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

[Dave Young]

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?

>
> Thanks.
>
>
>> Â Â Â for (vb->num_pfns = 0; vb->num_pfns < num; vb->num_pfns++) {
>> Â Â Â Â Â Â Â struct page *page = alloc_page(GFP_HIGHUSER | __GFP_NORETRY |
>> Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â __GFP_NOMEMALLOC | __GFP_NOWARN);
>> @@ -119,6 +121,7 @@ static void fill_balloon(struct virtio_b
>> Â Â Â Â Â Â Â vb->num_pages++;
>> Â Â Â Â Â Â Â list_add(&page->lru, &vb->pages);
>> Â Â Â }
>> + Â Â oom_killer_enable();
>>
>> Â Â Â /* Didn't get any? ÂOh well. */
>> Â Â Â if (vb->num_pfns == 0)
>> --
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>
>
>
>



-- 
Regards
dave
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