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Subject: Re: [PATCH 1/2] hv_balloon: simplify math in alloc_balloon_pages()
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>
 <20201202161245.2406143-2-vkuznets@redhat.com>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat GmbH
Message-ID: <47b49c1a-6ea9-9b86-e08c-bb6915d79ea2@redhat.com>
Date:   Thu, 3 Dec 2020 17:15:04 +0100
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On 02.12.20 17:12, Vitaly Kuznetsov wrote:
> 'alloc_unit' in alloc_balloon_pages() is either '512' for 2M allocations or
> '1' for 4k allocations. So
> 
> 1 << get_order(alloc_unit << PAGE_SHIFT)
> 
> equals to 'alloc_unit' and the for loop basically sets all them offline.
> Simplify the math to improve the readability.
> 
> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> ---
>  drivers/hv/hv_balloon.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c
> index eb56e09ae15f..da3b6bd2367c 100644
> --- a/drivers/hv/hv_balloon.c
> +++ b/drivers/hv/hv_balloon.c
> @@ -1238,7 +1238,7 @@ 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 < (1 << get_order(alloc_unit << PAGE_SHIFT)); j++)
> +		for (j = 0; j < alloc_unit; j++)
>  			__SetPageOffline(pg + j);
>  
>  		bl_resp->range_count++;
> 

Right, alloc_unit is multiples of 4k pages, such that it can directly be
used for page ranges in deflation/inflation paths.

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

-- 
Thanks,

David / dhildenb