linux-kernel - Re: [PATCH v5 7/8] mm: Only IPI CPUs to drain local pages if they exist

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Date:	Thu, 5 Jan 2012 16:35:29 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Mel Gorman <mel@....ul.ie>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	Gilad Ben-Yossef <gilad@...yossef.com>,
	linux-kernel@...r.kernel.org, Chris Metcalf <cmetcalf@...era.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Frederic Weisbecker <fweisbec@...il.com>, linux-mm@...ck.org,
	Pekka Enberg <penberg@...nel.org>,
	Matt Mackall <mpm@...enic.com>,
	Sasha Levin <levinsasha928@...il.com>,
	Rik van Riel <riel@...hat.com>,
	Andi Kleen <andi@...stfloor.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	linux-fsdevel@...r.kernel.org, Avi Kivity <avi@...hat.com>
Subject: Re: [PATCH v5 7/8] mm: Only IPI CPUs to drain local pages if they
	exist

On Thu, Jan 05, 2012 at 04:17:39PM +0000, Mel Gorman wrote:
> Link please?

Forwarded, as its still in my mailbox.

> I'm including a patch below under development that is
> intended to only cope with the page allocator case under heavy memory
> pressure. Currently it does not pass testing because eventually RCU
> gets stalled with the following trace
> 
> [ 1817.176001]  [<ffffffff810214d7>] arch_trigger_all_cpu_backtrace+0x87/0xa0
> [ 1817.176001]  [<ffffffff810c4779>] __rcu_pending+0x149/0x260
> [ 1817.176001]  [<ffffffff810c48ef>] rcu_check_callbacks+0x5f/0x110
> [ 1817.176001]  [<ffffffff81068d7f>] update_process_times+0x3f/0x80
> [ 1817.176001]  [<ffffffff8108c4eb>] tick_sched_timer+0x5b/0xc0
> [ 1817.176001]  [<ffffffff8107f28e>] __run_hrtimer+0xbe/0x1a0
> [ 1817.176001]  [<ffffffff8107f581>] hrtimer_interrupt+0xc1/0x1e0
> [ 1817.176001]  [<ffffffff81020ef3>] smp_apic_timer_interrupt+0x63/0xa0
> [ 1817.176001]  [<ffffffff81449073>] apic_timer_interrupt+0x13/0x20
> [ 1817.176001]  [<ffffffff8116c135>] vfsmount_lock_local_lock+0x25/0x30
> [ 1817.176001]  [<ffffffff8115c855>] path_init+0x2d5/0x370
> [ 1817.176001]  [<ffffffff8115eecd>] path_lookupat+0x2d/0x620
> [ 1817.176001]  [<ffffffff8115f4ef>] do_path_lookup+0x2f/0xd0
> [ 1817.176001]  [<ffffffff811602af>] user_path_at_empty+0x9f/0xd0
> [ 1817.176001]  [<ffffffff81154e7b>] vfs_fstatat+0x4b/0x90
> [ 1817.176001]  [<ffffffff81154f4f>] sys_newlstat+0x1f/0x50
> [ 1817.176001]  [<ffffffff81448692>] system_call_fastpath+0x16/0x1b
> 
> It might be a separate bug, don't know for sure.

I'm not going to even pretend to understand what the above backtrace
means: it doesn't look like what I'd expect from the problem which
PeterZ's patch is supposed to address.  It certainly doesn't do anything
to address the cpu-going-offline problem you seem to have found.
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