linux-kernel - Re: [rfc] increase struct page size?!

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Message-ID: <Pine.LNX.4.64.0705181633240.24071@blonde.wat.veritas.com>
Date:	Fri, 18 May 2007 16:42:10 +0100 (BST)
From:	Hugh Dickins <hugh@...itas.com>
To:	Nick Piggin <npiggin@...e.de>
cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux Memory Management List <linux-mm@...ck.org>,
	linux-arch@...r.kernel.org
Subject: Re: [rfc] increase struct page size?!

On Fri, 18 May 2007, Nick Piggin wrote:
> 
> If we add 8 bytes to struct page on 64-bit machines, it becomes 64 bytes,
> which is quite a nice number for cache purposes.
> 
> However we don't have to let those 8 bytes go to waste: we can use them
> to store the virtual address of the page, which kind of makes sense for
> 64-bit, because they can likely to use complicated memory models.

Sooner rather than later, don't we need those 8 bytes to expand from
atomic_t to atomic64_t _count and _mapcount?  Not that we really need
all 64 bits of both, but I don't know how to work atomically with less.

(Why do I have this sneaking feeling that you're actually wanting
to stick something into the lower bits of page->virtual?)

Hugh
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