linux-kernel - Re: [PATCH] Only print kernel debug information for OOMs caused by kernel allocations

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Date:	Mon, 28 Jan 2008 10:11:57 +0100
From:	Andi Kleen <ak@...e.de>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] Only print kernel debug information for OOMs caused by kernel allocations

On Monday 28 January 2008 09:56, Andrew Morton wrote:
> On Mon, 28 Jan 2008 07:10:07 +0100 Andi Kleen <ak@...e.de> wrote:
> > On Monday 28 January 2008 06:52, Andrew Morton wrote:
> > > On Wed, 16 Jan 2008 23:24:21 +0100 Andi Kleen <ak@...e.de> wrote:
> > > > I recently suffered an 20+ minutes oom thrash disk to death and
> > > > computer completely unresponsive situation on my desktop when some
> > > > user program decided to grab all memory. It eventually recovered, but
> > > > left lots of ugly and imho misleading messages in the kernel log.
> > > > here's a minor improvement
> >
> > As a followup this was with swap over dm crypt. I've recently heard
> > about other people having trouble with this too so this setup seems to
> > trigger something bad in the VM.
>
> Where's the backtrace and show_mem() output? :)

I don't have it anymore. You want me to reproduce it? I don't think
I saw messages from the other people either; just heard complaints.

> > > That information is useful for working out why a userspace allocation
> > > attempt failed.  If we don't print it, and the application gets killed
> > > and thus frees a lot of memory, we will just never know why the
> > > allocation failed.
> >
> > But it's basically only either page fault (direct or indirect) or write
> > et.al. who do these page cache allocations. Do you really think it is
> > that important to distingush these cases individually? In 95+% of all
> > cases it should be a standard user page fault which always has the same
> > backtrace.
>
> Sure, the backtrace isn't very important.  The show_mem() output is vital.

I see. So would the patch be acceptable if it only disabled the backtrace? 

> Plus an additional function call.  On the already-deep page allocation
> path, I might add.

The function call is already there if the kernel has CPUSETs enabled.
And that is what distribution kernels usually do. And most users
use distribution kernels or distribution .config.

-Andi
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