linux-kernel - Re: [PATCH 3/5] writeback: fix dirtied pages accounting on sub-page writes

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Date:	Tue, 22 Nov 2011 13:57:42 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Jan Kara <jack@...e.cz>
Cc:	Wu Fengguang <fengguang.wu@...el.com>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	Christoph Hellwig <hch@....de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/5] writeback: fix dirtied pages accounting on sub-page
 writes

On Tue, 2011-11-22 at 13:21 +0100, Jan Kara wrote:
> > +             __get_cpu_var(bdp_ratelimits)++;
>   I think you need preempt_disable() and preempt_enable() pair around
> __get_cpu_var(). Otherwise a process could get rescheduled in the middle of
> read-modify-write cycle... 

there's of course the this_cpu_inc(bdp_ratelimits); thing.

On x86 that'll turn into a single insn, on others it will add the
required preempt_disable/enable bits.
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