Re: [PATCH v2 2/2] mm: memcontrol: make cgroup_memory_noswap a static key

Muchun Song
2022-09-20T02:43:04Z

> On Sep 20, 2022, at 02:06, Kairui Song <ryncsn-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>
> From: Kairui Song <kasong-1Nz4purKYjRBDgjK7y7TUQ@public.gmane.org>
>
> 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-IBi9RG/b67k@public.gmane.org>
> Signed-off-by: Kairui Song <kasong-1Nz4purKYjRBDgjK7y7TUQ@public.gmane.org>

Acked-by: Muchun Song <songmuchun-EC8Uxl6Npydl57MIdRCFDg@public.gmane.org>

Thanks.