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Date: Tue, 24 Jan 2017 13:40:49 +0100
From: Michal Hocko <mhocko@kernel.org>
To: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: "'Andrew Morton'" <akpm@linux-foundation.org>,
        "'Johannes Weiner'" <hannes@cmpxchg.org>,
        "'Tetsuo Handa'" <penguin-kernel@I-love.SAKURA.ne.jp>,
        "'David Rientjes'" <rientjes@google.com>,
        "'Mel Gorman'" <mgorman@suse.de>, linux-mm@kvack.org,
        "'LKML'" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 2/3] mm, oom: do not enfore OOM killer for __GFP_NOFAIL
 automatically
Message-ID: <20170124124048.GE6867@dhcp22.suse.cz>
References: <20161220134904.21023-1-mhocko@kernel.org>
 <20161220134904.21023-3-mhocko@kernel.org>
 <001f01d272f7$e53acbd0$afb06370$@alibaba-inc.com>
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On Fri 20-01-17 16:33:36, Hillf Danton wrote:
> 
> On Tuesday, December 20, 2016 9:49 PM Michal Hocko wrote: 
> > 
> > @@ -1013,7 +1013,7 @@ bool out_of_memory(struct oom_control *oc)
> >  	 * make sure exclude 0 mask - all other users should have at least
> >  	 * ___GFP_DIRECT_RECLAIM to get here.
> >  	 */
> > -	if (oc->gfp_mask && !(oc->gfp_mask & (__GFP_FS|__GFP_NOFAIL)))
> > +	if (oc->gfp_mask && !(oc->gfp_mask & __GFP_FS))
> >  		return true;
> > 
> As to GFP_NOFS|__GFP_NOFAIL request, can we check gfp mask
> one bit after another?
> 
> 	if (oc->gfp_mask) {
> 		if (!(oc->gfp_mask & __GFP_FS))
> 			return false;
> 
> 		/* No service for request that can handle fail result itself */
> 		if (!(oc->gfp_mask & __GFP_NOFAIL))
> 			return false;
> 	}

I really do not understand this request. This patch is removing the
__GFP_NOFAIL part... Besides that why should they return false?
-- 
Michal Hocko
SUSE Labs