From mboxrd@z Thu Jan  1 00:00:00 1970
From: Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH 09/27] nfs: writeback pages wait queue
Date: Fri, 04 Mar 2011 10:26:35 +0100
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References: <20110303064505.718671603@intel.com>
	 <20110303074949.809203319@intel.com> <1299168481.1310.56.camel@laptop>
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Cc: Andrew Morton <akpm@linux-foundation.org>, Jan Kara <jack@suse.cz>,
 Jens Axboe <axboe@kernel.dk>, Chris Mason <chris.mason@oracle.com>, Trond
 Myklebust <Trond.Myklebust@netapp.com>, Christoph Hellwig <hch@lst.de>,
 Dave Chinner <david@fromorbit.com>, Theodore Ts'o <tytso@mit.edu>, Mel
 Gorman <mel@csn.ul.ie>,  Rik van Riel <riel@redhat.com>, KOSAKI Motohiro
 <kosaki.motohiro@jp.fujitsu.com>, Greg Thelen <gthelen@google.com>, Minchan
 Kim <minchan.kim@gmail.com>, Vivek Goyal <vgoyal@redhat.com>, Andrea Righi
 <arighi@develer.com>, Balbir Singh <balbir@linux.vnet.ibm.com>, linux-mm
 <linux-mm@kvack.org>,  "linux-fsdevel@vger.kernel.org"
 <linux-fsdevel@vger.kernel.org>, LKML <linux-kernel@vger.kernel.org>
To: Wu Fengguang <fengguang.wu@intel.com>
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On Fri, 2011-03-04 at 10:10 +0100, Peter Zijlstra wrote:
> On Fri, 2011-03-04 at 10:01 +0800, Wu Fengguang wrote:
> >                         clear_bdi_congested(bdi, BLK_RW_SYNC);
> >                         /*
> >                          * On the following wake_up(), nfs_wait_congest=
ed()
> >                          * will see the cleared bit and quit.
> >                          */
> >                         smp_mb__after_clear_bit();
> >                 }
> >                 if (waitqueue_active(&wqh[BLK_RW_SYNC]))
> >                         wake_up(&wqh[BLK_RW_SYNC]);=20
>=20
> If I tell you that: try_to_wake_up() implies an smp_wmb(), do you then
> still need this?

Also, there is no matching rmb,mb in nfs_wait_congested().. barrier
always come in pairs.

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