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

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Date:	Tue, 26 Apr 2011 15:09:06 +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 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?

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



-- 
Regards
dave
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