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Date: Tue, 17 Feb 2015 10:42:35 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: Joonsoo Kim <iamjoonsoo.kim@....com>,
Andrew Morton <akpm@...ux-foundation.org>
CC: Mel Gorman <mgorman@...e.de>, David Rientjes <rientjes@...gle.com>,
Rik van Riel <riel@...hat.com>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org,
Zhang Yanfei <zhangyanfei@...fujitsu.com>
Subject: Re: [PATCH v4 2/3] mm/page_alloc: factor out fallback freepage checking
On 02/12/2015 08:15 AM, Joonsoo Kim wrote:
> This is preparation step to use page allocator's anti fragmentation logic
> in compaction. This patch just separates fallback freepage checking part
> from fallback freepage management part. Therefore, there is no functional
> change.
>
> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>
Acked-by: Vlastimil Babka <vbabka@...e.cz>
> ---
> mm/page_alloc.c | 143 +++++++++++++++++++++++++++++++++++--------------------
> 1 file changed, 91 insertions(+), 52 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index e64b260..64a4974 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1142,14 +1142,40 @@ static void change_pageblock_range(struct page *pageblock_page,
> * as fragmentation caused by those allocations polluting movable pageblocks
> * is worse than movable allocations stealing from unmovable and reclaimable
> * pageblocks.
> - *
> - * If we claim more than half of the pageblock, change pageblock's migratetype
> - * as well.
> */
> -static void try_to_steal_freepages(struct zone *zone, struct page *page,
> - int start_type, int fallback_type)
> +static bool can_steal_fallback(unsigned int order, int start_mt)
> +{
> + /*
> + * Leaving this order check is intended, although there is
> + * relaxed order check in next check. The reason is that
> + * we can actually steal whole pageblock if this condition met,
> + * but, below check doesn't guarantee it and that is just heuristic
> + * so could be changed anytime.
> + */
> + if (order >= pageblock_order)
> + return true;
> +
> + if (order >= pageblock_order / 2 ||
> + start_mt == MIGRATE_RECLAIMABLE ||
> + start_mt == MIGRATE_UNMOVABLE ||
> + page_group_by_mobility_disabled)
> + return true;
> +
> + return false;
> +}
> +
> +/*
> + * This function implements actual steal behaviour. If order is large enough,
> + * we can steal whole pageblock. If not, we first move freepages in this
> + * pageblock and check whether half of pages are moved or not. If half of
> + * pages are moved, we can change migratetype of pageblock and permanently
> + * use it's pages as requested migratetype in the future.
> + */
> +static void steal_suitable_fallback(struct zone *zone, struct page *page,
> + int start_type)
> {
> int current_order = page_order(page);
> + int pages;
>
> /* Take ownership for orders >= pageblock_order */
> if (current_order >= pageblock_order) {
> @@ -1157,19 +1183,40 @@ static void try_to_steal_freepages(struct zone *zone, struct page *page,
> return;
> }
>
> - if (current_order >= pageblock_order / 2 ||
> - start_type == MIGRATE_RECLAIMABLE ||
> - start_type == MIGRATE_UNMOVABLE ||
> - page_group_by_mobility_disabled) {
> - int pages;
> + pages = move_freepages_block(zone, page, start_type);
> +
> + /* Claim the whole block if over half of it is free */
> + if (pages >= (1 << (pageblock_order-1)) ||
> + page_group_by_mobility_disabled)
> + set_pageblock_migratetype(page, start_type);
> +}
> +
> +/* Check whether there is a suitable fallback freepage with requested order. */
> +static int find_suitable_fallback(struct free_area *area, unsigned int order,
> + int migratetype, bool *can_steal)
> +{
> + int i;
> + int fallback_mt;
> +
> + if (area->nr_free == 0)
> + return -1;
> +
> + *can_steal = false;
> + for (i = 0;; i++) {
> + fallback_mt = fallbacks[migratetype][i];
> + if (fallback_mt == MIGRATE_RESERVE)
> + break;
> +
> + if (list_empty(&area->free_list[fallback_mt]))
> + continue;
>
> - pages = move_freepages_block(zone, page, start_type);
> + if (can_steal_fallback(order, migratetype))
> + *can_steal = true;
>
> - /* Claim the whole block if over half of it is free */
> - if (pages >= (1 << (pageblock_order-1)) ||
> - page_group_by_mobility_disabled)
> - set_pageblock_migratetype(page, start_type);
> + return fallback_mt;
> }
> +
> + return -1;
> }
>
> /* Remove an element from the buddy allocator from the fallback list */
> @@ -1179,53 +1226,45 @@ __rmqueue_fallback(struct zone *zone, unsigned int order, int start_migratetype)
> struct free_area *area;
> unsigned int current_order;
> struct page *page;
> + int fallback_mt;
> + bool can_steal;
>
> /* Find the largest possible block of pages in the other list */
> for (current_order = MAX_ORDER-1;
> current_order >= order && current_order <= MAX_ORDER-1;
> --current_order) {
> - int i;
> - for (i = 0;; i++) {
> - int migratetype = fallbacks[start_migratetype][i];
> - int buddy_type = start_migratetype;
> -
> - /* MIGRATE_RESERVE handled later if necessary */
> - if (migratetype == MIGRATE_RESERVE)
> - break;
> -
> - area = &(zone->free_area[current_order]);
> - if (list_empty(&area->free_list[migratetype]))
> - continue;
> -
> - page = list_entry(area->free_list[migratetype].next,
> - struct page, lru);
> - area->nr_free--;
> -
> - try_to_steal_freepages(zone, page, start_migratetype,
> - migratetype);
> + area = &(zone->free_area[current_order]);
> + fallback_mt = find_suitable_fallback(area, current_order,
> + start_migratetype, &can_steal);
> + if (fallback_mt == -1)
> + continue;
>
> - /* Remove the page from the freelists */
> - list_del(&page->lru);
> - rmv_page_order(page);
> + page = list_entry(area->free_list[fallback_mt].next,
> + struct page, lru);
> + if (can_steal)
> + steal_suitable_fallback(zone, page, start_migratetype);
>
> - expand(zone, page, order, current_order, area,
> - buddy_type);
> + /* Remove the page from the freelists */
> + area->nr_free--;
> + list_del(&page->lru);
> + rmv_page_order(page);
>
> - /*
> - * The freepage_migratetype may differ from pageblock's
> - * migratetype depending on the decisions in
> - * try_to_steal_freepages(). This is OK as long as it
> - * does not differ for MIGRATE_CMA pageblocks. For CMA
> - * we need to make sure unallocated pages flushed from
> - * pcp lists are returned to the correct freelist.
> - */
> - set_freepage_migratetype(page, buddy_type);
> + expand(zone, page, order, current_order, area,
> + start_migratetype);
> + /*
> + * The freepage_migratetype may differ from pageblock's
> + * migratetype depending on the decisions in
> + * try_to_steal_freepages(). This is OK as long as it
> + * does not differ for MIGRATE_CMA pageblocks. For CMA
> + * we need to make sure unallocated pages flushed from
> + * pcp lists are returned to the correct freelist.
> + */
> + set_freepage_migratetype(page, start_migratetype);
>
> - trace_mm_page_alloc_extfrag(page, order, current_order,
> - start_migratetype, migratetype);
> + trace_mm_page_alloc_extfrag(page, order, current_order,
> + start_migratetype, fallback_mt);
>
> - return page;
> - }
> + return page;
> }
>
> return NULL;
>
--
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