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Date: Fri, 29 May 2009 23:53:02 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Andi Kleen <andi@firstfloor.org>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>, linux-kernel@vger.kernel.org,
       linux-mm@kvack.org, fengguang.wu@intel.com
Subject: Re: More thoughts about hwpoison and pageflags compression
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On Sat, 30 May 2009 08:37:10 +0200 Andi Kleen <andi@firstfloor.org> wrote:

> So using a separate bit is a sensible choice imho.

Could you make the feature 64-bit-only and use one of bits 32-63?

Did you consider making the poison tag external to the pageframe?  Some
hash(page*) into a bitmap or something?  If suitably designed, such
infrastructure could perhaps be reused to reclaim some existing page
flags.  Dave Hansen had such a patch a few years back.  Or maybe it
was Andy Whitcroft.