linux-kernel - Re: [PATCH v2 1/3] mm: more intensive memory corruption debug

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Date:	Wed, 23 Nov 2011 14:25:56 +0100
From:	Stanislaw Gruszka <sgruszka@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Mel Gorman <mgorman@...e.de>,
	Andrea Arcangeli <aarcange@...hat.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Christoph Lameter <cl@...ux-foundation.org>
Subject: Re: [PATCH v2 1/3] mm: more intensive memory corruption debug

On Tue, Nov 22, 2011 at 01:56:08PM -0800, Andrew Morton wrote:
> On Fri, 18 Nov 2011 17:25:05 +0100
> Stanislaw Gruszka <sgruszka@...hat.com> wrote:
> I added this:
> 
>   The default value of debug_guardpage_minorder is zero: no change
>   from current behaviour.
> 
> correct?
Yes,

> > +static inline void clear_page_guard_flg(struct page *page)
> > +{
> > +	__clear_bit(PAGE_DEBUG_FLAG_GUARD, &page->debug_flags);
> > +}
> 
> Why is it safe to use the non-atomic bitops here.
Clearing/setting flag is done only in __free_one_page()/expand(),
so operations are protected by zone->lock.

> Please verify that CONFIG_WANT_PAGE_DEBUG_FLAGS is always reliably
> enabled when this feature is turned on.
Change in mm/Kconfig.debug assures that CONFIG_WANT_PAGE_DEBUG_FLAGS is
set whenever CONFIG_DEBUG_PAGEALLOC is. 

> Some changes I made - please review.
Look good, thanks Andrew!

Stanislaw
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