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Date:   Mon, 19 Sep 2022 19:29:02 -0700
From:   Roman Gushchin <roman.gushchin@linux.dev>
To:     Kairui Song <kasong@tencent.com>
Cc:     cgroups@vger.kernel.org, linux-mm@kvack.org,
        Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@kernel.org>,
        Shakeel Butt <shakeelb@google.com>,
        Muchun Song <songmuchun@bytedance.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-kernel@vger.kernel.org, Michal Hocko <mhocko@suse.com>
Subject: Re: [PATCH v2 2/2] mm: memcontrol: make cgroup_memory_noswap a
 static key
Message-ID: <YyklbsFFu26cmHPU@P9FQF9L96D>
References: <20220919180634.45958-1-ryncsn@gmail.com>
 <20220919180634.45958-3-ryncsn@gmail.com>
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On Tue, Sep 20, 2022 at 02:06:34AM +0800, Kairui Song wrote:
> From: Kairui Song <kasong@tencent.com>
> 
> cgroup_memory_noswap is used in many hot path, so make it a static key
> to lower the kernel overhead.
> 
> Using 8G of ZRAM as SWAP, benchmark using `perf stat -d -d -d --repeat 100`
> with the following code snip in a non-root cgroup:
> 
>    #include <stdio.h>
>    #include <string.h>
>    #include <linux/mman.h>
>    #include <sys/mman.h>
>    #define MB 1024UL * 1024UL
>    int main(int argc, char **argv){
>       void *p = mmap(NULL, 8000 * MB, PROT_READ | PROT_WRITE,
>                      MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
>       memset(p, 0xff, 8000 * MB);
>       madvise(p, 8000 * MB, MADV_PAGEOUT);
>       memset(p, 0xff, 8000 * MB);
>       return 0;
>    }
> 
> Before:
>           7,021.43 msec task-clock                #    0.967 CPUs utilized            ( +-  0.03% )
>              4,010      context-switches          #  573.853 /sec                     ( +-  0.01% )
>                  0      cpu-migrations            #    0.000 /sec
>          2,052,057      page-faults               #  293.661 K/sec                    ( +-  0.00% )
>     12,616,546,027      cycles                    #    1.805 GHz                      ( +-  0.06% )  (39.92%)
>        156,823,666      stalled-cycles-frontend   #    1.25% frontend cycles idle     ( +-  0.10% )  (40.25%)
>        310,130,812      stalled-cycles-backend    #    2.47% backend cycles idle      ( +-  4.39% )  (40.73%)
>     18,692,516,591      instructions              #    1.49  insn per cycle
>                                                   #    0.01  stalled cycles per insn  ( +-  0.04% )  (40.75%)
>      4,907,447,976      branches                  #  702.283 M/sec                    ( +-  0.05% )  (40.30%)
>         13,002,578      branch-misses             #    0.26% of all branches          ( +-  0.08% )  (40.48%)
>      7,069,786,296      L1-dcache-loads           #    1.012 G/sec                    ( +-  0.03% )  (40.32%)
>        649,385,847      L1-dcache-load-misses     #    9.13% of all L1-dcache accesses  ( +-  0.07% )  (40.10%)
>      1,485,448,688      L1-icache-loads           #  212.576 M/sec                    ( +-  0.15% )  (39.49%)
>         31,628,457      L1-icache-load-misses     #    2.13% of all L1-icache accesses  ( +-  0.40% )  (39.57%)
>          6,667,311      dTLB-loads                #  954.129 K/sec                    ( +-  0.21% )  (39.50%)
>          5,668,555      dTLB-load-misses          #   86.40% of all dTLB cache accesses  ( +-  0.12% )  (39.03%)
>                765      iTLB-loads                #  109.476 /sec                     ( +- 21.81% )  (39.44%)
>          4,370,351      iTLB-load-misses          # 214320.09% of all iTLB cache accesses  ( +-  1.44% )  (39.86%)
>        149,207,254      L1-dcache-prefetches      #   21.352 M/sec                    ( +-  0.13% )  (40.27%)
> 
>            7.25869 +- 0.00203 seconds time elapsed  ( +-  0.03% )
> 
> After:
>           6,576.16 msec task-clock                #    0.953 CPUs utilized            ( +-  0.10% )
>              4,020      context-switches          #  605.595 /sec                     ( +-  0.01% )
>                  0      cpu-migrations            #    0.000 /sec
>          2,052,056      page-faults               #  309.133 K/sec                    ( +-  0.00% )
>     11,967,619,180      cycles                    #    1.803 GHz                      ( +-  0.36% )  (38.76%)
>        161,259,240      stalled-cycles-frontend   #    1.38% frontend cycles idle     ( +-  0.27% )  (36.58%)
>        253,605,302      stalled-cycles-backend    #    2.16% backend cycles idle      ( +-  4.45% )  (34.78%)
>     19,328,171,892      instructions              #    1.65  insn per cycle
>                                                   #    0.01  stalled cycles per insn  ( +-  0.10% )  (31.46%)
>      5,213,967,902      branches                  #  785.461 M/sec                    ( +-  0.18% )  (30.68%)
>         12,385,170      branch-misses             #    0.24% of all branches          ( +-  0.26% )  (34.13%)
>      7,271,687,822      L1-dcache-loads           #    1.095 G/sec                    ( +-  0.12% )  (35.29%)
>        649,873,045      L1-dcache-load-misses     #    8.93% of all L1-dcache accesses  ( +-  0.11% )  (41.41%)
>      1,950,037,608      L1-icache-loads           #  293.764 M/sec                    ( +-  0.33% )  (43.11%)
>         31,365,566      L1-icache-load-misses     #    1.62% of all L1-icache accesses  ( +-  0.39% )  (45.89%)
>          6,767,809      dTLB-loads                #    1.020 M/sec                    ( +-  0.47% )  (48.42%)
>          6,339,590      dTLB-load-misses          #   95.43% of all dTLB cache accesses  ( +-  0.50% )  (46.60%)
>                736      iTLB-loads                #  110.875 /sec                     ( +-  1.79% )  (48.60%)
>          4,314,836      iTLB-load-misses          # 518653.73% of all iTLB cache accesses  ( +-  0.63% )  (42.91%)
>        144,950,156      L1-dcache-prefetches      #   21.836 M/sec                    ( +-  0.37% )  (41.39%)
> 
>            6.89935 +- 0.00703 seconds time elapsed  ( +-  0.10% )
> 
> The performance is clearly better. There is no significant hotspot
> improvement according to perf report, as there are quite a few
> callers of memcg_swap_enabled and do_memsw_account (which calls
> memcg_swap_enabled). Many pieces of minor optimizations resulted
> in lower overhead for the branch predictor, and bettter performance.
> 
> Acked-by: Michal Hocko <mhocko@suse.com>
> Signed-off-by: Kairui Song <kasong@tencent.com>

Acked-by: Roman Gushchin <roman.gushchin@linux.dev>

Thanks!