Re: [PATCH 3/5] oom: oom-killer don't use proportion of system-raminternally

From: KOSAKI Motohiro
Date: Mon May 23 2011 - 22:08:12 EST

(2011/05/24 7:28), David Rientjes wrote:
On Fri, 20 May 2011, KOSAKI Motohiro wrote:

CAI Qian reported his kernel did hang-up if he ran fork intensive
workload and then invoke oom-killer.

The problem is, current oom calculation uses 0-1000 normalized value
(The unit is a permillage of system-ram). Its low precision make
a lot of same oom score. IOW, in his case, all processes have smaller
oom score than 1 and internal calculation round it to 1.

Thus oom-killer kill ineligible process. This regression is caused by
commit a63d83f427 (oom: badness heuristic rewrite).

The solution is, the internal calculation just use number of pages
instead of permillage of system-ram. And convert it to permillage
value at displaying time.

This patch doesn't change any ABI (included /proc/<pid>/oom_score_adj)
even though current logic has a lot of my dislike thing.

Same response as when you initially proposed this patch: -- you never replied to

I did replay. Why don't you read?

If you haven't understand the issue, you can apply following patch and
run it.

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index b01fa64..f35909b 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -718,6 +718,9 @@ void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask,
constraint = constrained_alloc(zonelist, gfp_mask, nodemask,
+ totalpages *= 10;
mpol_mask = (constraint == CONSTRAINT_MEMORY_POLICY) ? nodemask : NULL;
check_panic_on_oom(constraint, gfp_mask, order, mpol_mask);

The changelog doesn't accurately represent CAI Qian's problem; the issue
is that root processes are given too large of a bonus in comparison to
other threads that are using at most 1.9% of available memory. That can
be fixed, as I suggested by giving 1% bonus per 10% of memory used so that
the process would have to be using 10% before it even receives a bonus.

I already suggested an alternative patch to CAI Qian to greatly increase
the granularity of the oom score from a range of 0-1000 to 0-10000 to
differentiate between tasks within 0.01% of available memory (16MB on CAI
Qian's 16GB system). I'll propose this officially in a separate email.

This patch also includes undocumented changes such as changing the bonus
given to root processes.

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