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

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Date:	Tue, 25 Oct 2011 23:26:40 -0700
From:	Colin Cross <ccross@...roid.com>
To:	David Rientjes <rientjes@...gle.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, Oct 25, 2011 at 11:24 PM, David Rientjes <rientjes@...gle.com> wrote:
> On Tue, 25 Oct 2011, Colin Cross wrote:
>
>> > Or, rather, when pm_restrict_gfp_mask() clears __GFP_IO and __GFP_FS that
>> > it also has the same behavior as __GFP_NORETRY in should_alloc_retry() by
>> > setting a variable in file scope.
>> >
>>
>> Why do you prefer that over adding a gfp_required_mask?
>>
>
> Because it avoids an unnecessary OR in the page and slab allocator
> fastpaths which are red hot :)
>

Makes sense.  What about this?  Official patch to follow.

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.
--
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