linux-kernel - Re: [PATCH 2/3] mm, oom: do not enfore OOM killer for __GFP

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Date:   Tue, 24 Jan 2017 13:40:49 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Hillf Danton <hillf.zj@...baba-inc.com>
Cc:     'Andrew Morton' <akpm@...ux-foundation.org>,
        'Johannes Weiner' <hannes@...xchg.org>,
        'Tetsuo Handa' <penguin-kernel@...ove.SAKURA.ne.jp>,
        'David Rientjes' <rientjes@...gle.com>,
        'Mel Gorman' <mgorman@...e.de>, linux-mm@...ck.org,
        'LKML' <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] mm, oom: do not enfore OOM killer for __GFP_NOFAIL
 automatically

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