linux-kernel - Re: 2.6.22 -mm merge plans: slub

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Date:	Wed, 2 May 2007 10:25:47 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Hugh Dickins <hugh@...itas.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>, haveblue@....com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: 2.6.22 -mm merge plans: slub

On Wed, 2 May 2007, Hugh Dickins wrote:

> I presume the answer is just to extend your quicklist work to
> powerpc's lowest level of pagetables.  The only other architecture
> which is using kmem_cache for them is arm26, which has
> "#error SMP is not supported", so won't be giving this problem.

In the meantime we would need something like this to disable SLUB in this 
particular configuration. Note that I have not tested this and the <= for
the comparision with SPLIT_PTLOCK_CPUS may not work (Never seen such a
construct in a Kconfig file but it is needed here).



PowerPC: Disable SLUB for configurations in which slab page structs are modified

PowerPC uses the slab allocator to manage the lowest level of the page table.
In high cpu configurations we also use the page struct to split the page
table lock. Disallow the selection of SLUB for that case.

[Not tested: I am not familiar with powerpc build procedures etc]

Signed-off-by: Christoph Lameter <clameter@....com>

Index: linux-2.6.21-rc7-mm2/arch/powerpc/Kconfig
===================================================================
--- linux-2.6.21-rc7-mm2.orig/arch/powerpc/Kconfig	2007-05-02 10:07:34.000000000 -0700
+++ linux-2.6.21-rc7-mm2/arch/powerpc/Kconfig	2007-05-02 10:13:37.000000000 -0700
@@ -117,6 +117,19 @@ config GENERIC_BUG
 	default y
 	depends on BUG
 
+#
+# Powerpc uses the slab allocator to manage its ptes and the
+# page structs of ptes are used for splitting the page table
+# lock for configurations supporting more than SPLIT_PTLOCK_CPUS.
+#
+# In that special configuration the page structs of slabs are modified.
+# This setting disables the selection of SLUB as a slab allocator.
+#
+config ARCH_USES_SLAB_PAGE_STRUCT
+	bool
+	default y
+	depends on SPLIT_PTLOCK_CPUS <= NR_CPUS
+
 config DEFAULT_UIMAGE
 	bool
 	help
-
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