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Subject: Re: __GFP_NOFAIL and oom_killer_disabled?
From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
References: <20150223102147.GB24272@dhcp22.suse.cz>
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	<20150225160223.GH26680@dhcp22.suse.cz>
In-Reply-To: <20150225160223.GH26680@dhcp22.suse.cz>
Message-Id: <201502260648.IBC35479.QMVHOtFOJSFFLO@I-love.SAKURA.ne.jp>
Date: Thu, 26 Feb 2015 06:48:02 +0900
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To: mhocko@suse.cz, hannes@cmpxchg.org
Cc: akpm@linux-foundation.org, tytso@mit.edu, david@fromorbit.com, dchinner@redhat.com, linux-mm@kvack.org, rientjes@google.com, oleg@redhat.com, mgorman@suse.de, torvalds@linux-foundation.org

Michal Hocko wrote:
> On Wed 25-02-15 20:22:22, Tetsuo Handa wrote:
> > Michal Hocko wrote:
> > > This commit hasn't introduced any behavior changes. GFP_NOFAIL
> > > allocations fail when OOM killer is disabled since beginning
> > > 7f33d49a2ed5 (mm, PM/Freezer: Disable OOM killer when tasks are frozen).
> > 
> > I thought that
> > 
> > -       out_of_memory(ac->zonelist, gfp_mask, order, ac->nodemask, false);
> > -       *did_some_progress = 1;
> > +       if (out_of_memory(ac->zonelist, gfp_mask, order, ac->nodemask, false))
> > +               *did_some_progress = 1;
> > 
> > in commit c32b3cbe0d067a9c "oom, PM: make OOM detection in the freezer
> > path raceless" introduced a code path which fails to set
> > *did_some_progress to non 0 value.
> 
> But this commit had also the following hunk:
> @@ -2317,9 +2315,6 @@ __alloc_pages_may_oom(gfp_t gfp_mask, unsigned int order,
>  
>         *did_some_progress = 0;
>  
> -       if (oom_killer_disabled)
> -               return NULL;
> -
> 
> so we even wouldn't get down to out_of_memory and returned with
> did_some_progress=0 right away. So the patch hasn't changed the logic.

OK.

> OK, that would change the bahavior for __GFP_NOFAIL|~__GFP_FS
> allocations. The patch from Johannes which reverts GFP_NOFS failure mode
> should go to stable and that should be sufficient IMO.
>  

mm-page_alloc-revert-inadvertent-__gfp_fs-retry-behavior-change.patch
fixes only ~__GFP_NOFAIL|~__GFP_FS case. I think we need David's version
http://marc.info/?l=linux-mm&m=142489687015873&w=2 for 3.19-stable .

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