linux-kernel - Re: [PATCH -v2] mm, oom: do not fail __GFP_NOFAIL allocation if oom killer is disbaled

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Message-ID: <20150226173445.GG14878@dhcp22.suse.cz>
Date:	Thu, 26 Feb 2015 18:34:45 +0100
From:	Michal Hocko <mhocko@...e.cz>
To:	David Rientjes <rientjes@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Johannes Weiner <hannes@...xchg.org>,
	"\\\"Rafael J. Wysocki\\\"" <rjw@...ysocki.net>,
	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
	linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -v2] mm, oom: do not fail __GFP_NOFAIL allocation if oom
 killer is disbaled

On Wed 25-02-15 12:41:07, David Rientjes wrote:
> On Wed, 25 Feb 2015, Michal Hocko wrote:
> 
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index 2d224bbdf8e8..c2ff40a30003 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -2363,7 +2363,8 @@ __alloc_pages_may_oom(gfp_t gfp_mask, unsigned int order,
> >  			goto out;
> >  	}
> >  	/* Exhausted what can be done so it's blamo time */
> > -	if (out_of_memory(ac->zonelist, gfp_mask, order, ac->nodemask, false))
> > +	if (out_of_memory(ac->zonelist, gfp_mask, order, ac->nodemask, false)
> > +			|| WARN_ON_ONCE(gfp_mask & __GFP_NOFAIL))
> >  		*did_some_progress = 1;
> >  out:
> >  	oom_zonelist_unlock(ac->zonelist, gfp_mask);
> 
> Eek, not sure we actually need to play any games with did_some_progress, 
> it might be clearer just to do this

We would loose the warning which _might_ be helpful and I also find this
place better because it is close to the out_of_memory and this one has
only one failure mode. So I would prefer to stick with this unless there
are big objections.

> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2760,7 +2760,7 @@ retry:
>  							&did_some_progress);
>  			if (page)
>  				goto got_pg;
> -			if (!did_some_progress)
> +			if (!did_some_progress && !(gfp_mask & __GFP_NOFAIL))
>  				goto nopage;
>  		}
>  		/* Wait for some write requests to complete then retry */
> 
> Either way you decide, feel free to add my
> 
> Acked-by: David Rientjes <rientjes@...ogle.com>

Thanks!

Andrew, should I repost or you can pick it up from this thread? Assuming
you and others do not have objections of course.

-- 
Michal Hocko
SUSE Labs
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