linux-kernel - Re: [PATCH v2 04/11] memcg: disable softirq in lock_page

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Message-Id: <20101018094437.e12aae49.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Mon, 18 Oct 2010 09:44:37 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Greg Thelen <gthelen@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	containers@...ts.osdl.org, Andrea Righi <arighi@...eler.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	Minchan Kim <minchan.kim@...il.com>,
	Ciju Rajan K <ciju@...ux.vnet.ibm.com>,
	David Rientjes <rientjes@...gle.com>
Subject: Re: [PATCH v2 04/11] memcg: disable softirq in lock_page_cgroup()

On Fri, 15 Oct 2010 14:14:32 -0700
Greg Thelen <gthelen@...gle.com> wrote:

> If pages are being migrated from a memcg, then updates to that
> memcg's page statistics are protected by grabbing a bit spin lock
> using lock_page_cgroup().  In an upcoming commit memcg dirty page
> accounting will be updating memcg page accounting (specifically:
> num writeback pages) from softirq.  Avoid a deadlocking nested
> spin lock attempt by disabling softirq on the local processor
> when grabbing the page_cgroup bit_spin_lock in lock_page_cgroup().
> This avoids the following deadlock:
> statistic
>       CPU 0             CPU 1
>                     inc_file_mapped
>                     rcu_read_lock
>   start move
>   synchronize_rcu
>                     lock_page_cgroup
>                       softirq
>                       test_clear_page_writeback
>                       mem_cgroup_dec_page_stat(NR_WRITEBACK)
>                       rcu_read_lock
>                       lock_page_cgroup   /* deadlock */
>                       unlock_page_cgroup
>                       rcu_read_unlock
>                     unlock_page_cgroup
>                     rcu_read_unlock
> 
> By disabling softirq in lock_page_cgroup, nested calls are avoided.
> The softirq would be delayed until after inc_file_mapped enables
> softirq when calling unlock_page_cgroup().
> 
> The normal, fast path, of memcg page stat updates typically
> does not need to call lock_page_cgroup(), so this change does
> not affect the performance of the common case page accounting.
> 
> Signed-off-by: Andrea Righi <arighi@...eler.com>
> Signed-off-by: Greg Thelen <gthelen@...gle.com>

I have a patch for this problem.
So, could you reorder patch as

	1,2,3,5,6,7,8,9,10,11 

I'll post an add-on patch."12"

move_charge performance improbement patches will be posted later.

Thanks,
-Kame

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