From a220de2af5f9abfaf553f75a774f77a7c37ef0b2 Mon Sep 17 00:00:00 2001 From: Andrew Bresticker Date: Thu, 25 Aug 2011 09:47:41 +1000 Subject: [PATCH] While back-porting Johannes Weiner's patch "mm: memcg-aware global reclaim" for an internal effort, we noticed a significant performance regression during page-reclaim heavy workloads due to high contention of the ss->id_lock. This lock protects idr map, and serializes calls to idr_get_next() in css_get_next() (which is used during the memcg hierarchy walk). Since idr_get_next() is just doing a look up, we need only serialize it with respect to idr_remove()/idr_get_new(). By making the ss->id_lock a rwlock, contention is greatly reduced and performance improves. Tested: cat a 256m file from a ramdisk in a 128m container 50 times on each core (one file + container per core) in parallel on a NUMA machine. Result is the time for the test to complete in 1 of the containers. Both kernels included Johannes' memcg-aware global reclaim patches. Before rwlock patch: 1710.778s After rwlock patch: 152.227s Signed-off-by: Andrew Bresticker Cc: Paul Menage Cc: Li Zefan Acked-by: KAMEZAWA Hiroyuki Cc: Ying Han Signed-off-by: Andrew Morton --- include/linux/cgroup.h | 2 +- kernel/cgroup.c | 18 +++++++++--------- 2 files changed, 10 insertions(+), 10 deletions(-) diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h index da7e4bc34e8c..1b7f9d525013 100644 --- a/include/linux/cgroup.h +++ b/include/linux/cgroup.h @@ -516,7 +516,7 @@ struct cgroup_subsys { struct list_head sibling; /* used when use_id == true */ struct idr idr; - spinlock_t id_lock; + rwlock_t id_lock; /* should be defined only by modular subsystems */ struct module *module; diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 1d2b6ceea95d..bc3caf0ee454 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -4880,9 +4880,9 @@ void free_css_id(struct cgroup_subsys *ss, struct cgroup_subsys_state *css) rcu_assign_pointer(id->css, NULL); rcu_assign_pointer(css->id, NULL); - spin_lock(&ss->id_lock); + write_lock(&ss->id_lock); idr_remove(&ss->idr, id->id); - spin_unlock(&ss->id_lock); + write_unlock(&ss->id_lock); kfree_rcu(id, rcu_head); } EXPORT_SYMBOL_GPL(free_css_id); @@ -4908,10 +4908,10 @@ static struct css_id *get_new_cssid(struct cgroup_subsys *ss, int depth) error = -ENOMEM; goto err_out; } - spin_lock(&ss->id_lock); + write_lock(&ss->id_lock); /* Don't use 0. allocates an ID of 1-65535 */ error = idr_get_new_above(&ss->idr, newid, 1, &myid); - spin_unlock(&ss->id_lock); + write_unlock(&ss->id_lock); /* Returns error when there are no free spaces for new ID.*/ if (error) { @@ -4926,9 +4926,9 @@ static struct css_id *get_new_cssid(struct cgroup_subsys *ss, int depth) return newid; remove_idr: error = -ENOSPC; - spin_lock(&ss->id_lock); + write_lock(&ss->id_lock); idr_remove(&ss->idr, myid); - spin_unlock(&ss->id_lock); + write_unlock(&ss->id_lock); err_out: kfree(newid); return ERR_PTR(error); @@ -4940,7 +4940,7 @@ static int __init_or_module cgroup_init_idr(struct cgroup_subsys *ss, { struct css_id *newid; - spin_lock_init(&ss->id_lock); + rwlock_init(&ss->id_lock); idr_init(&ss->idr); newid = get_new_cssid(ss, 0); @@ -5035,9 +5035,9 @@ css_get_next(struct cgroup_subsys *ss, int id, * scan next entry from bitmap(tree), tmpid is updated after * idr_get_next(). */ - spin_lock(&ss->id_lock); + read_lock(&ss->id_lock); tmp = idr_get_next(&ss->idr, &tmpid); - spin_unlock(&ss->id_lock); + read_unlock(&ss->id_lock); if (!tmp) break; -- 2.39.5