linux-kernel - Re: [patch] mm, oom: remove gfp helper function

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Message-ID: <20141203155222.GH23236@dhcp22.suse.cz>
Date:	Wed, 3 Dec 2014 16:52:22 +0100
From:	Michal Hocko <mhocko@...e.cz>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	David Rientjes <rientjes@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Qiang Huang <h.huangqiang@...wei.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [patch] mm, oom: remove gfp helper function

On Mon 01-12-14 18:30:40, Johannes Weiner wrote:
> On Thu, Nov 27, 2014 at 11:25:47AM +0100, Michal Hocko wrote:
> > On Wed 26-11-14 14:17:32, David Rientjes wrote:
> > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > > --- a/mm/page_alloc.c
> > > +++ b/mm/page_alloc.c
> > > @@ -2706,7 +2706,7 @@ rebalance:
> > >  	 * running out of options and have to consider going OOM
> > >  	 */
> > >  	if (!did_some_progress) {
> > > -		if (oom_gfp_allowed(gfp_mask)) {
> > 		/*
> > 		 * Do not attempt to trigger OOM killer for !__GFP_FS
> > 		 * allocations because it would be premature to kill
> > 		 * anything just because the reclaim is stuck on
> > 		 * dirty/writeback pages.
> > 		 * __GFP_NORETRY allocations might fail and so the OOM
> > 		 * would be more harmful than useful.
> > 		 */
> 
> I don't think we need to explain the individual flags, but it would
> indeed be useful to remark here that we shouldn't OOM kill from
> allocations contexts with (severely) limited reclaim abilities.

Is __GFP_NORETRY really related to limited reclaim abilities? I thought
it was merely a way to tell the allocator to fail rather than spend too
much time reclaiming. If you are referring to __GFP_FS part then I have
no objections to be less specific, of course, but __GFP_IO would fall
into the same category but we are not checking for it. I have no idea
why we consider the first and not the later one, to be honest...

-- 
Michal Hocko
SUSE Labs
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