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: http://lkml.kernel.org/r/20181023182554.23464-3-nefelim4ag@gmail.com
Signed-off-by: Timofey Titovets <nefelim4ag@gmail.com>
Signed-off-by: leesioh <solee@os.korea.ac.kr>
Reviewed-by: Pavel Tatashin <pavel.tatashin@microsoft.com>
Reviewed-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/Kconfig b/mm/Kconfig
index d85e39da47aed166d58f7bba669d60afb12bad59..25c71eb8a7dbd9170f29cdbca9d273d02afb1cf3 100644 (file)
--- 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
        help
          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 5b0894b45ee57257f34bde6072ae63a26c1714e6..1a088306ef817dcbd643729f394fd25c037655dd 100644 (file)
--- 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);
        kunmap_atomic(addr);
        return checksum;
 }