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

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Date:	Tue, 26 Apr 2011 17:39:47 +0800
From:	Dave Young <hidave.darkstar@...il.com>
To:	Minchan Kim <minchan.kim@...il.com>
Cc:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	kosaki.motohiro@...fujitsu.com, linux-mm <linux-mm@...ck.org>
Subject: Re: [PATCH v2] virtio_balloon: disable oom killer when fill balloon

On Tue, Apr 26, 2011 at 5:28 PM, Minchan Kim <minchan.kim@...il.com> wrote:
> Please resend this with [2/2] to linux-mm.
>
> On Tue, Apr 26, 2011 at 5:59 PM, Dave Young <hidave.darkstar@...il.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.
>
> 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.

>
>>
>> Here disable oom killer in fill_balloon to address this issue.
>> Add code comment as KOSAKI Motohiro's suggestion.
>>
>> Signed-off-by: Dave Young <hidave.darkstar@...il.com>
>> ---
>>  drivers/virtio/virtio_balloon.c |    8 ++++++++
>>  1 file changed, 8 insertions(+)
>>
>> --- linux-2.6.orig/drivers/virtio/virtio_balloon.c      2011-04-26 11:39:14.053118406 +0800
>> +++ linux-2.6/drivers/virtio/virtio_balloon.c   2011-04-26 16:54:56.419741542 +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 +103,12 @@ static void fill_balloon(struct virtio_b
>>        /* We can only do one array worth at a time. */
>>        num = min(num, ARRAY_SIZE(vb->pfns));
>>
>> +       /* Disable oom killer for indirect oom due to our memory consuming
>> +        * Currently only hibernation code use oom_killer_disable,
>
> Hmm, Please look at current mmotm. Now oom_killer_disabled is used by
> do_try_to_free_pages in mmotm so it could make unnecessary oom kill.
>
> BTW, I can't understand why we need to handle virtio by special.
> Could you explain it in detail? :)
>
>
>
> --
> Kind regards,
> Minchan Kim
>



-- 
Regards
dave
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