ---
> mm/memcontrol.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 8c035846c7a4..8569f4dbea2a 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1925,7 +1925,7 @@ static int memcg_oom_wake_function(wait_queue_entry_t *wait,
> return autoremove_wake_function(wait, mode, sync, arg);
> }
>
> -static void memcg_oom_recover(struct mem_cgroup *memcg)
> +static inline void memcg_oom_recover(struct mem_cgroup *memcg)
> {
> /*
> * For the following lockless ->under_oom test, the only required
> @@ -1935,7 +1935,7 @@ static void memcg_oom_recover(struct mem_cgroup *memcg)
> * achieved by invoking mem_cgroup_mark_under_oom() before
> * triggering notification.
> */
> - if (memcg && memcg->under_oom)
> + if (memcg->under_oom)
> __wake_up(&memcg_oom_waitq, TASK_NORMAL, 0, memcg);
> }
>
> @@ -2313,6 +2313,7 @@ static void drain_stock(struct memcg_stock_pcp *stock)
> page_counter_uncharge(&old->memory, stock->nr_pages);
> if (do_memsw_account())
> page_counter_uncharge(&old->memsw, stock->nr_pages);
> + memcg_oom_recover(old);
> stock->nr_pages = 0;
> }
>
> --
> 2.11.0

--
Michal Hocko
SUSE Labs

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