linux-kernel - [PATCH v2] mm/page_alloc: speeding up the iteration of max

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Date:   Fri,  4 Dec 2020 20:56:40 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     akpm@...ux-foundation.org, vbabka@...e.cz
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Muchun Song <songmuchun@...edance.com>
Subject: [PATCH v2] mm/page_alloc: speeding up the iteration of max_order

When we free a page whose order is very close to MAX_ORDER and greater
than pageblock_order, it wastes some CPU cycles to increase max_order
to MAX_ORDER one by one and check the pageblock migratetype of that page
repeatedly especially when MAX_ORDER is much larger than pageblock_order.

Signed-off-by: Muchun Song <songmuchun@...edance.com>
---
Changes in v2:
 - Rework the code suggested by Vlastimil. Thanks.

 mm/page_alloc.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index f91df593bf71..56e603eea1dd 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1002,7 +1002,7 @@ static inline void __free_one_page(struct page *page,
 	struct page *buddy;
 	bool to_tail;
 
-	max_order = min_t(unsigned int, MAX_ORDER, pageblock_order + 1);
+	max_order = min_t(unsigned int, MAX_ORDER - 1, pageblock_order);
 
 	VM_BUG_ON(!zone_is_initialized(zone));
 	VM_BUG_ON_PAGE(page->flags & PAGE_FLAGS_CHECK_AT_PREP, page);
@@ -1015,7 +1015,7 @@ static inline void __free_one_page(struct page *page,
 	VM_BUG_ON_PAGE(bad_range(zone, page), page);
 
 continue_merging:
-	while (order < max_order - 1) {
+	while (order < max_order) {
 		if (compaction_capture(capc, page, order, migratetype)) {
 			__mod_zone_freepage_state(zone, -(1 << order),
 								migratetype);
@@ -1041,7 +1041,7 @@ static inline void __free_one_page(struct page *page,
 		pfn = combined_pfn;
 		order++;
 	}
-	if (max_order < MAX_ORDER) {
+	if (order < MAX_ORDER - 1) {
 		/* If we are here, it means order is >= pageblock_order.
 		 * We want to prevent merge between freepages on isolate
 		 * pageblock and normal pageblock. Without this, pageblock
@@ -1062,7 +1062,7 @@ static inline void __free_one_page(struct page *page,
 						is_migrate_isolate(buddy_mt)))
 				goto done_merging;
 		}
-		max_order++;
+		max_order = order + 1;
 		goto continue_merging;
 	}
 
-- 
2.11.0