linux-kernel - [rfc][patch 1/3] slub: fix small HWCACHE

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Date:	Mon, 3 Mar 2008 10:34:49 +0100
From:	Nick Piggin <npiggin@...e.de>
To:	netdev@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	yanmin_zhang@...ux.intel.com, David Miller <davem@...emloft.net>,
	Christoph Lameter <clameter@...r.sgi.com>,
	Eric Dumazet <dada1@...mosbay.com>
Subject: [rfc][patch 1/3] slub: fix small HWCACHE_ALIGN alignment


SLUB should pack even small objects nicely into cachelines if that is what
has been asked for. Use the same algorithm as SLAB for this.

Signed-off-by: Nick Piggin <npiggin@...e.de>
---
Index: linux-2.6/mm/slub.c
===================================================================
--- linux-2.6.orig/mm/slub.c
+++ linux-2.6/mm/slub.c
@@ -1896,12 +1896,15 @@ static unsigned long calculate_alignment
 	 * specified alignment though. If that is greater
 	 * then use it.
 	 */
-	if ((flags & SLAB_HWCACHE_ALIGN) &&
-			size > cache_line_size() / 2)
-		return max_t(unsigned long, align, cache_line_size());
+	if (flags & SLAB_HWCACHE_ALIGN) {
+		unsigned long ralign = cache_line_size();
+		while (size <= ralign / 2)
+			ralign /= 2;
+		align = max(align, ralign);
+	}
 
 	if (align < ARCH_SLAB_MINALIGN)
-		return ARCH_SLAB_MINALIGN;
+		align = ARCH_SLAB_MINALIGN;
 
 	return ALIGN(align, sizeof(void *));
 }
--
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