linux-kernel - Re: [PATCH] mm: memcontrol: fix missing wakeup oom task

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Date:   Fri, 5 Feb 2021 09:24:43 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     Muchun Song <songmuchun@...edance.com>
Cc:     hannes@...xchg.org, vdavydov.dev@...il.com,
        akpm@...ux-foundation.org, cgroups@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [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@...edance.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