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Re: [PATCH 1/9] readahead: introduce PG_readahead

From:  Andrew Morton <akpm-AT-linux-foundation.org>
To:  Fengguang Wu <wfg-AT-mail.ustc.edu.cn>
Subject:  Re: [PATCH 1/9] readahead: introduce PG_readahead
Date:  Fri, 18 May 2007 23:28:24 -0700
Cc:  linux-kernel-AT-vger.kernel.org, Andi Kleen <andi-AT-firstfloor.org>, Jens Axboe <jens.axboe-AT-oracle.com>, Oleg Nesterov <oleg-AT-tv-sign.ru>, Steven Pratt <slpratt-AT-austin.ibm.com>, Ram Pai <linuxram-AT-us.ibm.com>
Archive-link:  Article, Thread

On Thu, 17 May 2007 06:47:53 +0800 Fengguang Wu <wfg@mail.ustc.edu.cn> wrote:

> Introduce a new page flag: PG_readahead.

Is there any way in which we can avoid adding a new page flag?

We have the advantage that if the kernel very occasionally gets the wrong
result for PageReadahead(page), nothing particularly bad will happen, so we
can do racy things.

From a quick peek, it appears that PG_readahead is only ever set against
non-uptodate pages.  If true we could perhaps exploit that: say,
PageReadahead(page) == PG_referenced && !PG_uptodate?


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