Commit 59e1a2f4 authored Dec 28, 2018 by Timofey Titovets Committed by Linus Torvalds Dec 28, 2018

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>

parent 0b9df58b

mm/Kconfig

+1 −0

Original line number	Diff line number	Diff line
		@@ -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

mm/ksm.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -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;
		}

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