linux-kernel - Re: [PATCH] mm:memcg: add __GFP_NOWARN in __memcg_schedule_kmem_cache

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Message-ID: <20180418133139.GB27475@bombadil.infradead.org>
Date:   Wed, 18 Apr 2018 06:31:39 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Minchan Kim <minchan@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>
Subject: Re: [PATCH] mm:memcg: add __GFP_NOWARN in
 __memcg_schedule_kmem_cache_create

On Wed, Apr 18, 2018 at 11:29:12AM +0900, Minchan Kim wrote:
> If there are heavy memory pressure, page allocation with __GFP_NOWAIT
> fails easily although it's order-0 request.
> I got below warning 9 times for normal boot.
> 
> Let's not make user scared.

Actually, can you explain why it's OK if this fails?  As I understand this
code, we'll fail to create a kmalloc cache for this memcg.  What problems
does that cause?

> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 448db08d97a0..671d07e73a3b 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -2200,7 +2200,7 @@ static void __memcg_schedule_kmem_cache_create(struct mem_cgroup *memcg,
>  {
>  	struct memcg_kmem_cache_create_work *cw;
>  
> -	cw = kmalloc(sizeof(*cw), GFP_NOWAIT);
> +	cw = kmalloc(sizeof(*cw), GFP_NOWAIT | __GFP_NOWARN);
>  	if (!cw)
>  		return;
>  
> -- 
> 2.17.0.484.g0c8726318c-goog
>