linux-kernel - Re: [PATCH] mm: SLAB Out-of-memory diagnostics

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Date:	Wed, 29 Feb 2012 09:37:23 +0200 (EET)
From:	Pekka Enberg <penberg@...nel.org>
To:	Rafael Aquini <aquini@...hat.com>
cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Randy Dunlap <rdunlap@...otime.net>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Matt Mackall <mpm@...enic.com>, Rik van Riel <riel@...hat.com>,
	Josef Bacik <josef@...hat.com>,
	David Rientjes <rientjes@...gle.com>
Subject: Re: [PATCH] mm: SLAB Out-of-memory diagnostics

On Wed, 29 Feb 2012, Rafael Aquini wrote:
> Following the example at mm/slub.c, add out-of-memory diagnostics to the SLAB
> allocator to help on debugging OOM conditions. This patch also adds a new
> sysctl, 'oom_dump_slabs_forced', that overrides the effect of __GFP_NOWARN page
> allocation flag and forces the kernel to report every slab allocation failure.
> 
> An example print out looks like this:
> 
>   <snip page allocator out-of-memory message>
>   SLAB: Unable to allocate memory on node 0 (gfp=0x11200)
>      cache: bio-0, object size: 192, order: 0
>      node0: slabs: 3/3, objs: 60/60, free: 0
> 
> Signed-off-by: Rafael Aquini <aquini@...hat.com>
> ---
>  Documentation/sysctl/vm.txt |   23 ++++++++++++++++++
>  include/linux/slab.h        |    2 +
>  kernel/sysctl.c             |    9 +++++++
>  mm/slab.c                   |   55 ++++++++++++++++++++++++++++++++++++++++++-
>  4 files changed, 88 insertions(+), 1 deletions(-)

No SLUB support for this?

> diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt
> index 96f0ee8..75bdf91 100644
> --- a/Documentation/sysctl/vm.txt
> +++ b/Documentation/sysctl/vm.txt
> @@ -498,6 +498,29 @@ this is causing problems for your system/application.
>  
>  ==============================================================
>  
> +oom_dump_slabs_forced
> +
> +Overrides the effects of __GFP_NOWARN page allocation flag, thus forcing
> +the system to print warnings about every allocation failure for the
> +slab allocator, and helping on debugging certain OOM conditions.
> +The print out is pretty similar, and complements data that is reported by
> +the page allocator out-of-memory warning:
> +
> +<snip page allocator out-of-memory message>
> +  SLAB: Unable to allocate memory on node 0 (gfp=0x11200)
> +     cache: bio-0, object size: 192, order: 0
> +     node0: slabs: 3/3, objs: 60/60, free: 0
> +
> +If this is set to zero, the default behavior is observed and warnings will only
> +be printed out for allocation requests that didn't set the __GFP_NOWARN flag.
> +
> +When set to non-zero, this information is shown whenever the allocator finds
> +itself failing to grant a request, regardless the __GFP_NOWARN flag status.
> +
> +The default value is 0 (disabled).
> +
> +==============================================================
> +

Why do you want to add a sysctl for this? That'd be an ABI that we need to 
keep around forever.

Is there any reason we shouldn't just enable this unconditionally?

			Pekka
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