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

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Message-ID: <20121106234949.GA24258@redhat.com>
Date:	Tue, 6 Nov 2012 18:49:49 -0500
From:	Dave Jones <davej@...hat.com>
To:	Nathan Zimmer <nzimmer@....com>
Cc:	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 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

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