linux-kernel - [PATCH -mmotm] mm: init_per_zone_pages_min - get rid of sqrt call on small machines

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Message-ID: <20090506061953.GA16057@lenovo>
Date:	Wed, 6 May 2009 10:19:53 +0400
From:	Cyrill Gorcunov <gorcunov@...nvz.org>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	David Rientjes <rientjes@...gle.com>
Cc:	LMMML <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH -mmotm] mm: init_per_zone_pages_min - get rid of sqrt call
	on small machines

For small machines we may eliminate call for int_sqrt
by using precaulculated value.

CC: David Rientjes <rientjes@...gle.com>
Signed-off-by: Cyrill Gorcunov <gorcunov@...nvz.org>
---
 mm/page_alloc.c |   12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

Index: linux-2.6.git/mm/page_alloc.c
=====================================================================
--- linux-2.6.git.orig/mm/page_alloc.c
+++ linux-2.6.git/mm/page_alloc.c
@@ -4610,11 +4610,15 @@ static int __init init_per_zone_pages_mi
 
 	lowmem_kbytes = nr_free_buffer_pages() * (PAGE_SIZE >> 10);
 
-	min_free_kbytes = int_sqrt(lowmem_kbytes * 16);
-	if (min_free_kbytes < 128)
+	/* for small values we may eliminate sqrt operation completely */
+	if (lowmem_kbytes < 1024)
 		min_free_kbytes = 128;
-	if (min_free_kbytes > 65536)
-		min_free_kbytes = 65536;
+	else {
+		min_free_kbytes = int_sqrt(lowmem_kbytes * 16);
+		if (min_free_kbytes > 65536)
+			min_free_kbytes = 65536;
+	}
+
 	setup_per_zone_pages_min();
 	setup_per_zone_lowmem_reserve();
 	setup_per_zone_inactive_ratio();

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