Messages in this thread | | | Date | Tue, 16 Oct 2012 17:48:29 +0900 | From | Kamezawa Hiroyuki <> | Subject | Re: [PATCH v4 10/14] memcg: use static branches when code not in use |
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(2012/10/12 16:47), Glauber Costa wrote: > On 10/11/2012 05:40 PM, Michal Hocko wrote: >> On Mon 08-10-12 14:06:16, Glauber Costa wrote: >>> We can use static branches to patch the code in or out when not used. >>> >>> Because the _ACTIVE bit on kmem_accounted is only set after the >>> increment is done, we guarantee that the root memcg will always be >>> selected for kmem charges until all call sites are patched (see >>> memcg_kmem_enabled). This guarantees that no mischarges are applied. >>> >>> static branch decrement happens when the last reference count from the >>> kmem accounting in memcg dies. This will only happen when the charges >>> drop down to 0. >>> >>> When that happen, we need to disable the static branch only on those >>> memcgs that enabled it. To achieve this, we would be forced to >>> complicate the code by keeping track of which memcgs were the ones >>> that actually enabled limits, and which ones got it from its parents. >>> >>> It is a lot simpler just to do static_key_slow_inc() on every child >>> that is accounted. >>> >>> [ v4: adapted this patch to the changes in kmem_accounted ] >>> >>> Signed-off-by: Glauber Costa <glommer@parallels.com> >>> CC: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> >>> CC: Christoph Lameter <cl@linux.com> >>> CC: Pekka Enberg <penberg@cs.helsinki.fi> >>> CC: Michal Hocko <mhocko@suse.cz> >>> CC: Johannes Weiner <hannes@cmpxchg.org> >>> CC: Suleiman Souhlal <suleiman@google.com> >> >> Looks reasonable to me >> Acked-by: Michal Hocko <mhocko@suse.cz> >> >> Just a little nit. >> >> [...] >> >>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c >>> index 634c7b5..724a08b 100644 >>> --- a/mm/memcontrol.c >>> +++ b/mm/memcontrol.c >>> @@ -344,11 +344,15 @@ struct mem_cgroup { >>> /* internal only representation about the status of kmem accounting. */ >>> enum { >>> KMEM_ACCOUNTED_ACTIVE = 0, /* accounted by this cgroup itself */ >>> + KMEM_ACCOUNTED_ACTIVATED, /* static key enabled. */ >>> KMEM_ACCOUNTED_DEAD, /* dead memcg, pending kmem charges */ >>> }; >>> >>> -/* first bit */ >>> -#define KMEM_ACCOUNTED_MASK 0x1 >>> +/* >>> + * first two bits. We account when limit is on, but only after >>> + * call sites are patched >>> + */ >>> +#define KMEM_ACCOUNTED_MASK 0x3 >> >> The names are long but why not use KMEM_ACCOUNTED_ACTIVE* >> #define KMEM_ACCOUNTED_MASK 1<<KMEM_ACCOUNTED_ACTIVE | 1<<KMEM_ACCOUNTED_ACTIVATED >> > Because the names are long! =) >
please use "long" macros ;) it's not bad.
Anyway,
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
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