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

[Dave Young]

On Tue, Apr 26, 2011 at 3:22 PM, KOSAKI Motohiro
<kosaki.motohiro@xxxxxxxxxxxxxx> wrote:
>> On Tue, Apr 26, 2011 at 2:38 PM, KOSAKI Motohiro
>> <kosaki.motohiro@xxxxxxxxxxxxxx> 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@xxxxxxxxx>
>> >> ---
>> >> Âdrivers/virtio/virtio_balloon.c | Â Â3 +++
>> >> Â1 file changed, 3 insertions(+)
>> >>
>> >> --- linux-2.6.orig/drivers/virtio/virtio_balloon.c  Â2010-10-13 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 @@
>> >> Â#include <linux/freezer.h>
>> >> Â#include <linux/delay.h>
>> >> Â#include <linux/slab.h>
>> >> +#include <linux/oom.h>
>> >>
>> >> Âstruct virtio_balloon
>> >> Â{
>> >> @@ -102,6 +103,7 @@ static void fill_balloon(struct virtio_b
>> >> Â Â Â /* We can only do one array worth at a time. */
>> >> Â Â Â num = min(num, ARRAY_SIZE(vb->pfns));
>> >>
>> >> + Â Â 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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