Date: Sat, 19 May 2007 08:19:44 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Andi Kleen <andi@firstfloor.org>
Cc: Fengguang Wu <wfg@mail.ustc.edu.cn>, linux-kernel@vger.kernel.org,
       Jens Axboe <jens.axboe@oracle.com>, Oleg Nesterov <oleg@tv-sign.ru>,
       Steven Pratt <slpratt@austin.ibm.com>, Ram Pai <linuxram@us.ibm.com>
Subject: Re: [PATCH 1/9] readahead: introduce PG_readahead
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On Sat, 19 May 2007 13:35:01 +0200 Andi Kleen <andi@firstfloor.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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