From: Timofey Titovets <nefelim4ag@xxxxxxxxx>
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
By sioh Lee tests (copy from other mail):
Test platform: openstack cloud platform (NEWTON version)
Experiment node: openstack based cloud compute node (CPU: xeon E5-2620 v3, memory 64gb)
VM: (2 VCPU, RAM 4GB, DISK 20GB) * 4
Linux kernel: 4.14 (latest version)
KSM setup - sleep_millisecs: 200ms, pages_to_scan: 200
Experiment process
Firstly, we turn off KSM and launch 4 VMs.
Then we turn on the KSM and measure the checksum computation time until full_scans become two.
The experimental results (the experimental value is the average of the measured values)
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.
Signed-off-by: Timofey Titovets <nefelim4ag@xxxxxxxxx>
Signed-off-by: leesioh <solee@xxxxxxxxxxxxxx>
CC: Andrea Arcangeli <aarcange@xxxxxxxxxx>
CC: linux-mm@xxxxxxxxx
CC: kvm@xxxxxxxxxxxxxxx
---
mm/Kconfig | 1 +
mm/ksm.c | 6 ++++--
2 files changed, 5 insertions(+), 2 deletions(-)
diff --git a/mm/Kconfig b/mm/Kconfig
index a550635ea5c3..b5f923081bce 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -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
diff --git a/mm/ksm.c b/mm/ksm.c
index 5b0894b45ee5..30c595dd5d87 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>
@@ -41,6 +41,7 @@
#include <linux/numa.h>
#include <asm/tlbflush.h>
+
#include "internal.h"
#ifdef CONFIG_NUMA
@@ -303,6 +304,7 @@ static DEFINE_SPINLOCK(ksm_mmlist_lock);
sizeof(struct __struct), __alignof__(struct __struct),\
(__flags), NULL)
+
static int __init ksm_slab_init(void)
{
rmap_item_cache = KSM_KMEM_CACHE(rmap_item, 0);
@@ -1009,7 +1011,7 @@ 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;
}
--
2.19.0
