Commit 7ad69832 authored Dec 14, 2020 by Muchun Song Committed by Linus Torvalds Dec 15, 2020

mm/page_alloc: speed 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.

We also should not be checking migratetype of buddy when "order ==
MAX_ORDER - 1" as the buddy pfn may be invalid, so adjust the condition.
With the new check, we don't need the max_order check anymore, so we
replace it.

Also adjust max_order initialization so that it's lower by one than
previously, which makes the code hopefully more clear.

Link: https://lkml.kernel.org/r/20201204155109.55451-1-songmuchun@bytedance.com


Fixes: d9dddbf5 ("mm/page_alloc: prevent merging between isolated and other pageblocks")
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 470c61d7

mm/page_alloc.c

+4 −4

Original line number	Diff line number	Diff line
		@@ -996,7 +996,7 @@ 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);
		@@ -1009,7 +1009,7 @@ 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);
		@@ -1035,7 +1035,7 @@ continue_merging:
		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
		@@ -1056,7 +1056,7 @@ continue_merging:
		is_migrate_isolate(buddy_mt)))
		goto done_merging;
		}
		max_order++;
		max_order = order + 1;
		goto continue_merging;
		}

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