David Hildenbrand <david@xxxxxxxxxx> writes:
> On 02.12.20 17:12, Vitaly Kuznetsov wrote:
>> Unlike virtio_balloon/virtio_mem/xen balloon drivers, Hyper-V balloon driver
>> does not adjust managed pages count when ballooning/un-ballooning and this leads
>> to incorrect stats being reported, e.g. unexpected 'free' output.
>>
>> Note, the calculation in post_status() seems to remain correct: ballooned out
>> pages are never 'available' and we manually add dm->num_pages_ballooned to
>> 'commited'.
>>
>> Suggested-by: David Hildenbrand <david@xxxxxxxxxx>
>> Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
>> ---
>> drivers/hv/hv_balloon.c | 5 ++++-
>> 1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c
>> index da3b6bd2367c..8c471823a5af 100644
>> --- a/drivers/hv/hv_balloon.c
>> +++ b/drivers/hv/hv_balloon.c
>> @@ -1198,6 +1198,7 @@ static void free_balloon_pages(struct hv_dynmem_device *dm,
>> __ClearPageOffline(pg);
>> __free_page(pg);
>> dm->num_pages_ballooned--;
>> + adjust_managed_page_count(pg, 1);
>> }
>> }
>>
>> @@ -1238,8 +1239,10 @@ static unsigned int alloc_balloon_pages(struct hv_dynmem_device *dm,
>> split_page(pg, get_order(alloc_unit << PAGE_SHIFT));
>>
>> /* mark all pages offline */
>> - for (j = 0; j < alloc_unit; j++)
>> + for (j = 0; j < alloc_unit; j++) {
>> __SetPageOffline(pg + j);
>> + adjust_managed_page_count(pg + j, -1);
>> + }
>>
>> bl_resp->range_count++;
>> bl_resp->range_array[i].finfo.start_page =
>>
>
> I assume this has been properly tested such that it does not change the
> system behavior regarding when/how HyperV decides to add/remove memory.
>
I'm always reluctant to confirm 'proper testing' as no matter how small
and 'obvious' the change is, regressions keep happening :-) But yes,
this was tested on a Hyper-V host and 'stress' and I observed 'free'
when the balloon was both inflated and deflated, values looked sane.
> LGTM
>
> Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>
Thanks!
--
Vitaly
