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

    > + 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);
    > --
    > 1.6.0.rc1.258.g80295
    >
    > --
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    >



    --
    Thanks,
    MinChan Kim


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