I have a few minor comments. On Wed, 8 Jun 2011 14:05:18 +0900 KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote: > This patch is made against mainline git tree. > == > From d1372da4d3c6f8051b5b1cf7b5e8b45a8094b388 Mon Sep 17 00:00:00 2001 > From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> > Date: Wed, 8 Jun 2011 13:51:11 +0900 > Subject: [BUGFIX][PATCH] 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/%d:%d when > memcg hit limit. It is because of flushing memcg's percpu cache. > Bad things in implementation are > > a) it's called before calling try_to_free_mem_cgroup_pages() > so, it's called immidiately when a task hit limit. > (I thought it was better to avoid to run into memory reclaim. > But it was wrong decision.) > > b) Even if a cpu contains a cache for memcg not related to > a memcg which hits limit, drain code is called. > > This patch fixes a) and b) by > > A) delay calling of flushing until one run of try_to_free... > Then, the number of calling is much decreased. > B) check percpu cache contains a useful data or not. > plus > C) check asynchronous percpu draining doesn't run on the cpu. > > Reported-by: Ying Han <yinghan@xxxxxxxxxx> > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> > --- > mm/memcontrol.c | 44 ++++++++++++++++++++++++++++---------------- > 1 files changed, 28 insertions(+), 16 deletions(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index bd9052a..c22c0eb 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) > @@ -1670,8 +1670,6 @@ static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_mem, > victim = mem_cgroup_select_victim(root_mem); > if (victim == root_mem) { > loop++; > - if (loop >= 1) > - drain_all_stock_async(); > if (loop >= 2) { > /* > * If we have not been able to reclaim > @@ -1723,6 +1721,7 @@ static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_mem, > return total; > } else if (mem_cgroup_margin(root_mem)) > return total; > + drain_all_stock_async(root_mem); > } > return total; > } > @@ -1934,9 +1933,11 @@ 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 ASYNC_FLUSHING (0) > }; > static DEFINE_PER_CPU(struct memcg_stock_pcp, memcg_stock); > -static atomic_t memcg_drain_count; > +static atomic_t memcg_drain_count; /* Indicates there is synchronous flusher */ > > /* > * Try to consume stocked charge on this cpu. If success, one page is consumed > @@ -1984,6 +1985,7 @@ static void drain_local_stock(struct work_struct *dummy) > { > struct memcg_stock_pcp *stock = &__get_cpu_var(memcg_stock); > drain_stock(stock); > + clear_bit(ASYNC_FLUSHING, &stock->flags); > } > > /* > @@ -2006,28 +2008,38 @@ static void refill_stock(struct mem_cgroup *mem, unsigned int nr_pages) > * Tries to drain stocked charges in other cpus. This function is asynchronous > * and just put a work per cpu for draining localy on each cpu. Caller can > * expects some charges will be back to res_counter later but cannot wait for > - * it. > + * it. This runs only when per-cpu stock contains information of memcg which > + * is under specified root_mem and no other flush runs. > */ > -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. > + > + /* > + * If synchronous flushing (which flushes all cpus's cache) runs, > + * do nothing. > */ > - if (atomic_read(&memcg_drain_count)) > + if (unlikely(atomic_read(&memcg_drain_count))) > return; > - /* Notify other cpus that system-wide "drain" is running */ > - atomic_inc(&memcg_drain_count); > get_online_cpus(); > 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; > + bool do_flush; > + > + rcu_read_lock(); Should this rcu_read_lock() be placed here ? IIUC, it's necessary only for css_is_ancestor(). > + mem = stock->cached; > + if (!mem) { > + rcu_read_unlock(); > + continue; > + } > + do_flush = ((mem == root_mem) || > + css_is_ancestor(&mem->css, &root_mem->css)); Adding "root_mem->use_hierarchy" is better to avoid flusing the cache as long as possible. Thanks, Daisuke Nishimura. > + rcu_read_unlock(); > + if (do_flush && !test_and_set_bit(ASYNC_FLUSHING, &stock->flags)) > + schedule_work_on(cpu, &stock->work); > } > put_online_cpus(); > - atomic_dec(&memcg_drain_count); > /* We don't wait for flush_work */ > } > > -- > 1.7.4.1 > > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>