diff mbox series

[v3,2/3] mm/pageblock: remove false sharing in pageblock_flags

Message ID 1598928612-68996-2-git-send-email-alex.shi@linux.alibaba.com (mailing list archive)
State New, archived
Headers show
Series [v3,1/3] mm/pageblock: mitigation cmpxchg false sharing in pageblock flags | expand

Commit Message

Alex Shi Sept. 1, 2020, 2:50 a.m. UTC 
Current pageblock_flags is only 4 bits, so it has to share a char size
in cmpxchg when get set, the false sharing cause perf drop.

If we incrase the bits up to 8, false sharing would gone in cmpxchg. and
the only cost is half char per pageblock, which is half char per 128MB
on x86, 4 chars in 1 GB.

Signed-off-by: Alex Shi <alex.shi@linux.alibaba.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: linux-kernel@vger.kernel.org
Cc: linux-mm@kvack.org
---
 include/linux/pageblock-flags.h | 2 +-
 mm/page_alloc.c                 | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)
diff mbox series

Patch

diff --git a/include/linux/pageblock-flags.h b/include/linux/pageblock-flags.h
index d189441568eb..f785c9d6d68c 100644
--- a/include/linux/pageblock-flags.h
+++ b/include/linux/pageblock-flags.h
@@ -25,7 +25,7 @@  enum pageblock_bits {
 	 * Assume the bits will always align on a word. If this assumption
 	 * changes then get/set pageblock needs updating.
 	 */
-	NR_PAGEBLOCK_BITS
+	NR_PAGEBLOCK_BITS = BITS_PER_BYTE
 };
 
 #ifdef CONFIG_HUGETLB_PAGE
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 81e96d4d9c42..60342e764090 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -517,7 +517,7 @@  void set_pfnblock_flags_mask(struct page *page, unsigned long flags,
 	unsigned long bitidx, byte_bitidx;
 	unsigned char old_byte, byte;
 
-	BUILD_BUG_ON(NR_PAGEBLOCK_BITS != 4);
+	BUILD_BUG_ON(NR_PAGEBLOCK_BITS != BITS_PER_BYTE);
 	BUILD_BUG_ON(MIGRATE_TYPES > (1 << PB_migratetype_bits));
 
 	bitmap = get_pageblock_bitmap(page, pfn);