linux-kernel - [PATCH] mm/page_alloc: Do not isolate redundant pageblock

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Date:   Fri, 27 Nov 2020 22:19:00 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     akpm@...ux-foundation.org
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Muchun Song <songmuchun@...edance.com>
Subject: [PATCH] mm/page_alloc: Do not isolate redundant pageblock

Current pageblock isolation logic could isolate each pageblock individually
since commit d9dddbf55667 ("mm/page_alloc: prevent merging between isolated
and other pageblocks"). So we not need to concern about page allocator
merges buddies from different pageblocks and changes MIGRATE_ISOLATE to
some other migration type.

Signed-off-by: Muchun Song <songmuchun@...edance.com>
---
 mm/page_alloc.c | 26 ++++++++------------------
 1 file changed, 8 insertions(+), 18 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index cefbef32bf4a..608a2c2b8ab7 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -8313,16 +8313,14 @@ struct page *has_unmovable_pages(struct zone *zone, struct page *page,
 }
 
 #ifdef CONFIG_CONTIG_ALLOC
-static unsigned long pfn_max_align_down(unsigned long pfn)
+static unsigned long pfn_align_down(unsigned long pfn)
 {
-	return pfn & ~(max_t(unsigned long, MAX_ORDER_NR_PAGES,
-			     pageblock_nr_pages) - 1);
+	return pfn & ~(pageblock_nr_pages - 1);
 }
 
-static unsigned long pfn_max_align_up(unsigned long pfn)
+static unsigned long pfn_align_up(unsigned long pfn)
 {
-	return ALIGN(pfn, max_t(unsigned long, MAX_ORDER_NR_PAGES,
-				pageblock_nr_pages));
+	return ALIGN(pfn, pageblock_nr_pages);
 }
 
 /* [start, end) must belong to a single zone. */
@@ -8415,14 +8413,6 @@ int alloc_contig_range(unsigned long start, unsigned long end,
 	INIT_LIST_HEAD(&cc.migratepages);
 
 	/*
-	 * What we do here is we mark all pageblocks in range as
-	 * MIGRATE_ISOLATE.  Because pageblock and max order pages may
-	 * have different sizes, and due to the way page allocator
-	 * work, we align the range to biggest of the two pages so
-	 * that page allocator won't try to merge buddies from
-	 * different pageblocks and change MIGRATE_ISOLATE to some
-	 * other migration type.
-	 *
 	 * Once the pageblocks are marked as MIGRATE_ISOLATE, we
 	 * migrate the pages from an unaligned range (ie. pages that
 	 * we are interested in).  This will put all the pages in
@@ -8438,8 +8428,8 @@ int alloc_contig_range(unsigned long start, unsigned long end,
 	 * put back to page allocator so that buddy can use them.
 	 */
 
-	ret = start_isolate_page_range(pfn_max_align_down(start),
-				       pfn_max_align_up(end), migratetype, 0);
+	ret = start_isolate_page_range(pfn_align_down(start), pfn_align_up(end),
+				       migratetype, 0);
 	if (ret)
 		return ret;
 
@@ -8522,8 +8512,8 @@ int alloc_contig_range(unsigned long start, unsigned long end,
 		free_contig_range(end, outer_end - end);
 
 done:
-	undo_isolate_page_range(pfn_max_align_down(start),
-				pfn_max_align_up(end), migratetype);
+	undo_isolate_page_range(pfn_align_down(start), pfn_align_up(end),
+				migratetype);
 	return ret;
 }
 EXPORT_SYMBOL(alloc_contig_range);
-- 
2.11.0