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

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Message-ID: <BANLkTikfyi2FBykk1D1H-tdrSjmRYEh6ug@mail.gmail.com>
Date:	Wed, 27 Apr 2011 09:48:48 +0800
From:	Dave Young <hidave.darkstar@...il.com>
To:	Minchan Kim <minchan.kim@...il.com>
Cc:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	kosaki.motohiro@...fujitsu.com, linux-mm <linux-mm@...ck.org>
Subject: Re: [PATCH v2] virtio_balloon: disable oom killer when fill balloon

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.

>
>> And as I previous said, we have to solve oom_killer_disabled issue in
>> do_try_to_free_pages.
>>
>> Thanks, Dave.
>> --
>> Kind regards,
>> Minchan Kim
>>
>
>
>
> --
> Regards
> dave
>



-- 
Regards
dave
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