linux-kernel - Re: [PATCH] Drivers: hv: hv_balloon: eliminate jumps in piecewiese linear floor function

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Date:	Thu, 26 Mar 2015 17:17:46 +0100
From:	Laszlo Ersek <lersek@...hat.com>
To:	Vitaly Kuznetsov <vkuznets@...hat.com>,
	"K. Y. Srinivasan" <kys@...rosoft.com>
CC:	Haiyang Zhang <haiyangz@...rosoft.com>,
	devel@...uxdriverproject.org, linux-kernel@...r.kernel.org,
	Dexuan Cui <decui@...rosoft.com>
Subject: Re: [PATCH] Drivers: hv: hv_balloon: eliminate jumps in piecewiese
 linear floor function

On 03/26/15 11:26, Vitaly Kuznetsov wrote:
> Commit 79208c57da53 ("Drivers: hv: hv_balloon: Make adjustments in computing
> the floor") was inacurate as it introduced a jump in our piecewiese linear
> 'floor' function:
> 
> At 2048MB we have:
> Left limit:
> 104 + 2048/8 = 360
> Right limit:
> 256 + 2048/16 = 384 (so the right value is 232)
> 
> We now have to make an adjustment at 8192 boundary:
> 232 + 8192/16 = 744
> 512 + 8192/32 = 768 (so the right value is 488)
> 
> Suggested-by: Laszlo Ersek <lersek@...hat.com>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> ---
>  drivers/hv/hv_balloon.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c
> index 014256a..16d52da 100644
> --- a/drivers/hv/hv_balloon.c
> +++ b/drivers/hv/hv_balloon.c
> @@ -966,8 +966,8 @@ static unsigned long compute_balloon_floor(void)
>  	 *     128        72    (1/2)
>  	 *     512       168    (1/4)
>  	 *    2048       360    (1/8)
> -	 *    8192       768    (1/16)
> -	 *   32768      1536	(1/32)
> +	 *    8192       744    (1/16)
> +	 *   32768      1512	(1/32)
>  	 */
>  	if (totalram_pages < MB2PAGES(128))
>  		min_pages = MB2PAGES(8) + (totalram_pages >> 1);
> @@ -976,9 +976,9 @@ static unsigned long compute_balloon_floor(void)
>  	else if (totalram_pages < MB2PAGES(2048))
>  		min_pages = MB2PAGES(104) + (totalram_pages >> 3);
>  	else if (totalram_pages < MB2PAGES(8192))
> -		min_pages = MB2PAGES(256) + (totalram_pages >> 4);
> +		min_pages = MB2PAGES(232) + (totalram_pages >> 4);
>  	else
> -		min_pages = MB2PAGES(512) + (totalram_pages >> 5);
> +		min_pages = MB2PAGES(488) + (totalram_pages >> 5);
>  #undef MB2PAGES
>  	return min_pages;
>  }
> 

Reviewed-by: Laszlo Ersek <lersek@...hat.com>

Thanks!
Laszlo
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