From: Timofey Titovets <nefelim4ag@xxxxxxxxx> Subject: 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@xxxxxxxxx Signed-off-by: Timofey Titovets <nefelim4ag@xxxxxxxxx> Signed-off-by: leesioh <solee@xxxxxxxxxxxxxx> Reviewed-by: Pavel Tatashin <pavel.tatashin@xxxxxxxxxxxxx> Reviewed-by: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx> Reviewed-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- --- a/mm/Kconfig~ksm-replace-jhash2-with-xxhash +++ a/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 --- a/mm/ksm.c~ksm-replace-jhash2-with-xxhash +++ a/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 *pa { 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; } _
