linux-kernel - Re: [RFC 2/2] procfs: /proc/sched_debug fails on very very large machines.

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Date:	Wed, 7 Nov 2012 09:58:41 -0600
From:	Nathan Zimmer <nzimmer@....com>
To:	Dave Jones <davej@...hat.com>, Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [RFC 2/2] procfs: /proc/sched_debug fails on very very large
 machines.

On 11/06/2012 05:49 PM, Dave Jones wrote:
> On Tue, Nov 06, 2012 at 05:24:15PM -0600, Nathan Zimmer wrote:
>   > On Tue, Nov 06, 2012 at 04:31:28PM -0500, Dave Jones wrote:
>   > > On Tue, Nov 06, 2012 at 03:02:21PM -0600, Nathan Zimmer wrote:
>   > >  > On systems with 4096 cores attemping to read /proc/sched_debug fails.
>   > >  > We are trying to push all the data into a single kmalloc buffer.
>   > >  > The issue is on these very large machines all the data will not fit in 4mb.
>   > >  >
>   > >  > A better solution is to not us the single_open mechanism but to provide
>   > >  > our own seq_operations and treat each cpu as an individual record.
>   > >
>   > > Good timing.
>   > >
>   > > This looks like it would solve the problem I just reported here:
>   > > https://lkml.org/lkml/2012/11/6/390
>   > >
>   > > That happens even on an 8-way, so it's not just niche machines that have
>   > > this problems.
>   >
>   > Glad to help. I hadn't thought of memory tight situation but it does make sense
>   > that it helps as it can get by with 4k allocation vs grabbing successively
>   > large chucks.
>   >
>   > If you have seen similar issues with your fuzz testing let me know where and
>   > I'll take a look.
>
> I think /proc/timer_list could probably use the same treatment.
> I had traces showing that using 64k allocations too, but I think I may have
> just bricked my testbox.
>
> 	Dave
>

Yup it looks like /proc/timer_list is doing the thing with single open.

nzimmer@...p50-sys:~> cat /proc/timer_list
cat: /proc/timer_list: Cannot allocate memory
nzimmer@...p50-sys:~>

I'll see if I can squeeze that one in too.
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