Re: [PATCH v2 1/2] mm: use aligned address in clear_gigantic_page()

Kefeng Wang
2024-11-01T07:44:06Z

On 2024/10/31 16:39, Huang, Ying wrote:
> Kefeng Wang <wangkefeng.wang@huawei.com> writes:
>
> [snip]
>>
>>>> 1) Will test some rand test to check the different of performance as
>>>> David suggested.>>>>
>>>> 2) Hope the LKP to run more tests since it is very useful(more test
>>>> set and different machines)
>>> I'm starting to use LKP to test.
>>
>> Greet.

Sorry for the late,

>
> I have run some tests with LKP to test.
>
> Firstly, there's almost no measurable difference between clearing pages
> from start to end or from end to start on Intel server CPU. I guess
> that there's some similar optimization for both direction.
>
> For multiple processes (same as logical CPU number)
> vm-scalability/anon-w-seq test case, the benchmark score increases
> about 22.4%.

So process_huge_page is better than clear_gigantic_page() on Intel?

Could you test the following case on x86?
echo 10240 >
/sys/devices/system/node/node0/hugepages/hugepages-2048kB/nr_hugepages
mkdir -p /hugetlbfs/
mount none /hugetlbfs/ -t hugetlbfs
rm -f /hugetlbfs/test && fallocate -l 20G /hugetlbfs/test && fallocate
-d -l 20G /hugetlbfs/test && time taskset -c 10 fallocate -l 20G
/hugetlbfs/test

>
> For multiple processes vm-scalability/anon-w-rand test case, no
> measurable difference for benchmark score.
>
> So, the optimization helps sequential workload mainly.
>
> In summary, on x86, process_huge_page() will not introduce any
> regression. And it helps some workload.
>
> However, on ARM64, it does introduce some regression for clearing pages
> from end to start. That needs to be addressed. I guess that the
> regression can be resolved via using more clearing from start to end
> (but not all). For example, can you take a look at the patch below?
> Which uses the similar framework as before, but clear each small trunk
> (mpage) from start to end. You can adjust MPAGE_NRPAGES to check when
> the regression can be restored.
>
> WARNING: the patch is only build tested.

Base: baseline
Change1: using clear_gigantic_page() for 2M PMD
Change2: your patch with MPAGE_NRPAGES=16
Change3: Case3 + fix[1]
Change4: your patch with MPAGE_NRPAGES=64 + fix[1]

1. For rand write,
case-anon-w-rand/case-anon-w-rand-hugetlb no measurable difference

2. For seq write,

1) case-anon-w-seq-mt:
base:
real 0m2.490s 0m2.254s 0m2.272s
user 1m59.980s 2m23.431s 2m18.739s
sys 1m3.675s 1m15.462s 1m15.030s

Change1:
real 0m2.234s 0m2.225s 0m2.159s
user 2m56.105s 2m57.117s 3m0.489s
sys 0m17.064s 0m17.564s 0m16.150s

Change2：
real 0m2.244s 0m2.384s 0m2.370s
user 2m39.413s 2m41.990s 2m42.229s
sys 0m19.826s 0m18.491s 0m18.053s

Change3： // best performance
real 0m2.155s 0m2.204s 0m2.194s
user 3m2.640s 2m55.837s 3m0.902s
sys 0m17.346s 0m17.630s 0m18.197s

Change4：
real 0m2.287s 0m2.377s 0m2.284s
user 2m37.030s 2m52.868s 3m17.593s
sys 0m15.445s 0m34.430s 0m45.224s

2) case-anon-w-seq-hugetlb
very similar 1), Change4 slightly better than Change3, but not big
different.

3) hugetlbfs fallocate 20G
Change1(0m1.136s) = Change3(0m1.136s) = Change4(0m1.135s) <
Change2(0m1.275s) < base(0m3.016s)

In summary, the Change3 is best and Change1 is good on my arm64 machine.

>
> Best Regards,
> Huang, Ying
>
> -----------------------------------8<----------------------------------------
> From 406bcd1603987fdd7130d2df6f7d4aee4cc6b978 Mon Sep 17 00:00:00 2001
> From: Huang Ying <ying.huang@intel.com>
> Date: Thu, 31 Oct 2024 11:13:57 +0800
> Subject: [PATCH] mpage clear
>
> ---
> mm/memory.c | 70 ++++++++++++++++++++++++++++++++++++++++++++++++++---
> 1 file changed, 67 insertions(+), 3 deletions(-)
>
> diff --git a/mm/memory.c b/mm/memory.c
> index 3ccee51adfbb..1fdc548c4275 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -6769,6 +6769,68 @@ static inline int process_huge_page(
> return 0;
> }
>
> +#define MPAGE_NRPAGES (1<<4)
> +#define MPAGE_SIZE (PAGE_SIZE * MPAGE_NRPAGES)
> +static inline int clear_huge_page(
> + unsigned long addr_hint, unsigned int nr_pages,
> + int (*process_subpage)(unsigned long addr, int idx, void *arg),
> + void *arg)
> +{
> + int i, n, base, l, ret;
> + unsigned long addr = addr_hint &
> + ~(((unsigned long)nr_pages << PAGE_SHIFT) - 1);
> + unsigned long nr_mpages = ((unsigned long)nr_pages << PAGE_SHIFT) / MPAGE_SIZE;
> +
> + /* Process target subpage last to keep its cache lines hot */
> + might_sleep();
> + n = (addr_hint - addr) / MPAGE_SIZE;
> + if (2 * n <= nr_mpages) {
> + /* If target subpage in first half of huge page */
> + base = 0;
> + l = n;
> + /* Process subpages at the end of huge page */
> + for (i = nr_mpages - 1; i >= 2 * n; i--) {
> + cond_resched();
> + ret = process_subpage(addr + i * MPAGE_SIZE,
> + i * MPAGE_NRPAGES, arg);
> + if (ret)
> + return ret;
> + }
> + } else {
> + /* If target subpage in second half of huge page */
> + base = nr_mpages - 2 * (nr_mpages - n);
> + l = nr_mpages - n;
> + /* Process subpages at the begin of huge page */
> + for (i = 0; i < base; i++) {
> + cond_resched();
> + ret = process_subpage(addr + i * MPAGE_SIZE,
> + i * MPAGE_NRPAGES, arg);
> + if (ret)
> + return ret;
> + }
> + }
> + /*
> + * Process remaining subpages in left-right-left-right pattern
> + * towards the target subpage
> + */
> + for (i = 0; i < l; i++) {
> + int left_idx = base + i;
> + int right_idx = base + 2 * l - 1 - i;
> +
> + cond_resched();
> + ret = process_subpage(addr + left_idx * MPAGE_SIZE,
> + left_idx * MPAGE_NRPAGES, arg);
> + if (ret)
> + return ret;
> + cond_resched();
> + ret = process_subpage(addr + right_idx * MPAGE_SIZE,
> + right_idx * MPAGE_NRPAGES, arg);
> + if (ret)
> + return ret;
> + }
> + return 0;
> +}
> +
> static void clear_gigantic_page(struct folio *folio, unsigned long addr,
> unsigned int nr_pages)
> {
> @@ -6784,8 +6846,10 @@ static void clear_gigantic_page(struct folio *folio, unsigned long addr,
> static int clear_subpage(unsigned long addr, int idx, void *arg)
> {
> struct folio *folio = arg;
> + int i;
>
> - clear_user_highpage(folio_page(folio, idx), addr);
> + for (i = 0; i < MPAGE_NRPAGES; i++)
> + clear_user_highpage(folio_page(folio, idx + i), addr + i * PAGE_SIZE);
> return 0;
> }
>
> @@ -6798,10 +6862,10 @@ void folio_zero_user(struct folio *folio, unsigned long addr_hint)
> {
> unsigned int nr_pages = folio_nr_pages(folio);
>
> - if (unlikely(nr_pages > MAX_ORDER_NR_PAGES))
> + if (unlikely(nr_pages != HPAGE_PMD_NR))
> clear_gigantic_page(folio, addr_hint, nr_pages);
> else
> - process_huge_page(addr_hint, nr_pages, clear_subpage, folio);
> + clear_huge_page(addr_hint, nr_pages, clear_subpage, folio);
> }
>
> static int copy_user_gigantic_page(struct folio *dst, struct folio *src,

[1] fix patch

diff --git a/mm/memory.c b/mm/memory.c
index b22d4b83295b..aee99ede0c4f 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -6816,7 +6816,7 @@ static inline int clear_huge_page(
base = 0;
l = n;
/* Process subpages at the end of huge page */
- for (i = nr_mpages - 1; i >= 2 * n; i--) {
+ for (i = 2 * n; i < nr_mpages; i++) {
cond_resched();
ret = process_subpage(addr + i * MPAGE_SIZE,
i * MPAGE_NRPAGES, arg);