[CCing Mel] On Wed 26-12-12 01:27:57, Sha Zhengju wrote: > From: Sha Zhengju <handai.szj@xxxxxxxxxx> > > It's inspired by a similar optimization from Glauber Costa > (memcg: make it suck faster; https://lkml.org/lkml/2012/9/25/154). > Here we use jump label to patch the memcg page stat accounting code > in or out when not used. when the first non-root memcg comes to > life the code is patching in otherwise it is out. Mel had a workload which shown quite a big regression when memcg is enabled with no cgroups but root (it was a page fault microbench AFAIR but I do not have a link handy) so it would be nice to check how much this patch helps and what are the other places which could benefit from the static key. > Signed-off-by: Sha Zhengju <handai.szj@xxxxxxxxxx> Anyway, I like this as a first step (and the patch description should be explicit about that). See other comments bellow. > --- > include/linux/memcontrol.h | 9 +++++++++ > mm/memcontrol.c | 8 ++++++++ > 2 files changed, 17 insertions(+) > > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h > index 1d22b81..3c4430c 100644 > --- a/include/linux/memcontrol.h > +++ b/include/linux/memcontrol.h > @@ -56,6 +56,9 @@ struct mem_cgroup_reclaim_cookie { > }; > > #ifdef CONFIG_MEMCG > + > +extern struct static_key memcg_in_use_key; > + > /* > * All "charge" functions with gfp_mask should use GFP_KERNEL or > * (gfp_mask & GFP_RECLAIM_MASK). In current implementatin, memcg doesn't > @@ -158,6 +161,9 @@ extern atomic_t memcg_moving; > static inline void mem_cgroup_begin_update_page_stat(struct page *page, > bool *locked, unsigned long *flags) > { > + if (!static_key_false(&memcg_in_use_key)) > + return; Maybe static_key checks could be wrapped by a helper function with a more obvious name (mem_cgroup_in_use())? > + > if (mem_cgroup_disabled()) > return; I would assume the check ordering would be vice versa. > rcu_read_lock(); > @@ -171,6 +177,9 @@ void __mem_cgroup_end_update_page_stat(struct page *page, > static inline void mem_cgroup_end_update_page_stat(struct page *page, > bool *locked, unsigned long *flags) > { > + if (!static_key_false(&memcg_in_use_key)) > + return; > + > if (mem_cgroup_disabled()) > return; ditto > if (*locked) > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 0cb5187..a2f73d7 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -531,6 +531,8 @@ enum res_type { > #define MEM_CGROUP_RECLAIM_SHRINK_BIT 0x1 > #define MEM_CGROUP_RECLAIM_SHRINK (1 << MEM_CGROUP_RECLAIM_SHRINK_BIT) > /* * TODO comment what it is used for, please */ > +struct static_key memcg_in_use_key; > + > static void mem_cgroup_get(struct mem_cgroup *memcg); > static void mem_cgroup_put(struct mem_cgroup *memcg); > > @@ -2226,6 +2228,9 @@ void mem_cgroup_update_page_stat(struct page *page, > struct page_cgroup *pc = lookup_page_cgroup(page); > unsigned long uninitialized_var(flags); This artifact can be removed. > + if (!static_key_false(&memcg_in_use_key)) > + return; > + > if (mem_cgroup_disabled()) > return; > > @@ -6340,6 +6345,8 @@ mem_cgroup_css_alloc(struct cgroup *cont) > parent = mem_cgroup_from_cont(cont->parent); > memcg->use_hierarchy = parent->use_hierarchy; > memcg->oom_kill_disable = parent->oom_kill_disable; > + > + static_key_slow_inc(&memcg_in_use_key); Please wrap this into a function because later we will probably want to do an action depending on whether this is a first onlined group (e.g. sync stats etc...). > } > > if (parent && parent->use_hierarchy) { > @@ -6407,6 +6414,7 @@ static void mem_cgroup_css_free(struct cgroup *cont) > kmem_cgroup_destroy(memcg); > > memcg_dangling_add(memcg); > + static_key_slow_dec(&memcg_in_use_key); > mem_cgroup_put(memcg); memcg could be still alive at this moment (e.g. due to swap or kmem charges). This is not a big issue with the current state of the patch set as you ignore MEM_CGROUP_STAT_SWAP now but you shouldn't rely on that. We also have a proper place for it already (disarm_static_keys). -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>