linux-kernel - Re: [PATCH 1/4] compcache: xvmalloc memory allocator

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Message-ID: <alpine.DEB.1.10.0908261204400.9933@gentwo.org>
Date:	Wed, 26 Aug 2009 12:07:47 -0400 (EDT)
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	Nitin Gupta <ngupta@...are.org>
cc:	Pekka Enberg <penberg@...helsinki.fi>, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linux-mm-cc@...top.org
Subject: Re: [PATCH 1/4] compcache: xvmalloc memory allocator

On Tue, 25 Aug 2009, Nitin Gupta wrote:

> PFNs are 32-bit on all archs while for 'struct page *', we require 32-bit or
> 64-bit depending on arch. ramzswap allocates a table entry <pagenum, offset>
> corresponding to every swap slot. So, the size of table will unnecessarily
> increase on 64-bit archs. Same is the argument for xvmalloc free list sizes.

Wrong. PFNs must be longer than 32 bit otherwise a system cannot
address more than 2^12 + 2^32 = 2^44 =>  16TB.

The type used for PFNs is unsigned long which are 64 bit on 64 bit platforms.

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