linux-kernel - Re: CMA: test_pages_isolated failures in alloc_contig

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Message-ID: <xa1tfve8ku7q.fsf@mina86.com>
Date:	Tue, 28 Oct 2014 17:57:45 +0100
From:	Michal Nazarewicz <mina86@...a86.com>
To:	Peter Hurley <peter@...leysoftware.com>,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	linux-mm@...ck.org
Cc:	linux-kernel@...r.kernel.org, linux-sh@...r.kernel.org,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	Minchan Kim <minchan@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: CMA: test_pages_isolated failures in alloc_contig_range

> On 10/28/2014 08:38 AM, Michal Nazarewicz wrote:
>> Like Laura wrote, the message is not (should not be) a problem in
>> itself:
>
> [...]
>
>> So as you can see cma_alloc will try another part of the cma region if
>> test_pages_isolated fails.
>> 
>> Obviously, if CMA region is fragmented or there's enough space for only
>> one allocation of required size isolation failures will cause allocation
>> failures, so it's best to avoid them, but they are not always avoidable.
>> 
>> To debug you would probably want to add more debug information about the
>> page (i.e. data from struct page) that failed isolation after the
>> pr_warn in alloc_contig_range.

On Tue, Oct 28 2014, Peter Hurley <peter@...leysoftware.com> wrote:
> If the message does not indicate an actual problem, then its printk level is
> too high. These messages have been reported when using 3.16+ distro kernels.

I think it could be argued both ways.  The condition is not an error,
since in many cases cma_alloc will be able to continue, but it *is* an
undesired state.  As such it's not an error but feels to me a bit more
then just information, hence a warning.  I don't care either way, though.

-- 
Best regards,                                         _     _
.o. | Liege of Serenely Enlightened Majesty of      o' \,=./ `o
..o | Computer Science,  Michał “mina86” Nazarewicz    (o o)
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