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From: Johannes Weiner <hannes@saeurebad.de>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Ingo Molnar <mingo@elte.hu>, linux-kernel@vger.kernel.org,
       Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [v2.6.26] what's brewing in x86.git for v2.6.26
References: <20080416202338.GA6007@elte.hu>
	<20080417002552.5742ad65.akpm@linux-foundation.org>
	<20080417011401.ea3e70f0.akpm@linux-foundation.org>
Date: Thu, 17 Apr 2008 12:32:03 +0200
In-Reply-To: <20080417011401.ea3e70f0.akpm@linux-foundation.org> (Andrew
	Morton's message of "Thu, 17 Apr 2008 01:14:01 -0700")
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Hi,

Andrew Morton <akpm@linux-foundation.org> writes:

> - extensive damage to the page-flags patches
>
>   Did you check that all architectures and configurations still have
>   sufficient page flags for us to be able to consume another one for
>   kmemcheck?  The MM developers have put much, much effort into avoiding
>   running out of flags over numerous years and afaik none of them even know
>   that this debug feature is using one of the few remaining ones.
>
>   What do we do when we run out?

Would it be feasible to add another unsigned long to struct page?  I
mean, extending such a common structure always sucks, but for
emergency...

#define PageFoobar(page)	test_bit(PG_foobar, &(page)->flags2)

Of course the essential core flags should always be in ->flags but
perhaps we could have a symbol CONFIG_NEED_EXTRA_PAGE_FLAGS that gets
selected by kmemcheck (and other candidates that are unlikely to be
enabled most of the time) and then #ifndef ->flags2 out.

	Hannes