linux-kernel - Re: [PATCH 2/2] Optimize compound_head() by avoiding a shared page flag

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Message-ID: <Pine.LNX.4.64.0704071718530.31790@schroedinger.engr.sgi.com>
Date:	Sat, 7 Apr 2007 17:21:38 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	Hugh Dickins <hugh@...itas.com>, Nick Piggin <npiggin@...e.de>,
	dgc@....com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] Optimize compound_head() by avoiding a shared page
 flag

On Sat, 7 Apr 2007, Andrew Morton wrote:

> Which is all a ton of fun, but this subversion of the architecture's
> freedom to use volatile, memory barriers etc is a worry.  We do the same in
> page_alloc.c, of course...  

I just tried the approach that we discussed earlier and it was not 
nice either. Lets just use a page flag please. This check will be in 
several hot code paths. And it may become more important because the file 
system folks want to support buffers > page size. Then we may want more 
transparent support for huge pages... For all of this page->private gets 
in the way.

And I think we curently have 5 or so page flags available?

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