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Date: Fri, 23 May 2014 10:48:29 +0800
Message-ID: <CAAQ0ZWQDVxAzZVm86ATXd1JGUVoLXj_Y5Ske7htxH_6a4GPKRg@mail.gmail.com>
Subject: Re: [PATCH v2] mm, compaction: properly signal and act upon lock and
 need_sched() contention
From: Shawn Guo <shawn.guo@linaro.org>
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To: Kevin Hilman <khilman@linaro.org>
Cc: Vlastimil Babka <vbabka@suse.cz>, Joonsoo Kim <iamjoonsoo.kim@lge.com>, Andrew Morton <akpm@linux-foundation.org>, David Rientjes <rientjes@google.com>, Hugh Dickins <hughd@google.com>, Greg Thelen <gthelen@google.com>, LKML <linux-kernel@vger.kernel.org>, linux-mm@kvack.org, Minchan Kim <minchan@kernel.org>, Mel Gorman <mgorman@suse.de>, Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>, Michal Nazarewicz <mina86@mina86.com>, Christoph Lameter <cl@linux.com>, Rik van Riel <riel@redhat.com>, Olof Johansson <olof@lixom.net>, Stephen Warren <swarren@wwwdotorg.org>, linux-arm-kernel <linux-arm-kernel@lists.infradead.org>

On 23 May 2014 07:49, Kevin Hilman <khilman@linaro.org> wrote:
> On Fri, May 16, 2014 at 2:47 AM, Vlastimil Babka <vbabka@suse.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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