path: root/mm
diff options
authorTimofey Titovets <>2018-12-28 00:34:05 -0800
committerLinus Torvalds <>2018-12-28 12:11:46 -0800
commit59e1a2f4bf83744e748636415fde7d1e9f557e05 (patch)
treecc25e2343b4d9be364d9fbd04de37a7326d796cd /mm
parent0b9df58b79fa283fbedc0fb6a8e248599444bacc (diff)
ksm: replace jhash2 with xxhash
Replace jhash2 with xxhash. Perf numbers: Intel(R) Xeon(R) CPU E5-2420 v2 @ 2.20GHz ksm: crc32c hash() 12081 MB/s ksm: xxh64 hash() 8770 MB/s ksm: xxh32 hash() 4529 MB/s ksm: jhash2 hash() 1569 MB/s Sioh Lee did some testing: crc32c_intel: 1084.10ns crc32c (no hardware acceleration): 7012.51ns xxhash32: 2227.75ns xxhash64: 1413.16ns jhash2: 5128.30ns As jhash2 always will be slower (for data size like PAGE_SIZE). Don't use it in ksm at all. Use only xxhash for now, because for using crc32c, cryptoapi must be initialized first - that requires some tricky solution to work well in all situations. Link: Signed-off-by: Timofey Titovets <> Signed-off-by: leesioh <> Reviewed-by: Pavel Tatashin <> Reviewed-by: Mike Rapoport <> Reviewed-by: Andrew Morton <> Cc: Andrea Arcangeli <> Signed-off-by: Andrew Morton <> Signed-off-by: Linus Torvalds <>
Diffstat (limited to 'mm')
2 files changed, 3 insertions, 2 deletions
diff --git a/mm/Kconfig b/mm/Kconfig
index d85e39da47ae..25c71eb8a7db 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -291,6 +291,7 @@ config MMU_NOTIFIER
config KSM
bool "Enable KSM for page merging"
depends on MMU
+ select XXHASH
Enable Kernel Samepage Merging: KSM periodically scans those areas
of an application's address space that an app has advised may be
diff --git a/mm/ksm.c b/mm/ksm.c
index 5b0894b45ee5..1a088306ef81 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -25,7 +25,7 @@
#include <linux/pagemap.h>
#include <linux/rmap.h>
#include <linux/spinlock.h>
-#include <linux/jhash.h>
+#include <linux/xxhash.h>
#include <linux/delay.h>
#include <linux/kthread.h>
#include <linux/wait.h>
@@ -1009,7 +1009,7 @@ static u32 calc_checksum(struct page *page)
u32 checksum;
void *addr = kmap_atomic(page);
- checksum = jhash2(addr, PAGE_SIZE / 4, 17);
+ checksum = xxhash(addr, PAGE_SIZE, 0);
return checksum;