On Wed, 2011-03-23 at 10:27 +0900, KOSAKI Motohiro wrote:

quoted

On Tue, Mar 22, 2011 at 8:08 PM, KOSAKI Motohiro
[off-list ref] wrote:

quoted

When plenty processes (eg fork bomb) are running, the TIF_MEMDIE task
never exit, at least, human feel it's never. therefore kernel become
hang-up.

"perf sched" tell us a hint.

 ------------------------------------------------------------------------------
 Task                  |   Runtime ms  | Average delay ms | Maximum delay ms |
 ------------------------------------------------------------------------------
 python:1754           |      0.197 ms | avg: 1731.727 ms | max: 3433.805 ms |
 python:1843           |      0.489 ms | avg: 1707.433 ms | max: 3622.955 ms |
 python:1715           |      0.220 ms | avg: 1707.125 ms | max: 3623.246 ms |
 python:1818           |      2.127 ms | avg: 1527.331 ms | max: 3622.553 ms |
 ...
 ...

Processes flood makes crazy scheduler delay. and then the victim process
can't run enough. Grr. Should we do?

Fortunately, we already have anti process flood framework, autogroup!
This patch reuse this framework and avoid kernel live lock.

That's cool idea but I have a concern.

You remove boosting priority in [2/5] and move victim tasks into autogroup.
If I understand autogroup right, victim process and threads in the
process take less schedule chance than now.

Right. Icky cpu-cgroup rt-runtime default enforce me to seek another solution.

I was going to mention rt, and there's s/fork/clone as well.

Today, I got private mail from Luis and he seems to have another improvement
idea. so, I might drop this patch if his one works fine.

Perhaps if TIF_MEMDIE threads needs special treatment, preemption tests
could take that into account?  (though I don't like touching fast path
for oddball cases)

	-Mike





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