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

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Message-ID: <5388B8D7.1020907@wwwdotorg.org>
Date:	Fri, 30 May 2014 10:59:03 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Vlastimil Babka <vbabka@...e.cz>, Shawn Guo <shawn.guo@...aro.org>,
	Kevin Hilman <khilman@...aro.org>,
	Andrew Morton <akpm@...ux-foundation.org>
CC:	Joonsoo Kim <iamjoonsoo.kim@....com>,
	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>,
	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 05/23/2014 02:34 AM, Vlastimil Babka wrote:
> On 05/23/2014 04:48 AM, Shawn Guo wrote:
>> 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
>>
> 
> Really sorry, guys :/
> 
> -----8<-----
> From: Vlastimil Babka <vbabka@...e.cz>
> Date: Fri, 23 May 2014 10:18:56 +0200
> Subject: mm-compaction-properly-signal-and-act-upon-lock-and-need_sched-contention-fix2
> 
> Step 1: Change function name and comment between v1 and v2 so that the return
>         value signals the opposite thing.
> Step 2: Change the call sites to reflect the opposite return value.
> Step 3: ???
> Step 4: Make a complete fool of yourself.

Tested-by: Stephen Warren <swarren@...dia.com>

This fix doesn't seem to be in linux-next yet:-(
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