linux-kernel - Re: [v2.6.26] what's brewing in x86.git for v2.6.26

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Message-ID: <87skxkepr0.fsf@saeurebad.de>
Date:	Thu, 17 Apr 2008 12:32:03 +0200
From:	Johannes Weiner <hannes@...urebad.de>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [v2.6.26] what's brewing in x86.git for v2.6.26

Hi,

Andrew Morton <akpm@...ux-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
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