linux-kernel - Re: [PATCH 1/9] readahead: introduce PG

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Message-Id: <20070519081944.3caf4776.akpm@linux-foundation.org>
Date:	Sat, 19 May 2007 08:19:44 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Fengguang Wu <wfg@...l.ustc.edu.cn>, linux-kernel@...r.kernel.org,
	Jens Axboe <jens.axboe@...cle.com>,
	Oleg Nesterov <oleg@...sign.ru>,
	Steven Pratt <slpratt@...tin.ibm.com>,
	Ram Pai <linuxram@...ibm.com>
Subject: Re: [PATCH 1/9] readahead: introduce PG_readahead

On Sat, 19 May 2007 13:35:01 +0200 Andi Kleen <andi@...stfloor.org> wrote:

> > 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.
>  
> On 64bit there is no particular shortage of page flags.

I think pretty much all of the upper 32 bits got used for ia64 fields,
but it's never been very clear how many were actually used or needed.

> If you ever do racy things please do them 32bit only.

hrm.  It *really* won't matter if we make one suboptimal readahead decision
every second day.  And there's value in having the same behaviour on all
architectures.

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