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

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Message-ID: <20111122123001.GA16054@localhost>
Date:	Tue, 22 Nov 2011 20:30:01 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Jan Kara <jack@...e.cz>
Cc:	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	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

> > @@ -1743,6 +1738,8 @@ void account_page_dirtied(struct page *p
> >  		__inc_bdi_stat(mapping->backing_dev_info, BDI_DIRTIED);
> >  		task_dirty_inc(current);
> >  		task_io_account_write(PAGE_CACHE_SIZE);
> > +		current->nr_dirtied++;
> > +		__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...

Hmm, I'm not worried about it at all, because bdp_ratelimits don't
need to be accurate. In normal cases it won't even trigger one single
call to balance_dirty_pages().

btw, account_page_dirtied() is called inside spinlock, will it be
sufficient?

Thanks,
Fengguang
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