Re: [PATCH v2 1/2] mm: page_alloc: simplify pageblock migratetype check in __free_one_page().

From: Vlastimil Babka
Date: Fri Apr 01 2022 - 18:14:39 EST


On 4/1/22 20:11, Zi Yan wrote:
> From: Zi Yan <ziy@xxxxxxxxxx>
>
> Move pageblock migratetype check code in the while loop to simplify the
> logic. It also saves redundant buddy page checking code.
>
> Suggested-by: Vlastimil Babka <vbabka@xxxxxxx>
> Link: https://lore.kernel.org/linux-mm/27ff69f9-60c5-9e59-feb2-295250077551@xxxxxxx/
> Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>

Acked-by: Vlastimil Babka <vbabka@xxxxxxx>

> ---
> mm/page_alloc.c | 46 +++++++++++++++++-----------------------------
> 1 file changed, 17 insertions(+), 29 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 856473e54155..2ea106146686 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1054,7 +1054,6 @@ static inline void __free_one_page(struct page *page,
> int migratetype, fpi_t fpi_flags)
> {
> struct capture_control *capc = task_capc(zone);
> - unsigned int max_order = pageblock_order;
> unsigned long buddy_pfn;
> unsigned long combined_pfn;
> struct page *buddy;
> @@ -1070,8 +1069,7 @@ static inline void __free_one_page(struct page *page,
> VM_BUG_ON_PAGE(pfn & ((1 << order) - 1), page);
> VM_BUG_ON_PAGE(bad_range(zone, page), page);
>
> -continue_merging:
> - while (order < max_order) {
> + while (order < MAX_ORDER - 1) {
> if (compaction_capture(capc, page, order, migratetype)) {
> __mod_zone_freepage_state(zone, -(1 << order),
> migratetype);
> @@ -1082,6 +1080,22 @@ static inline void __free_one_page(struct page *page,
>
> if (!page_is_buddy(page, buddy, order))
> goto done_merging;
> +
> + if (unlikely(order >= pageblock_order)) {
> + /*
> + * We want to prevent merge between freepages on pageblock
> + * without fallbacks and normal pageblock. Without this,
> + * pageblock isolation could cause incorrect freepage or CMA
> + * accounting or HIGHATOMIC accounting.
> + */
> + int buddy_mt = get_pageblock_migratetype(buddy);
> +
> + if (migratetype != buddy_mt
> + && (!migratetype_is_mergeable(migratetype) ||
> + !migratetype_is_mergeable(buddy_mt)))
> + goto done_merging;
> + }
> +
> /*
> * Our buddy is free or it is CONFIG_DEBUG_PAGEALLOC guard page,
> * merge with it and move up one order.
> @@ -1095,32 +1109,6 @@ static inline void __free_one_page(struct page *page,
> pfn = combined_pfn;
> order++;
> }
> - if (order < MAX_ORDER - 1) {
> - /* If we are here, it means order is >= pageblock_order.
> - * We want to prevent merge between freepages on pageblock
> - * without fallbacks and normal pageblock. Without this,
> - * pageblock isolation could cause incorrect freepage or CMA
> - * accounting or HIGHATOMIC accounting.
> - *
> - * We don't want to hit this code for the more frequent
> - * low-order merging.
> - */
> - int buddy_mt;
> -
> - buddy_pfn = __find_buddy_pfn(pfn, order);
> - buddy = page + (buddy_pfn - pfn);
> -
> - if (!page_is_buddy(page, buddy, order))
> - goto done_merging;
> - buddy_mt = get_pageblock_migratetype(buddy);
> -
> - if (migratetype != buddy_mt
> - && (!migratetype_is_mergeable(migratetype) ||
> - !migratetype_is_mergeable(buddy_mt)))
> - goto done_merging;
> - max_order = order + 1;
> - goto continue_merging;
> - }
>
> done_merging:
> set_buddy_order(page, order);