linux-kernel - Re: [PATCH v2] virtio_balloon: disable oom killer when fill balloon

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Date:	Wed, 27 Apr 2011 10:22:24 +0800
From:	Dave Young <hidave.darkstar@...il.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	Minchan Kim <minchan.kim@...il.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-mm <linux-mm@...ck.org>
Subject: Re: [PATCH v2] virtio_balloon: disable oom killer when fill balloon

On Wed, Apr 27, 2011 at 10:06 AM, KOSAKI Motohiro
<kosaki.motohiro@...fujitsu.com> wrote:
>> On Wed, Apr 27, 2011 at 9:37 AM, Dave Young <hidave.darkstar@...il.com> wrote:
>> > On Wed, Apr 27, 2011 at 7:33 AM, Minchan Kim <minchan.kim@...il.com> wrote:
>> >> On Tue, Apr 26, 2011 at 6:39 PM, Dave Young <hidave.darkstar@...il.com> wrote:
>> >>> On Tue, Apr 26, 2011 at 5:28 PM, Minchan Kim <minchan.kim@...il.com> wrote:
>> >>>> Please resend this with [2/2] to linux-mm.
>> >>>>
>> >>>> On Tue, Apr 26, 2011 at 5:59 PM, Dave Young <hidave.darkstar@...il.com> wrote:
>> >>>>> When memory pressure is high, virtio ballooning will probably cause oom killing.
>> >>>>> Even if alloc_page with GFP_NORETRY itself does not directly trigger oom it
>> >>>>> will make memory becoming low then memory alloc of other processes will trigger
>> >>>>> oom killing. It is not desired behaviour.
>> >>>>
>> >>>> I can't understand why it is undesirable.
>> >>>> Why do we have to handle it specially?
>> >>>>
>> >>>
>> >>> Suppose user run some random memory hogging process while ballooning
>> >>> it will be undesirable.
>> >>
>> >>
>> >> In VM POV, kvm and random memory hogging processes are customers.
>> >> If we handle ballooning specially with disable OOM, what happens other
>> >> processes requires memory at same time? Should they wait for balloon
>> >> driver to release memory?
>> >>
>> >> I don't know your point. Sorry.
>> >> Could you explain your scenario in detail for justify your idea?
>> >
>> > What you said make sense I understand what you said now. Lets ignore
>> > my above argue and see what I'm actually doing.
>> >
>> > I'm hacking with balloon driver to fit to short the vm migration time.
>> >
>> > while migrating host tell guest to balloon as much memory as it can, then start
>> > migrate, just skip the ballooned pages, after migration done tell
>> > guest to release the memory.
>> >
>> > In migration case oom is not I want to see and disable oom will be good.
>>
>> BTW, if oom_killer_disabled is really not recommended to use I can
>> switch back to oom_notifier way.
>
> Could you please explain why you dislike oom_notifier and what problem
> you faced? I haven't understand why oom_notifier is bad. probably my
> less knowledge of balloon is a reason.
>

Both is fine for me indeed, oom_killer_disable is more simple to use
instead. I ever sent a oom_notifier patch last year and did not get
much intention, I can refresh and resend it.

-- 
Regards
dave
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