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

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Date:   Tue, 17 Apr 2018 20:08:24 -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.
> 
> [   17.072747] c0 0      <snip >: page allocation failure: order:0, mode:0x2200000(GFP_NOWAIT|__GFP_NOTRACK)
> 
> Let's not make user scared.
>  
> -	cw = kmalloc(sizeof(*cw), GFP_NOWAIT);
> +	cw = kmalloc(sizeof(*cw), GFP_NOWAIT | __GFP_NOWARN);
>  	if (!cw)

Not arguing against this patch.  But how many places do we want to use
GFP_NOWAIT without __GFP_NOWARN?  Not many, and the few which do do this
seem like they simply haven't added it yet.  Maybe this would be a good idea?

-#define GFP_NOWAIT      (__GFP_KSWAPD_RECLAIM)
+#define GFP_NOWAIT      (__GFP_KSWAPD_RECLAIM | __GFP_NOWARN)