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Subject: Re: [PATCH 2/2] hv_balloon: do adjust_managed_page_count() when
 ballooning/un-ballooning
To:     Vitaly Kuznetsov <vkuznets@redhat.com>,
        linux-hyperv@vger.kernel.org
Cc:     Wei Liu <wei.liu@kernel.org>,
        Stephen Hemminger <sthemmin@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        Michael Kelley <mikelley@microsoft.com>,
        Dexuan Cui <decui@microsoft.com>, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org
References: <20201202161245.2406143-1-vkuznets@redhat.com>
 <20201202161245.2406143-3-vkuznets@redhat.com>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat GmbH
Message-ID: <9202aafa-f30e-4d96-72a9-3ccd083cc58c@redhat.com>
Date:   Thu, 3 Dec 2020 17:13:15 +0100
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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@redhat.com>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> ---
>  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.

LGTM

Reviewed-by: David Hildenbrand <david@redhat.com>

-- 
Thanks,

David / dhildenb