On Mon, Sep 08, 2008 at 11:11:22PM +0900, MinChan Kim wrote:
quoted text
> On Fri, Sep 5, 2008 at 7:19 PM, Andy Whitcroft <apw@shadowen.org> wrote:
> > When we are about to release a page we perform a number of actions
> > on that page.  We clear down any anonymous mappings, confirm that
> > the page is safe to release, check for freeing locks, before mapping
> > the page should that be required.  Pull this processing out into a
> > helper function for reuse in a later patch.
> >
> > Note that we do not convert the similar cleardown in free_hot_cold_page()
> > as the optimiser is unable to squash the loops during the inline.
> >
> > Signed-off-by: Andy Whitcroft <apw@shadowen.org>
> > Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
> > Acked-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
> > Reviewed-by: Rik van Riel <riel@redhat.com>
> > ---
> >  mm/page_alloc.c |   43 ++++++++++++++++++++++++++++++-------------
> >  1 files changed, 30 insertions(+), 13 deletions(-)
> >
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index f52fcf1..b2a2c2b 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -489,6 +489,35 @@ static inline int free_pages_check(struct page *page)
> >  }
> >
> >  /*
> > + * Prepare this page for release to the buddy.  Sanity check the page.
> > + * Returns 1 if the page is safe to free.
> > + */
> > +static inline int free_page_prepare(struct page *page, int order)
> > +{
> > +       int i;
> > +       int reserved = 0;
> > +
> > +       if (PageAnon(page))
> > +               page->mapping = NULL;
> 
> Why do you need to clear down anonymous mapping ?
> I think if you don't convert this cleardown in free_hot_cold_page(),
> you don't need it.
> 
> If you do it, bad_page can't do his role.

Yeah that has slipped through from where originally this patch used to
merge two different instances of this code.  Good spot.  Will sort that
out.

quoted text
> > +       for (i = 0 ; i < (1 << order) ; ++i)
> > +               reserved += free_pages_check(page + i);
> > +       if (reserved)
> > +               return 0;
> > +
> > +       if (!PageHighMem(page)) { > > +               debug_check_no_locks_freed(page_address(page),
> > +                                                       PAGE_SIZE << order);
> > +               debug_check_no_obj_freed(page_address(page),
> > +                                          PAGE_SIZE << order);
> > +       }
> > +       arch_free_page(page, order);
> > +       kernel_map_pages(page, 1 << order, 0);
> > +
> > +       return 1;
> > +}
> > +
> > +/*
> >  * Frees a list of pages.
> >  * Assumes all pages on list are in same zone, and of same order.
> >  * count is the number of pages to free.
> > @@ -529,22 +558,10 @@ static void free_one_page(struct zone *zone, struct page *page, int order)
> >  static void __free_pages_ok(struct page *page, unsigned int order)
> >  {
> >        unsigned long flags;
> > -       int i;
> > -       int reserved = 0;
> >
> > -       for (i = 0 ; i < (1 << order) ; ++i)
> > -               reserved += free_pages_check(page + i);
> > -       if (reserved)
> > +       if (!free_page_prepare(page, order))
> >                return;
> >
> > -       if (!PageHighMem(page)) {
> > -               debug_check_no_locks_freed(page_address(page),PAGE_SIZE<<order);
> > -               debug_check_no_obj_freed(page_address(page),
> > -                                          PAGE_SIZE << order);
> > -       }
> > -       arch_free_page(page, order);
> > -       kernel_map_pages(page, 1 << order, 0);
> > -
> >        local_irq_save(flags);
> >        __count_vm_events(PGFREE, 1 << order);
> >        free_one_page(page_zone(page), page, order);

-apw
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