On Tue, Sep 28, 2010 at 9:49 PM, Dave Young <[email protected]> wrote:
> On Tue, Sep 28, 2010 at 9:34 PM, Anthony Liguori <[email protected]>
> wrote:
>> On 09/28/2010 08:19 AM, Dave Young wrote:
>>>
>>> Balloon could cause guest memory oom killing and panic. If we disable the
>>> oom killer it will be better at least avoid guest panic.
>>>
>>> If alloc failed we can just adjust the balloon target to be equal to
>>> current number by call vdev->config->set
>>>
>>> But during test I found the config->set num_pages does not change the
>>> config actually, Should I do hacks in userspace as well? If so where should
>>> I start to hack?
>>>
>>
>
> Hi,
>
> Thanks your comments.
>
>> The guest is not supposed to set the target field in it's config. This is a
>> host read/write, guest read-only field.
>
> Could you tell where to set it? If so, IMHO set config api should
> fail, isn't it?
Get it, in hw/virtio-balloon.c function virtio_balloon_set_config
>
>>
>> The problem with your approach generally speaking is that it's unclear
>> whether this is the right policy. For instance, what if another application
>> held a very large allocation which caused the fill request to stop but then
>> shortly afterwards, the aforementioned application released that allocation.
>> If instead of just stopping, we paused and tried again later, we could
>> potentially succeed.
>
> Yes, it is possible. But maybe better to do balloon from qemu monitor later?
>
>>
>> I think a better approach might be a graceful back off. For instance, when
>> you hit this condition, deflate the balloon by 10% based on the assumption
>> that you probably already gone too far. Before you attempt to allocate to
>> the target again, set a timeout that increases in duration exponentially
>> until you reach some maximum (say 10s).
>
> I'm afraid most times it will keep doing inflate/deflate circularly.
>
>>
>> This isn't the only approach, but hopefully it conveys the idea of
>> gracefully backing off without really giving up.
>>
>> Regards,
>>
>> Anthony Liguori
>>
>>> Thanks
>>>
>>> --- linux-2.6.orig/drivers/virtio/virtio_balloon.c 2010-09-25
>>> 20:58:14.190000001 +0800
>>> +++ linux-2.6/drivers/virtio/virtio_balloon.c 2010-09-28
>>> 21:05:42.203333675 +0800
>>> @@ -25,6 +25,7 @@
>>> #include<linux/freezer.h>
>>> #include<linux/delay.h>
>>> #include<linux/slab.h>
>>> +#include<linux/oom.h>
>>>
>>> struct virtio_balloon
>>> {
>>> @@ -97,8 +98,22 @@ static void tell_host(struct virtio_ball
>>> wait_for_completion(&vb->acked);
>>> }
>>>
>>> -static void fill_balloon(struct virtio_balloon *vb, size_t num)
>>> +static int cblimit(int times)
>>> {
>>> + static int t;
>>> +
>>> + if (t< times)
>>> + t++;
>>> + else
>>> + t = 0;
>>> +
>>> + return !t;
>>> +}
>>> +
>>> +static int fill_balloon(struct virtio_balloon *vb, size_t num)
>>> +{
>>> + int ret = 0;
>>> +
>>> /* We can only do one array worth at a time. */
>>> num = min(num, ARRAY_SIZE(vb->pfns));
>>>
>>> @@ -106,10 +121,13 @@ static void fill_balloon(struct virtio_b
>>> struct page *page = alloc_page(GFP_HIGHUSER | __GFP_NORETRY
>>> |
>>> __GFP_NOMEMALLOC | __GFP_NOWARN);
>>> if (!page) {
>>> - if (printk_ratelimit())
>>> + if (cblimit(5)) {
>>> dev_printk(KERN_INFO,&vb->vdev->dev,
>>> "Out of puff! Can't get %zu
>>> pages\n",
>>> num);
>>> + ret = -ENOMEM;
>>> + goto out;
>>> + }
>>> /* Sleep for at least 1/5 of a second before retry.
>>> */
>>> msleep(200);
>>> break;
>>> @@ -120,11 +138,11 @@ static void fill_balloon(struct virtio_b
>>> list_add(&page->lru,&vb->pages);
>>> }
>>>
>>> - /* Didn't get any? Oh well. */
>>> - if (vb->num_pfns == 0)
>>> - return;
>>> +out:
>>> + if (vb->num_pfns)
>>> + tell_host(vb, vb->inflate_vq);
>>>
>>> - tell_host(vb, vb->inflate_vq);
>>> + return ret;
>>> }
>>>
>>> static void release_pages_by_pfn(const u32 pfns[], unsigned int num)
>>> @@ -251,6 +269,14 @@ static void update_balloon_size(struct v
>>> &actual, sizeof(actual));
>>> }
>>>
>>> +static void update_balloon_target(struct virtio_balloon *vb)
>>> +{
>>> + __le32 num_pages = cpu_to_le32(vb->num_pages);
>>> + vb->vdev->config->set(vb->vdev,
>>> + offsetof(struct virtio_balloon_config,
>>> num_pages),
>>> + &num_pages, sizeof(num_pages));
>>> +}
>>> +
>>> static int balloon(void *_vballoon)
>>> {
>>> struct virtio_balloon *vb = _vballoon;
>>> @@ -267,9 +293,14 @@ static int balloon(void *_vballoon)
>>> || freezing(current));
>>> if (vb->need_stats_update)
>>> stats_handle_request(vb);
>>> - if (diff> 0)
>>> - fill_balloon(vb, diff);
>>> - else if (diff< 0)
>>> + if (diff> 0) {
>>> + int oom;
>>> + oom_killer_disable();
>>> + oom = fill_balloon(vb, diff);
>>> + oom_killer_enable();
>>> + if (oom)
>>> + update_balloon_target(vb);
>>> + } else if (diff< 0)
>>> leak_balloon(vb, -diff);
>>> update_balloon_size(vb);
>>> }
>>> --
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>>>
>>
>>
>
>
>
> --
> Regards
> dave
>
--
Regards
dave
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