linux-kernel - Re: [PATCH 2/2] aio: fix the confliction of read events and migrating ring page

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Message-ID: <20140321173519.GB23173@kvack.org>
Date:	Fri, 21 Mar 2014 13:35:19 -0400
From:	Benjamin LaHaise <bcrl@...ck.org>
To:	Gu Zheng <guz.fnst@...fujitsu.com>
Cc:	Dave Jones <davej@...hat.com>, Al Viro <viro@...iv.linux.org.uk>,
	jmoyer@...hat.com, kosaki.motohiro@...fujitsu.com,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>,
	tangchen <tangchen@...fujitsu.com>, miaox@...fujitsu.com,
	linux-aio@...ck.org, fsdevel <linux-fsdevel@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 2/2] aio: fix the confliction of read events and migrating ring page

Hi Gu,

On Fri, Mar 21, 2014 at 09:56:36AM +0800, Gu Zheng wrote:
> This one is based on linux-next which has merged the following patch:
> commit 692c9b8c5ee8d263bb8348171f0bebd3d84eb2c1
> Author: Tang Chen <tangchen@...fujitsu.com>
> Date:   Mon Mar 10 16:15:33 2014 +0800
> aio, memory-hotplug: Fix confliction when migrating and accessing ring pages.
> 
> With this patch, the update of the ring's head pointer is safe because it is protected
> by completion_lock, so we do not need to enlarge the ring_lock protection region.
> And on the other side, if we take the ring_lock over the entire page migration
> operation, reading events will be affected if the page migration is going.

I have dropped this particular change of Tang's from my aio-next tree.  
The spinlock addition in the read events code path is not needed if we 
take the ring_lock mutex in the page migration code path.  This will 
ensure that we aren't needlessly regressing performance.  I'll send out 
my replacement patch in a couple of minutes.

		-ben
-- 
"Thought is the essence of where you are now."
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