Re: [PATCH v2] ksm: replace jhash2 with faster hash
From: Timofey Titovets
Date: Sat Dec 30 2017 - 16:28:40 EST
*FACEPALM*,
Sorry, just forgot about numbering of old jhash2 -> xxhash conversion
Also pickup patch for xxhash - arch dependent xxhash() function that will use
fastest algo for current arch.
So next will be v5, as that must be v4.
Thanks.
2017-12-29 12:52 GMT+03:00 Timofey Titovets <nefelim4ag@xxxxxxxxx>:
> Pickup, Sioh Lee crc32 patch, after some long conversation
> and hassles, merge with my work on xxhash, add
> choice fastest hash helper.
>
> Base idea are same, replace jhash2 with something faster.
>
> Perf numbers:
> Intel(R) Xeon(R) CPU E5-2420 v2 @ 2.20GHz
> ksm: crc32c hash() 12081 MB/s
> ksm: jhash2 hash() 1569 MB/s
> ksm: xxh64 hash() 8770 MB/s
> ksm: xxh32 hash() 4529 MB/s
>
> As jhash2 always will be slower, just drop it from choice.
>
> Add function to autoselect hash algo on boot, based on speed,
> like raid6 code does.
>
> Move init of zero_hash from init, to start of ksm thread,
> as ksm init run on early kernel init, run perf testing stuff on
> main kernel thread looks bad to me.
>
> One problem exists with that patch,
> ksm init run too early, and crc32c module, even compiled in
> can't be found, so i see:
> - ksm: alloc crc32c shash error 2 in dmesg.
>
> I give up on that, so ideas welcomed.
>
> Only idea that i have, are to avoid early init by moving
> zero_checksum to sysfs_store parm,
> i.e. that's default to false, and that will work, i think.
>
> Thanks.
>
> Changes:
> v1 -> v2:
> - 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
>
> 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 | 4 ++
> mm/ksm.c | 133 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++-----
> 2 files changed, 128 insertions(+), 9 deletions(-)
>
> diff --git a/mm/Kconfig b/mm/Kconfig
> index 03ff7703d322..d4fb147d4a22 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -305,6 +305,10 @@ config MMU_NOTIFIER
> config KSM
> bool "Enable KSM for page merging"
> depends on MMU
> + select XXHASH
> + select CRYPTO
> + select CRYPTO_HASH
> + select CONFIG_CRYPTO_CRC32C
> 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 be8f4576f842..fd5c9d0f7bc2 100644
> --- a/mm/ksm.c
> +++ b/mm/ksm.c
> @@ -25,7 +25,6 @@
> #include <linux/pagemap.h>
> #include <linux/rmap.h>
> #include <linux/spinlock.h>
> -#include <linux/jhash.h>
> #include <linux/delay.h>
> #include <linux/kthread.h>
> #include <linux/wait.h>
> @@ -41,6 +40,12 @@
> #include <linux/numa.h>
>
> #include <asm/tlbflush.h>
> +
> +/* Support for xxhash and crc32c */
> +#include <linux/crypto.h>
> +#include <crypto/hash.h>
> +#include <linux/xxhash.h>
> +
> #include "internal.h"
>
> #ifdef CONFIG_NUMA
> @@ -186,7 +191,7 @@ struct rmap_item {
> };
> struct mm_struct *mm;
> unsigned long address; /* + low bits used for flags below */
> - unsigned int oldchecksum; /* when unstable */
> + unsigned long oldchecksum; /* when unstable */
> union {
> struct rb_node node; /* when node of unstable tree */
> struct { /* when listed from stable tree */
> @@ -255,7 +260,7 @@ static unsigned int ksm_thread_pages_to_scan = 100;
> static unsigned int ksm_thread_sleep_millisecs = 20;
>
> /* Checksum of an empty (zeroed) page */
> -static unsigned int zero_checksum __read_mostly;
> +static unsigned long zero_checksum __read_mostly;
>
> /* Whether to merge empty (zeroed) pages with actual zero pages */
> static bool ksm_use_zero_pages __read_mostly;
> @@ -284,6 +289,115 @@ static DEFINE_SPINLOCK(ksm_mmlist_lock);
> sizeof(struct __struct), __alignof__(struct __struct),\
> (__flags), NULL)
>
> +#define CRC32C_HASH 1
> +#define XXH32_HASH 2
> +#define XXH64_HASH 3
> +
> +const static char *hash_func_names[] = { "", "crc32c", "xxh32", "xxh64" };
> +
> +static struct shash_desc desc;
> +static struct crypto_shash *tfm;
> +static uint8_t fastest_hash = 0;
> +
> +static void __init choice_fastest_hash(void)
> +{
> + void *page = kmalloc(PAGE_SIZE, GFP_KERNEL);
> + unsigned long checksum, perf, js, je;
> + unsigned long best_perf = 0;
> +
> + tfm = crypto_alloc_shash(hash_func_names[CRC32C_HASH],
> + CRYPTO_ALG_TYPE_SHASH, 0);
> +
> + if (IS_ERR(tfm)) {
> + pr_warn("ksm: alloc %s shash error %ld\n",
> + hash_func_names[CRC32C_HASH], -PTR_ERR(tfm));
> + } else {
> + desc.tfm = tfm;
> + desc.flags = 0;
> +
> + perf = 0;
> + preempt_disable();
> + js = jiffies;
> + je = js + (HZ >> 3);
> + while (time_before(jiffies, je)) {
> + crypto_shash_digest(&desc, page, PAGE_SIZE,
> + (u8 *)&checksum);
> + perf++;
> + }
> + preempt_enable();
> + if (best_perf < perf) {
> + best_perf = perf;
> + fastest_hash = CRC32C_HASH;
> + }
> + pr_info("ksm: %-8s hash() %5ld MB/s\n",
> + hash_func_names[CRC32C_HASH], perf*PAGE_SIZE >> 17);
> + }
> +
> + perf = 0;
> + preempt_disable();
> + js = jiffies;
> + je = js + (HZ >> 3);
> + while (time_before(jiffies, je)) {
> + checksum = xxh32(page, PAGE_SIZE, 0);
> + perf++;
> + }
> + preempt_enable();
> + if (best_perf < perf) {
> + best_perf = perf;
> + fastest_hash = XXH32_HASH;
> + }
> + pr_info("ksm: %-8s hash() %5ld MB/s\n",
> + hash_func_names[XXH32_HASH], perf*PAGE_SIZE >> 17);
> +
> + perf = 0;
> + preempt_disable();
> + js = jiffies;
> + je = js + (HZ >> 3);
> + while (time_before(jiffies, je)) {
> + checksum = xxh64(page, PAGE_SIZE, 0);
> + perf++;
> + }
> + preempt_enable();
> + if (best_perf < perf) {
> + best_perf = perf;
> + fastest_hash = XXH64_HASH;
> + }
> + pr_info("ksm: %-8s hash() %5ld MB/s\n",
> + hash_func_names[XXH64_HASH], perf*PAGE_SIZE >> 17);
> +
> + if (!IS_ERR(tfm) && fastest_hash != CRC32C_HASH)
> + crypto_free_shash(tfm);
> +
> + pr_info("ksm: choise %s as hash function\n",
> + hash_func_names[fastest_hash]);
> +
> + kfree(page);
> +}
> +
> +unsigned long fasthash(const void *input, size_t length)
> +{
> + unsigned long checksum = 0;
> +
> + switch (fastest_hash) {
> + case 0:
> + choice_fastest_hash();
> + checksum = fasthash(input, length);
> + break;
> + case CRC32C_HASH:
> + crypto_shash_digest(&desc, input, length,
> + (u8 *)&checksum);
> + break;
> + case XXH32_HASH:
> + checksum = xxh32(input, length, 0);
> + break;
> + case XXH64_HASH:
> + checksum = xxh64(input, length, 0);
> + break;
> + }
> +
> + return checksum;
> +}
> +
> static int __init ksm_slab_init(void)
> {
> rmap_item_cache = KSM_KMEM_CACHE(rmap_item, 0);
> @@ -982,11 +1096,11 @@ static int unmerge_and_remove_all_rmap_items(void)
> }
> #endif /* CONFIG_SYSFS */
>
> -static u32 calc_checksum(struct page *page)
> +static unsigned long calc_checksum(struct page *page)
> {
> - u32 checksum;
> + unsigned long checksum;
> void *addr = kmap_atomic(page);
> - checksum = jhash2(addr, PAGE_SIZE / 4, 17);
> + checksum = fasthash(addr, PAGE_SIZE);
> kunmap_atomic(addr);
> return checksum;
> }
> @@ -2006,7 +2120,7 @@ static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
> struct page *tree_page = NULL;
> struct stable_node *stable_node;
> struct page *kpage;
> - unsigned int checksum;
> + unsigned long checksum;
> int err;
> bool max_page_sharing_bypass = false;
>
> @@ -2336,6 +2450,9 @@ static int ksm_scan_thread(void *nothing)
> set_freezable();
> set_user_nice(current, 5);
>
> + /* The correct value depends on page size and endianness */
> + zero_checksum = calc_checksum(ZERO_PAGE(0));
> +
> while (!kthread_should_stop()) {
> mutex_lock(&ksm_thread_mutex);
> wait_while_offlining();
> @@ -3068,8 +3185,6 @@ static int __init ksm_init(void)
> struct task_struct *ksm_thread;
> int err;
>
> - /* The correct value depends on page size and endianness */
> - zero_checksum = calc_checksum(ZERO_PAGE(0));
> /* Default to false for backwards compatibility */
> ksm_use_zero_pages = false;
>
> --
> 2.15.1
--
Have a nice day,
Timofey.