linux-kernel - Re: [PATCH v2] mm, compaction: properly signal and act upon lock and need

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Date:	Fri, 23 May 2014 10:48:29 +0800
From:	Shawn Guo <shawn.guo@...aro.org>
To:	Kevin Hilman <khilman@...aro.org>
Cc:	Vlastimil Babka <vbabka@...e.cz>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Rientjes <rientjes@...gle.com>,
	Hugh Dickins <hughd@...gle.com>,
	Greg Thelen <gthelen@...gle.com>,
	LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org,
	Minchan Kim <minchan@...nel.org>, Mel Gorman <mgorman@...e.de>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	Michal Nazarewicz <mina86@...a86.com>,
	Christoph Lameter <cl@...ux.com>,
	Rik van Riel <riel@...hat.com>,
	Olof Johansson <olof@...om.net>,
	Stephen Warren <swarren@...dotorg.org>,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2] mm, compaction: properly signal and act upon lock and
 need_sched() contention

On 23 May 2014 07:49, Kevin Hilman <khilman@...aro.org> wrote:
> On Fri, May 16, 2014 at 2:47 AM, Vlastimil Babka <vbabka@...e.cz> wrote:
>> Compaction uses compact_checklock_irqsave() function to periodically check for
>> lock contention and need_resched() to either abort async compaction, or to
>> free the lock, schedule and retake the lock. When aborting, cc->contended is
>> set to signal the contended state to the caller. Two problems have been
>> identified in this mechanism.
>
> This patch (or later version) has hit next-20140522 (in the form
> commit 645ceea9331bfd851bc21eea456dda27862a10f4) and according to my
> bisect, appears to be the culprit of several boot failures on ARM
> platforms.

On i.MX6 where CMA is enabled, the commit causes the drivers calling
dma_alloc_coherent() fail to probe.  Tracing it a little bit, it seems
dma_alloc_from_contiguous() always return page as NULL after this
commit.

Shawn
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