Re: [PATCH v4 10/14] memcg: use static branches when code not in use
From: Michal Hocko <hidden>
Date: 2012-10-11 13:40:34
Also in:
linux-mm, lkml
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 <redacted> CC: Kamezawa Hiroyuki <redacted> CC: Christoph Lameter <redacted> CC: Pekka Enberg <penberg-bbCR+/B0CizivPeTLB3BmA@public.gmane.org> CC: Michal Hocko <redacted> CC: Johannes Weiner <redacted> CC: Suleiman Souhlal <redacted>
Looks reasonable to me Acked-by: Michal Hocko <redacted> Just a little nit. [...]
quoted hunk ↗ jump to hunk
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 [...] -- Michal Hocko SUSE Labs