Re: [BUGFIX][PATCH v6] memcg: fix percpu cached charge draining frequency
From: Ying Han
Date: Wed Jun 15 2011 - 01:30:30 EST
On Tue, Jun 14, 2011 at 6:49 PM, KAMEZAWA Hiroyuki
<kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote:
> This is a repleacement for
> memcg-fix-percpu-cached-charge-draining-frequency.patch
> +
> memcg-fix-percpu-cached-charge-draining-frequency-fix.patch
>
>
> Changelog:
> - removed unnecessary rcu_read_lock()
> - removed a fix for softlimit case (move to another independent patch)
> - make mutex static.
> - applied comment updates from Andrew Morton.
>
> A patch for softlimit will follow this.
>
> ==
> From f3f41b827d70142858ba8b370510a82d608870d0 Mon Sep 17 00:00:00 2001
> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
> Date: Wed, 15 Jun 2011 10:39:57 +0900
> Subject: [PATCH 5/6] memcg: fix behavior of per cpu charge cache draining.
>
> For performance, memory cgroup caches some "charge" from res_counter
> into per cpu cache. This works well but because it's cache,
> it needs to be flushed in some cases. Typical cases are
> 1. when someone hit limit.
> 2. when rmdir() is called and need to charges to be 0.
>
> But "1" has problem.
>
> Recently, with large SMP machines, we see many kworker runs because
> of flushing memcg's cache. Bad things in implementation are
> that even if a cpu contains a cache for memcg not related to
> a memcg which hits limit, drain code is called.
>
> This patch does
> A) check percpu cache contains a useful data or not.
> B) check other asynchronous percpu draining doesn't run.
> C) don't call local cpu callback.
>
> (*)This patch avoid changing the calling condition with hard-limit.
>
> When I run "cat 1Gfile > /dev/null" under 300M limit memcg,
>
> [Before]
> 13767 kamezawa 20 0 98.6m 424 416 D 10.0 0.0 0:00.61 cat
> 58 root 20 0 0 0 0 S 0.6 0.0 0:00.09 kworker/2:1
> 60 root 20 0 0 0 0 S 0.6 0.0 0:00.08 kworker/4:1
> 4 root 20 0 0 0 0 S 0.3 0.0 0:00.02 kworker/0:0
> 57 root 20 0 0 0 0 S 0.3 0.0 0:00.05 kworker/1:1
> 61 root 20 0 0 0 0 S 0.3 0.0 0:00.05 kworker/5:1
> 62 root 20 0 0 0 0 S 0.3 0.0 0:00.05 kworker/6:1
> 63 root 20 0 0 0 0 S 0.3 0.0 0:00.05 kworker/7:1
>
> [After]
> 2676 root 20 0 98.6m 416 416 D 9.3 0.0 0:00.87 cat
> 2626 kamezawa 20 0 15192 1312 920 R 0.3 0.0 0:00.28 top
> 1 root 20 0 19384 1496 1204 S 0.0 0.0 0:00.66 init
> 2 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kthreadd
> 3 root 20 0 0 0 0 S 0.0 0.0 0:00.00 ksoftirqd/0
> 4 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kworker/0:0
>
> Acked-by: Daisuke Nishimura <nishimura@xxxxxxxxxxxxxxxxx>
> Reviewed-by: Michal Hocko <mhocko@xxxxxxx>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
>
> Changelog:
> - removed unnecessary rcu_read_lock()
> - removed a fix for softlimit case (move to another independent patch)
> - make mutex static.
> - applied comment updates from Andrew Morton.
> ---
> mm/memcontrol.c | 54 ++++++++++++++++++++++++++++++++++++++----------------
> 1 files changed, 38 insertions(+), 16 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 915c3f3..8fb29de 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -359,7 +359,7 @@ enum charge_type {
> static void mem_cgroup_get(struct mem_cgroup *mem);
> static void mem_cgroup_put(struct mem_cgroup *mem);
> static struct mem_cgroup *parent_mem_cgroup(struct mem_cgroup *mem);
> -static void drain_all_stock_async(void);
> +static void drain_all_stock_async(struct mem_cgroup *mem);
>
> static struct mem_cgroup_per_zone *
> mem_cgroup_zoneinfo(struct mem_cgroup *mem, int nid, int zid)
> @@ -1671,7 +1671,7 @@ static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_mem,
> if (victim == root_mem) {
> loop++;
> if (loop >= 1)
> - drain_all_stock_async();
> + drain_all_stock_async(root_mem);
> if (loop >= 2) {
> /*
> * If we have not been able to reclaim
> @@ -1934,9 +1934,11 @@ struct memcg_stock_pcp {
> struct mem_cgroup *cached; /* this never be root cgroup */
> unsigned int nr_pages;
> struct work_struct work;
> + unsigned long flags;
> +#define FLUSHING_CACHED_CHARGE (0)
> };
> static DEFINE_PER_CPU(struct memcg_stock_pcp, memcg_stock);
> -static atomic_t memcg_drain_count;
> +static DEFINE_MUTEX(percpu_charge_mutex);
>
> /*
> * Try to consume stocked charge on this cpu. If success, one page is consumed
> @@ -1984,6 +1986,7 @@ static void drain_local_stock(struct work_struct *dummy)
> {
> struct memcg_stock_pcp *stock = &__get_cpu_var(memcg_stock);
> drain_stock(stock);
> + clear_bit(FLUSHING_CACHED_CHARGE, &stock->flags);
> }
>
> /*
> @@ -2008,26 +2011,45 @@ static void refill_stock(struct mem_cgroup *mem, unsigned int nr_pages)
> * expects some charges will be back to res_counter later but cannot wait for
> * it.
> */
> -static void drain_all_stock_async(void)
> +static void drain_all_stock_async(struct mem_cgroup *root_mem)
> {
> - int cpu;
> - /* This function is for scheduling "drain" in asynchronous way.
> - * The result of "drain" is not directly handled by callers. Then,
> - * if someone is calling drain, we don't have to call drain more.
> - * Anyway, WORK_STRUCT_PENDING check in queue_work_on() will catch if
> - * there is a race. We just do loose check here.
> + int cpu, curcpu;
> + /*
> + * If someone calls draining, avoid adding more kworker runs.
> */
> - if (atomic_read(&memcg_drain_count))
> + if (!mutex_trylock(&percpu_charge_mutex))
> return;
> /* Notify other cpus that system-wide "drain" is running */
> - atomic_inc(&memcg_drain_count);
> get_online_cpus();
> + /*
> + * Get a hint for avoiding draining charges on the current cpu,
> + * which must be exhausted by our charging. It is not required that
> + * this be a precise check, so we use raw_smp_processor_id() instead of
> + * getcpu()/putcpu().
> + */
> + curcpu = raw_smp_processor_id();
> for_each_online_cpu(cpu) {
> struct memcg_stock_pcp *stock = &per_cpu(memcg_stock, cpu);
> - schedule_work_on(cpu, &stock->work);
> + struct mem_cgroup *mem;
> +
> + if (cpu == curcpu)
> + continue;
> +
> + mem = stock->cached;
> + if (!mem)
> + continue;
> + if (mem != root_mem) {
> + if (!root_mem->use_hierarchy)
> + continue;
> + /* check whether "mem" is under tree of "root_mem" */
> + if (!css_is_ancestor(&mem->css, &root_mem->css))
> + continue;
> + }
> + if (!test_and_set_bit(FLUSHING_CACHED_CHARGE, &stock->flags))
> + schedule_work_on(cpu, &stock->work);
> }
> put_online_cpus();
> - atomic_dec(&memcg_drain_count);
> + mutex_unlock(&percpu_charge_mutex);
> /* We don't wait for flush_work */
> }
>
> @@ -2035,9 +2057,9 @@ static void drain_all_stock_async(void)
> static void drain_all_stock_sync(void)
> {
> /* called when force_empty is called */
> - atomic_inc(&memcg_drain_count);
> + mutex_lock(&percpu_charge_mutex);
> schedule_on_each_cpu(drain_local_stock);
> - atomic_dec(&memcg_drain_count);
> + mutex_unlock(&percpu_charge_mutex);
> }
>
> /*
> --
> 1.7.4.1
>
>
>
Tested-by: Ying Han <yinghan@xxxxxxxxxx>
--Ying
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