linux-kernel - Re: [PATCH v3] oom-kill: add lowmem usage aware oom kill handling

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Message-ID: <f8c9aca9c98db8ae7df3ac2d7ac8d922.squirrel@webmail-b.css.fujitsu.com>
Date:	Sat, 30 Jan 2010 01:11:17 +0900 (JST)
From:	"KAMEZAWA Hiroyuki" <kamezawa.hiroyu@...fujitsu.com>
To:	"Alan Cox" <alan@...rguk.ukuu.org.uk>
Cc:	vedran.furac@...il.com,
	"KAMEZAWA Hiroyuki" <kamezawa.hiroyu@...fujitsu.com>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>, rientjes@...gle.com,
	minchan.kim@...il.com,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"balbir@...ux.vnet.ibm.com" <balbir@...ux.vnet.ibm.com>
Subject: Re: [PATCH v3] oom-kill: add lowmem usage aware oom kill handling

Alan Cox wrote:
>> off by default. Problem is that it breaks java and some other stuff that
>> allocates much more memory than it needs. Very quickly Committed_AS hits
>> CommitLimit and one cannot allocate any more while there is plenty of
>> memory still unused.
>
> So how about you go and have a complain at the people who are causing
> your problem, rather than the kernel.
>
Alan, please allow me to talk about my concern.

At first, I think all OOM-killer are bad and there are no chance
to implement innocent, good OOM-Killer. The best way we can do is
"never cause OOM-Kill". But we're human being, OOM-Killer can happen
by _mistake_....

For example, a customer runs 1000+ process of Oracle without using
HugeTLB and the total size of page table goes up to 10GByes. Hahaha.
(Of course, We asked him  to use Hugetlb ;) We can't ask him to
 use overcommit memory if much proprietaty applications runs on it.)

So, I believe there is a cirtial situation OOM-Killer has to run even
if it's bad. Even in corner case.
Now, in OOM situaion, sshd or X-server or some task launcher is killed at
first if oom_adj is not tweaked. IIUC, OOM-Killer is for giving a chance
to administrator to recover his system, safe reboot. But if sshd/X is
kiiled, this is no help.

My first purpose was to prevent killing some daemons or task launchers.
The first patch was nacked ;).

On that way, I tried to add lowmem counting because it was also
my concern. This was nacked ;(

I stop this because of my personal reason. For my enviroment,
panic_on_oom=1 works enough well.For Vedran's, overcommit memory will work
well. But oom-killer kills very bad process if not tweaked.
So, I think some improvement should be done.

And we have memcg even if it's called as ugly workaround.
Sorry for all the noise.

Bye,
-Kame

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