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

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Date:	Thu, 26 Mar 2015 11:26:53 +0100
From:	Vitaly Kuznetsov <vkuznets@...hat.com>
To:	"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>,
	Laszlo Ersek <lersek@...hat.com>
Subject: [PATCH] Drivers: hv: hv_balloon: eliminate jumps in piecewiese linear floor function

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;
 }
-- 
1.9.3

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