linux-kernel - Re: [RFC 06/13] mm, thp: remove __GFP_NORETRY from khugepaged and madvised allocations

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Message-ID: <20160513120558.GL20141@dhcp22.suse.cz>
Date:	Fri, 13 May 2016 14:05:58 +0200
From:	Michal Hocko <mhocko@...nel.org>
To:	Vlastimil Babka <vbabka@...e.cz>
Cc:	linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Rik van Riel <riel@...hat.com>,
	David Rientjes <rientjes@...gle.com>,
	Mel Gorman <mgorman@...hsingularity.net>,
	Johannes Weiner <hannes@...xchg.org>,
	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [RFC 06/13] mm, thp: remove __GFP_NORETRY from khugepaged and
 madvised allocations

On Fri 13-05-16 10:23:31, Vlastimil Babka wrote:
> On 05/12/2016 06:20 PM, Michal Hocko wrote:
> > On Tue 10-05-16 09:35:56, Vlastimil Babka wrote:
> > [...]
> > > diff --git a/include/linux/gfp.h b/include/linux/gfp.h
> > > index 570383a41853..0cb09714d960 100644
> > > --- a/include/linux/gfp.h
> > > +++ b/include/linux/gfp.h
> > > @@ -256,8 +256,7 @@ struct vm_area_struct;
> > >   #define GFP_HIGHUSER	(GFP_USER | __GFP_HIGHMEM)
> > >   #define GFP_HIGHUSER_MOVABLE	(GFP_HIGHUSER | __GFP_MOVABLE)
> > >   #define GFP_TRANSHUGE	((GFP_HIGHUSER_MOVABLE | __GFP_COMP | \
> > > -			 __GFP_NOMEMALLOC | __GFP_NORETRY | __GFP_NOWARN) & \
> > > -			 ~__GFP_RECLAIM)
> > > +			 __GFP_NOMEMALLOC | __GFP_NOWARN) & ~__GFP_RECLAIM)
> > 
> > I am not sure this is the right thing to do. I think we should keep
> > __GFP_NORETRY and clear it where we want a stronger semantic. This is
> > just too suble that all callsites are doing the right thing.
> 
> That would complicate alloc_hugepage_direct_gfpmask() a bit, but if you
> think it's worth it, I can turn the default around, OK.

Hmm, on the other hand it is true that GFP_TRANSHUGE is clearing both
reclaim flags by default and then overwrites that. This is just too
ugly. Can we make GFP_TRANSHUGE to only define flags we care about and
then tweak those that should go away at the callsites which matter now
that we do not rely on is_thp_gfp_mask?

-- 
Michal Hocko
SUSE Labs