[Devel] [PATCH rh7 1/2] memcg: do not ignore oom_guarantee for unlimited cgroups

[Vladimir Davydov]

We should take into account memory.oom_guarantee even for unlimited
cgroups in order to handle system slices and VM cgroups properly. Since
we have no idea of what VM's limit is actually equal to, let's rework
the formula behind the worst cgroup selection. Instead of using

  (usage - guarantee) / (limit - guarantee)

let's just take

  usage / guarantee

This looks reasonable - the more cgroup exceeds its guarantee the sooner
it will be selected by OOM killer. Note, after this change containers
w/o guarantee configured will be primary OOM victims, but that looks
fair enough. Among such containers, the one with the greatest memory
consumption value will be selected, which is also fine.

https://jira.sw.ru/browse/PSBM-44683

Signed-off-by: Vladimir Davydov <vdavydov at virtuozzo.com>
---
 mm/memcontrol.c | 14 +++++---------
 1 file changed, 5 insertions(+), 9 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 6009ff5d1903..af39f25df67f 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1702,18 +1702,14 @@ struct oom_context *mem_cgroup_oom_context(struct mem_cgroup *memcg)
 
 unsigned long mem_cgroup_overdraft(struct mem_cgroup *memcg)
 {
-	unsigned long long guarantee, limit, usage;
-	unsigned long score;
+	unsigned long long guarantee, usage;
 
-	guarantee = ACCESS_ONCE(memcg->oom_guarantee);
-	limit = res_counter_read_u64(&memcg->memsw, RES_LIMIT);
-	usage = res_counter_read_u64(&memcg->memsw, RES_USAGE);
-
-	if (limit >= RESOURCE_MAX || guarantee >= limit || usage <= guarantee)
+	if (mem_cgroup_is_root(memcg))
 		return 0;
 
-	score = div64_u64(1000 * (usage - guarantee), limit - guarantee);
-	return score > 0 ? score : 1;
+	guarantee = ACCESS_ONCE(memcg->oom_guarantee);
+	usage = res_counter_read_u64(&memcg->memsw, RES_USAGE);
+	return div64_u64(1000 * usage, guarantee + 1);
 }
 
 unsigned long mem_cgroup_total_pages(struct mem_cgroup *memcg, bool swap)
-- 
2.1.4