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

[KOSAKI Motohiro]

> On Wed, Apr 27, 2011 at 9:37 AM, Dave Young <hidave.darkstar@xxxxxxxxx> wrote:
> > On Wed, Apr 27, 2011 at 7:33 AM, Minchan Kim <minchan.kim@xxxxxxxxx> wrote:
> >> On Tue, Apr 26, 2011 at 6:39 PM, Dave Young <hidave.darkstar@xxxxxxxxx> wrote:
> >>> On Tue, Apr 26, 2011 at 5:28 PM, Minchan Kim <minchan.kim@xxxxxxxxx> wrote:
> >>>> Please resend this with [2/2] to linux-mm.
> >>>>
> >>>> On Tue, Apr 26, 2011 at 5:59 PM, Dave Young <hidave.darkstar@xxxxxxxxx> 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.



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