[PATCH 0/2] memcg: fix oom handling

[KAMEZAWA Hiroyuki]

Li Zefan reported

(a) This goes dead lock:
==
   #echo 0 >  (...)/01/memory.limit_in_bytes   #set memcg's limit to 0,
   #echo $$ > (...)/01/memory.tasks            #move task
   # do something...
==

(b) seems to be dead lock
==
   #echo 40k >  (...)/01/memory.limit_in_bytes   #set memcg's limit to 0,
   #echo $$ > (...)/01/memory.tasks            #move task
   # do something...
==


I think (a) is BUG. (b) is just slow down.
(you can see pgpgin/pgpgout count is increasing in (B).)

This patch set is for handling (a). Li-san, could you check ?
This works well in my environment.(means OOM-Killer is called in proper way.)

 [1/2].... current mmotm has pagefault_out_of_memory() but this doesn't consider
           memcg. When memcg hit limits in page_fault and panic_on_oom is set,
           the kernel panics.
           This tries to fix that.
           (See patches/mm-invoke-oom-killer-from-page-fault.patch)

 [2/2].... fixes wrong logic of check_under_limit.

Anyway, it seems hierarchy support is *not* enough in OOM handler.
Balbir, could you check it ? 
I think "a bad process in hierarchy rather than memcg" should be killed.

Thanks,
-Kame

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