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

[Stanislaw Gruszka <sgruszka@redhat.com>]

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@redhat.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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