linux-kernel - Re: [PATCH 1/2] virtio_balloon: disable oom killer when fill balloon

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Message-ID: <BANLkTinosxKZ9WnAHsfbaOgNx2q1+CxFRw@mail.gmail.com>
Date:	Tue, 26 Apr 2011 16:47:19 +0800
From:	Dave Young <hidave.darkstar@...il.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] virtio_balloon: disable oom killer when fill balloon

On Tue, Apr 26, 2011 at 3:22 PM, KOSAKI Motohiro
<kosaki.motohiro@...fujitsu.com> wrote:
>> On Tue, Apr 26, 2011 at 2:38 PM, KOSAKI Motohiro
>> <kosaki.motohiro@...fujitsu.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.
>> >>
>> >> Here disable oom killer in fill_balloon to address this issue.
>> >>
>> >> Signed-off-by: Dave Young <hidave.darkstar@...il.com>
>> >> ---
>> >>  drivers/virtio/virtio_balloon.c |    3 +++
>> >>  1 file changed, 3 insertions(+)
>> >>
>> >> --- linux-2.6.orig/drivers/virtio/virtio_balloon.c    2010-10-13 10:14:38.000000000 +0800
>> >> +++ linux-2.6/drivers/virtio/virtio_balloon.c 2011-04-26 11:38:43.979785141 +0800
>> >> @@ -25,6 +25,7 @@
>> >>  #include <linux/freezer.h>
>> >>  #include <linux/delay.h>
>> >>  #include <linux/slab.h>
>> >> +#include <linux/oom.h>
>> >>
>> >>  struct virtio_balloon
>> >>  {
>> >> @@ -102,6 +103,7 @@ static void fill_balloon(struct virtio_b
>> >>       /* We can only do one array worth at a time. */
>> >>       num = min(num, ARRAY_SIZE(vb->pfns));
>> >>
>> >> +     oom_killer_disable();
>> >
>> > I think this patch need proper comment at least. My first impression
>> > is, "Hm, __GFP_NORETRY should prevent oom, why is this necessary?".
>> > So, this actually prevent _another_ thread call out_of_memory().
>>
>> Thanks, will fix.
>>
>> > Also, Here doesn't have any exclusion against hibernation (ie another
>> > oom_killer_disable() callsite). It should be described why lock is
>> > unnecessary.
>>
>> Good catch, but lock should better be handled in oom_killer_disable
>> function itself,
>> What do you think?
>>
>> For oom killer multi user there's more problem, if process A disable
>> oom killer then Process B enable oom killer, it is not A want to see,
>> Any thoughts?
>
> If baloon and hibernation don't have any implicit exclusion, you are
> right.

For this case, hibernation will freeze balloon thread before call
oom_killer_disable, so there's no problem.

If we consider future users of oom_killer_disabled, we will
have to deal with it.

>
> Sorry, I don't virtio internal. please don't ask me.
>
>
>
>



-- 
Regards
dave
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