Re: [PATCH 17/25] Do not call get_pageblock_migratetype() more than necessary

KOSAKI Motohiro
2009-04-21T11:03:13Z

> 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.