On 2019/08/05 20:44, Michal Hocko wrote:
>> Allowing forced charge due to being unable to invoke memcg OOM killer
>> will lead to global OOM situation, and just returning -ENOMEM will not
>> solve memcg OOM situation.
>
> Returning -ENOMEM would effectivelly lead to triggering the oom killer
> from the page fault bail out path. So effectively get us back to before
> 29ef680ae7c21110. But it is true that this is riskier from the
> observability POV when a) the OOM path wouldn't point to the culprit and
> b) it would leak ENOMEM from g-u-p path.
>
Excuse me? But according to my experiment, below code showed flood of
"Returning -ENOMEM" message instead of invoking the OOM killer.
I didn't find it gets us back to before 29ef680ae7c21110...
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1884,6 +1884,8 @@ static enum oom_status mem_cgroup_oom(struct mem_cgroup *memcg, gfp_t mask, int
mem_cgroup_unmark_under_oom(memcg);
if (mem_cgroup_out_of_memory(memcg, mask, order))
ret = OOM_SUCCESS;
+ else if (!(mask & __GFP_FS))
+ ret = OOM_SKIPPED;
else
ret = OOM_FAILED;
@@ -2457,8 +2459,10 @@ static int try_charge(struct mem_cgroup *memcg, gfp_t gfp_mask,
goto nomem;
}
nomem:
- if (!(gfp_mask & __GFP_NOFAIL))
+ if (!(gfp_mask & __GFP_NOFAIL)) {
+ printk("Returning -ENOMEM\n");
return -ENOMEM;
+ }
force:
/*
* The allocation either can't fail or will lead to more memory
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -1071,7 +1071,7 @@ bool out_of_memory(struct oom_control *oc)
* ___GFP_DIRECT_RECLAIM to get here.
*/
if (oc->gfp_mask && !(oc->gfp_mask & __GFP_FS))
- return true;
+ return !is_memcg_oom(oc);
/*
* Check if there were limitations on the allocation (only relevant for
