linux-kernel - Re: [PATCH] mm: avoid livelock on !__GFP

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Message-ID: <alpine.DEB.2.00.1110252347330.20273@chino.kir.corp.google.com>
Date:	Tue, 25 Oct 2011 23:51:45 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Colin Cross <ccross@...roid.com>
cc:	Mel Gorman <mgorman@...e.de>, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Andrea Arcangeli <aarcange@...hat.com>, linux-mm@...ck.org
Subject: Re: [PATCH] mm: avoid livelock on !__GFP_FS allocations

On Tue, 25 Oct 2011, Colin Cross wrote:

> >> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> >> index fef8dc3..59cd4ff 100644
> >> --- a/mm/page_alloc.c
> >> +++ b/mm/page_alloc.c
> >> @@ -1786,6 +1786,13 @@ should_alloc_retry(gfp_t gfp_mask, unsigned int order,
> >>                 return 0;
> >>
> >>         /*
> >> +        * If PM has disabled I/O, OOM is disabled and reclaim is unlikely
> >> +        * to make any progress.  To prevent a livelock, don't retry.
> >> +        */
> >> +       if (!(gfp_allowed_mask & __GFP_FS))
> >> +               return 0;
> >> +
> >> +       /*
> >>          * In this implementation, order <= PAGE_ALLOC_COSTLY_ORDER
> >>          * means __GFP_NOFAIL, but that may not be true in other
> >>          * implementations.
> >
> > Eek, this is precisely what we don't want and is functionally the same as
> > what you initially proposed except it doesn't care about __GFP_NOFAIL.
> 
> This is checking against gfp_allowed_mask, not gfp_mask.
> 

gfp_allowed_mask is initialized to GFP_BOOT_MASK to start so that __GFP_FS 
is never allowed before the slab allocator is completely initialized, so 
you've now implicitly made all early boot allocations to be __GFP_NORETRY 
even though they may not pass it.