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Subject[patch 1/7] Increase default reserve percpu area
SLUB now requires a portion of the per cpu reserve. There are on average
about 70 real slabs on a system (aliases do not count) and each needs 12 bytes
of per cpu space. Thats 840 bytes. In debug mode all slabs will be real slabs
which will make us end up with 150 -> 1800.

Things work fine without this patch but then slub will reduce the percpu reserve
for modules.

Percpu data must be available regardless if modules are in use or not. So get
rid of the #ifdef CONFIG_MODULES.

Make the size of the percpu area dependant on the size of a machine word. That
way we have larger sizes for 64 bit machines. 64 bit machines need more percpu
memory since the pointer and counters may have double the size. Plus there is
lots of memory available on 64 bit.

Signed-off-by: Christoph Lameter <>

Index: linux-2.6/include/linux/percpu.h
--- linux-2.6.orig/include/linux/percpu.h 2008-11-05 12:05:46.000000000 -0600
+++ linux-2.6/include/linux/percpu.h 2008-11-05 14:29:15.000000000 -0600
@@ -44,7 +44,7 @@
extern unsigned int percpu_reserve;
/* Enough to cover all DEFINE_PER_CPUs in kernel, including modules. */
+#define PERCPU_RESERVE_SIZE (sizeof(unsigned long) * 2500)

(__per_cpu_end - __per_cpu_start + percpu_reserve)

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