linux-kernel - Re: [PATCH 00/10] foundations for reserve-based allocation

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Date:	Mon, 06 Aug 2007 21:36:58 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Daniel Phillips <phillips@...nq.net>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	David Miller <davem@...emloft.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Daniel Phillips <phillips@...gle.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Christoph Lameter <clameter@....com>,
	Matt Mackall <mpm@...enic.com>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Steve Dickson <SteveD@...hat.com>
Subject: Re: [PATCH 00/10] foundations for reserve-based allocation

On Mon, 2007-08-06 at 12:31 -0700, Daniel Phillips wrote:
> On Monday 06 August 2007 11:17, Peter Zijlstra wrote:
> > And how do we know a page was taken out of the reserves?
> 
> Why not return that in the low bit of the page address?  This is a 
> little more cache efficient, does not leave that odd footprint in the 
> page union and forces the caller to examine the 
> alloc_pages(...P_MEMALLOC) return, making it harder to overlook the 
> fact that it got a page out of reserve and forget to put one back 
> later.

This would require auditing all page allocation sites to ensure they
ever happen under PF_MEMALLOC or the like. Because if an allocator ever
fails to check the low bit and assumes its a valid struct page *, stuff
will go *bang*.



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