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Date: Wed, 3 Feb 2010 12:23:05 +0530
From: Balbir Singh <balbir@...ux.vnet.ibm.com>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc: "linux-mm@...ck.org" <linux-mm@...ck.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"nishimura@....nes.nec.co.jp" <nishimura@....nes.nec.co.jp>
Subject: Re: [PATCH mmotm] memcg: use generic percpu instead of private
implementation
* KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> [2010-02-03 12:16:24]:
> This is a repost. I'll post my test program in reply to this.
> Updated against mmotm-2010-Feb-01.
>
> Thanks,
> -Kame
> ==
> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
>
> When per-cpu counter for memcg was implemneted, dynamic percpu allocator
> was not very good. But now, we have good one and useful macros.
> This patch replaces memcg's private percpu counter implementation with
> generic dynamic percpu allocator.
>
> The benefits are
> - We can remove private implementation.
> - The counters will be NUMA-aware. (Current one is not...)
> - This patch makes sizeof struct mem_cgroup smaller. Then,
> struct mem_cgroup may be fit in page size on small config.
> - About basic performance aspects, see below.
>
> [Before]
> # size mm/memcontrol.o
> text data bss dec hex filename
> 24373 2528 4132 31033 7939 mm/memcontrol.o
>
> [page-fault-throuput test on 8cpu/SMP in root cgroup]
> # /root/bin/perf stat -a -e page-faults,cache-misses --repeat 5 ./multi-fault-fork 8
>
> Performance counter stats for './multi-fault-fork 8' (5 runs):
>
> 45878618 page-faults ( +- 0.110% )
> 602635826 cache-misses ( +- 0.105% )
>
> 61.005373262 seconds time elapsed ( +- 0.004% )
>
> Then cache-miss/page fault = 13.14
>
> [After]
> #size mm/memcontrol.o
> text data bss dec hex filename
> 23913 2528 4132 30573 776d mm/memcontrol.o
> # /root/bin/perf stat -a -e page-faults,cache-misses --repeat 5 ./multi-fault-fork 8
>
> Performance counter stats for './multi-fault-fork 8' (5 runs):
>
> 48179400 page-faults ( +- 0.271% )
> 588628407 cache-misses ( +- 0.136% )
>
> 61.004615021 seconds time elapsed ( +- 0.004% )
>
> Then cache-miss/page fault = 12.22
>
> Text size is reduced.
> This performance improvement is not big and will be invisible in real world
> applications. But this result shows this patch has some good effect even
> on (small) SMP.
>
> Changelog: 2010/02/02
> - adjusted to mmotm-Feb01.
> - added performance result to the patch description.
>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> ---
> mm/memcontrol.c | 184 +++++++++++++++++++-------------------------------------
> 1 file changed, 63 insertions(+), 121 deletions(-)
>
> Index: mmotm-2.6.33-Feb01/mm/memcontrol.c
> ===================================================================
> --- mmotm-2.6.33-Feb01.orig/mm/memcontrol.c
> +++ mmotm-2.6.33-Feb01/mm/memcontrol.c
> @@ -89,54 +89,8 @@ enum mem_cgroup_stat_index {
>
> struct mem_cgroup_stat_cpu {
> s64 count[MEM_CGROUP_STAT_NSTATS];
> -} ____cacheline_aligned_in_smp;
> -
> -struct mem_cgroup_stat {
> - struct mem_cgroup_stat_cpu cpustat[0];
> };
>
> -static inline void
> -__mem_cgroup_stat_set_safe(struct mem_cgroup_stat_cpu *stat,
> - enum mem_cgroup_stat_index idx, s64 val)
> -{
> - stat->count[idx] = val;
> -}
> -
> -static inline s64
> -__mem_cgroup_stat_read_local(struct mem_cgroup_stat_cpu *stat,
> - enum mem_cgroup_stat_index idx)
> -{
> - return stat->count[idx];
> -}
> -
> -/*
> - * For accounting under irq disable, no need for increment preempt count.
> - */
> -static inline void __mem_cgroup_stat_add_safe(struct mem_cgroup_stat_cpu *stat,
> - enum mem_cgroup_stat_index idx, int val)
> -{
> - stat->count[idx] += val;
> -}
> -
> -static s64 mem_cgroup_read_stat(struct mem_cgroup_stat *stat,
> - enum mem_cgroup_stat_index idx)
> -{
> - int cpu;
> - s64 ret = 0;
> - for_each_possible_cpu(cpu)
> - ret += stat->cpustat[cpu].count[idx];
> - return ret;
> -}
> -
> -static s64 mem_cgroup_local_usage(struct mem_cgroup_stat *stat)
> -{
> - s64 ret;
> -
> - ret = mem_cgroup_read_stat(stat, MEM_CGROUP_STAT_CACHE);
> - ret += mem_cgroup_read_stat(stat, MEM_CGROUP_STAT_RSS);
> - return ret;
> -}
> -
> /*
> * per-zone information in memory controller.
> */
> @@ -270,9 +224,9 @@ struct mem_cgroup {
> unsigned long move_charge_at_immigrate;
>
> /*
> - * statistics. This must be placed at the end of memcg.
> + * percpu counter.
> */
> - struct mem_cgroup_stat stat;
> + struct mem_cgroup_stat_cpu *stat;
> };
>
> /* Stuffs for move charges at task migration. */
> @@ -441,19 +395,14 @@ mem_cgroup_remove_exceeded(struct mem_cg
> static bool mem_cgroup_soft_limit_check(struct mem_cgroup *mem)
> {
> bool ret = false;
> - int cpu;
> s64 val;
> - struct mem_cgroup_stat_cpu *cpustat;
>
> - cpu = get_cpu();
> - cpustat = &mem->stat.cpustat[cpu];
> - val = __mem_cgroup_stat_read_local(cpustat, MEM_CGROUP_STAT_SOFTLIMIT);
> + val = this_cpu_read(mem->stat->count[MEM_CGROUP_STAT_SOFTLIMIT]);
> if (unlikely(val < 0)) {
> - __mem_cgroup_stat_set_safe(cpustat, MEM_CGROUP_STAT_SOFTLIMIT,
> + this_cpu_write(mem->stat->count[MEM_CGROUP_STAT_SOFTLIMIT],
> SOFTLIMIT_EVENTS_THRESH);
> ret = true;
> }
> - put_cpu();
> return ret;
> }
>
> @@ -549,17 +498,31 @@ mem_cgroup_largest_soft_limit_node(struc
> return mz;
> }
>
> +static s64 mem_cgroup_read_stat(struct mem_cgroup *mem,
> + enum mem_cgroup_stat_index idx)
> +{
> + int cpu;
> + s64 val = 0;
> +
> + for_each_possible_cpu(cpu)
Is for_each_possible_cpu() what we need? Is this to avoid CPU hotplug
events?
Looks good overall, except the question above.
--
Balbir
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