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

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Message-ID: <alpine.DEB.2.00.1110251510240.26017@chino.kir.corp.google.com>
Date:	Tue, 25 Oct 2011 15:12:26 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Colin Cross <ccross@...roid.com>
cc:	Pekka Enberg <penberg@...helsinki.fi>,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>,
	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_KERNEL is __GFP_WAIT | __GFP_IO | __GFP_FS.  Once driver suspend
> has started, gfp_allowed_mask is ~(__GFP_IO | GFP_FS), so any call to
> __alloc_pages_nodemask(GFP_KERNEL, ...) gets masked to effectively
> __alloc_pages_nodemask(__GFP_WAIT, ...).
> 

Just passing __GFP_WAIT is the problem that you're trying to address, 
though.  Why not include __GFP_NORETRY since you know the liklihood of 
allocation being successful on the second iteration is very slim since 
you're not in a context where you can force reclaim or oom killing?

> The loop is in __alloc_pages_slowpath, from the rebalance label to
> should_alloc_retry.

The loop is by design and is activated because you're just passing 
__GFP_WAIT in this context for no sensible reason.
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