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    SubjectRe: [PATCH 17/25] Do not call get_pageblock_migratetype() more than necessary
    On Tue, Apr 21, 2009 at 08:03:10PM +0900, KOSAKI Motohiro wrote:
    > > get_pageblock_migratetype() is potentially called twice for every page
    > > free. Once, when being freed to the pcp lists and once when being freed
    > > back to buddy. When freeing from the pcp lists, it is known what the
    > > pageblock type was at the time of free so use it rather than rechecking.
    > > In low memory situations under memory pressure, this might skew
    > > anti-fragmentation slightly but the interference is minimal and
    > > decisions that are fragmenting memory are being made anyway.
    > >
    > > Signed-off-by: Mel Gorman <mel@csn.ul.ie>
    > > Reviewed-by: Christoph Lameter <cl@linux-foundation.org>
    > > ---
    > > mm/page_alloc.c | 16 ++++++++++------
    > > 1 files changed, 10 insertions(+), 6 deletions(-)
    > >
    > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
    > > index c57c602..a1ca038 100644
    > > --- a/mm/page_alloc.c
    > > +++ b/mm/page_alloc.c
    > > @@ -456,16 +456,18 @@ static inline int page_is_buddy(struct page *page, struct page *buddy,
    > > */
    > >
    > > static inline void __free_one_page(struct page *page,
    > > - struct zone *zone, unsigned int order)
    > > + struct zone *zone, unsigned int order,
    > > + int migratetype)
    > > {
    > > unsigned long page_idx;
    > > int order_size = 1 << order;
    > > - int migratetype = get_pageblock_migratetype(page);
    > >
    > > if (unlikely(PageCompound(page)))
    > > if (unlikely(destroy_compound_page(page, order)))
    > > return;
    > >
    > > + VM_BUG_ON(migratetype == -1);
    > > +
    > > page_idx = page_to_pfn(page) & ((1 << MAX_ORDER) - 1);
    > >
    > > VM_BUG_ON(page_idx & (order_size - 1));
    > > @@ -534,17 +536,18 @@ static void free_pages_bulk(struct zone *zone, int count,
    > > page = list_entry(list->prev, struct page, lru);
    > > /* have to delete it as __free_one_page list manipulates */
    > > list_del(&page->lru);
    > > - __free_one_page(page, zone, order);
    > > + __free_one_page(page, zone, order, page_private(page));
    > > }
    > > spin_unlock(&zone->lock);
    >
    > looks good.
    > Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
    >
    >
    > btw, I can't review rest patch today. I plan to do that tommorow, sorry.
    >

    No problem. Thanks a million for the work you've done so far. It was a
    big help and you caught a fair few problems in there.

    --
    Mel Gorman
    Part-time Phd Student Linux Technology Center
    University of Limerick IBM Dublin Software Lab


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