@@ -297,6 +297,7 @@ 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
@@ -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;
}
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 From Sioh Lee: 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 require some tricky solution to work good in all situations. Thanks. Changes: v1 -> v2: - Move xxhash() to xxhash.h/c and separate patches v2 -> v3: - Move xxhash() xxhash.c -> xxhash.h - replace xxhash_t with 'unsigned long' - update kerneldoc above xxhash() v3 -> v4: - Merge xxhash/crc32 patches - Replace crc32 with crc32c (crc32 have same as jhash2 speed) - Add auto speed test and auto choice of fastest hash function v4 -> v5: - Pickup missed xxhash patch - Update code with compile time choicen xxhash - Add more macros to make code more readable - As now that only possible use xxhash or crc32c, on crc32c allocation error, skip speed test and fallback to xxhash - For workaround too early init problem (crc32c not avaliable), move zero_checksum init to first call of fastcall() - Don't alloc page for hash testing, use arch zero pages for that v5 -> v6: - Use libcrc32c instead of CRYPTO API, mainly for code/Kconfig deps Simplification - Add crc32c_available(): libcrc32c will BUG_ON on crc32c problems, so test crc32c avaliable by crc32c_available() - Simplify choice_fastest_hash() - Simplify fasthash() - struct rmap_item && stable_node have sizeof == 64 on x86_64, that makes them cache friendly. As we don't suffer from hash collisions, change hash type from unsigned long back to u32. - Fix kbuild robot warning, make all local functions static v6 -> v7: - Drop crc32c for now and use only xxhash in ksm. v7 -> v8: - Remove empty line changes 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> CC: Andrea Arcangeli <aarcange@redhat.com> CC: linux-mm@kvack.org CC: kvm@vger.kernel.org --- mm/Kconfig | 1 + mm/ksm.c | 4 ++-- 2 files changed, 3 insertions(+), 2 deletions(-)