From 95eaaca93d326d7fefa5288502d52f1a77d55889 Mon Sep 17 00:00:00 2001
From: Nick Piggin <nickpiggin@yahoo.com.au>
Date: Sun, 4 Dec 2005 13:55:25 +1100
Subject: [PATCH] --- yaml --- r: 14967 b: refs/heads/master c:
 0ceaacc9785fedc500e19b024d606a82a23f5372 h: refs/heads/master i:   14965:
 666a538fd1136101de069d263e362398b4cb7e20   14963:
 61cb232601bb0a1c67767a1d4045c932ee8035e1   14959:
 012496fee8179c1af3c8e97b1bc995a1feaebefb v: v3

---
 [refs]                |  2 +-
 trunk/mm/page_alloc.c | 16 ++++++++--------
 2 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/[refs] b/[refs]
index 9ded32873f83..8ac257c0478b 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 9a40525788a1b692ee0fc780a8cdb2ac808de1b0
+refs/heads/master: 0ceaacc9785fedc500e19b024d606a82a23f5372
diff --git a/trunk/mm/page_alloc.c b/trunk/mm/page_alloc.c
index b257720edfc8..3b21a13d841c 100644
--- a/trunk/mm/page_alloc.c
+++ b/trunk/mm/page_alloc.c
@@ -1772,16 +1772,16 @@ static int __devinit zone_batchsize(struct zone *zone)
 		batch = 1;
 
 	/*
-	 * We will be trying to allcoate bigger chunks of contiguous
-	 * memory of the order of fls(batch).  This should result in
-	 * better cache coloring.
+	 * Clamp the batch to a 2^n - 1 value. Having a power
+	 * of 2 value was found to be more likely to have
+	 * suboptimal cache aliasing properties in some cases.
 	 *
-	 * A sanity check also to ensure that batch is still in limits.
+	 * For example if 2 tasks are alternately allocating
+	 * batches of pages, one task can end up with a lot
+	 * of pages of one half of the possible page colors
+	 * and the other with pages of the other colors.
 	 */
-	batch = (1 << fls(batch + batch/2));
-
-	if (fls(batch) >= (PAGE_SHIFT + MAX_ORDER - 2))
-		batch = PAGE_SHIFT + ((MAX_ORDER - 1 - PAGE_SHIFT)/2);
+	batch = (1 << (fls(batch + batch/2)-1)) - 1;
 
 	return batch;
 }