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

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Date:	Wed, 26 Oct 2011 00:10:26 -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:

> > 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.
> 
> Only before interrupts are enabled, and then isn't it vulnerable to
> the same livelock?  Interrupts are off, single cpu, kswapd can't run.
> If an allocation ever failed, which seems unlikely, why would retrying
> help?
> 

If you want to claim gfp_allowed_mask as a pm-only entity, then I see no 
problem with this approach.  However, if gfp_allowed_mask would be allowed 
to temporarily change after init for another purpose then it would make 
sense to retry because another allocation with __GFP_FS on another cpu or 
kswapd could start making progress could allow for future memory freeing.

The suggestion to add a hook directly into a pm-interface was so that we 
could isolate it only to suspend and, to me, is the most maintainable 
solution.
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