Subject: [PATCH v2] mm, compaction: properly signal and act upon lock and need_sched() contention

From: [email-masked] (Kevin Hilman)
Date: Fri, 23 May 2014 08:07:06 -0700

Vlastimil Babka <[email-masked]> writes:

> On 05/23/2014 04:48 AM, Shawn Guo wrote:
>> On 23 May 2014 07:49, Kevin Hilman <[email-masked]> wrote:
>>> On Fri, May 16, 2014 at 2:47 AM, Vlastimil Babka <[email-masked]> 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 <[email-masked]>
> 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.
> Signed-off-by: Vlastimil Babka <[email-masked]>

Tested-by: Kevin Hilman <[email-masked]>

I verified that this fixes the boot failures I've seen on ARM (i.MX6 and
Marvell Armada 370).

Thanks for the quick fix.

Kevin