Re: [PATCH 1/4] pull out the page pre-release and sanity check logic for reuse

Andy Whitcroft
2008-09-08T15:14:13Z

On Mon, Sep 08, 2008 at 11:11:22PM +0900, MinChan Kim wrote:
> 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.

> > + 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