On 9/13/18 5:19 PM, Timofey Titovets wrote:
> 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"
Please remove this change
>
> #ifdef CONFIG_NUMA
> @@ -303,6 +304,7 @@ static DEFINE_SPINLOCK(ksm_mmlist_lock);
> sizeof(struct __struct), __alignof__(struct __struct),\
> (__flags), NULL)
>
> +
And this one
> 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;
> }
>
