Date: Fri, 12 Mar 2004 21:51:04 +0100
From: Jens Axboe <axboe@suse.de>
To: Chris Mason <mason@suse.com>
Cc: Andrew Morton <akpm@osdl.org>, linux-kernel@vger.kernel.org,
       kenneth.w.chen@intel.com
Subject: Re: [PATCH] per-backing dev unplugging #2
Message-ID: <20040312205104.GE16880@suse.de>
References: <20040311083619.GH6955@suse.de> <1079121113.4181.189.camel@watt.suse.com> <20040312120322.0108a437.akpm@osdl.org> <20040312200253.GA16880@suse.de> <1079123647.4186.211.camel@watt.suse.com> <20040312203452.GD16880@suse.de> <1079124097.4187.216.camel@watt.suse.com>
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On Fri, Mar 12 2004, Chris Mason wrote:
> On Fri, 2004-03-12 at 15:34, Jens Axboe wrote:
> 
> > 
> > I don't see how this can make too much of a difference, aside of perhaps
> > just moving the window a little. If page->mapping can disappear here,
> > that's still a possibility.
> 
> As Andrew pointed out, the mapping struct won't disappear, but
> page->mapping may go null.  So the idea is to use barriers to get a
> trusted copy of page->mapping, and use the copy everywhere.

So trusting an atomic assignment of mapping = page->mapping, it should
work. It feels a bit icky, though.

-- 
Jens Axboe

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