Subject: page allocator: Use only a single per_cpu_pageset for bootstrapping

We bring up processors one by one. If there is no concurrency then we can
get away with only a single per_cpu_pageset for bootstrap. The bootstrap
pageset will be left in its initial condition once the bootstrap of
a single processor has finished. The existing per cpu pagesets are
already used for multiple zones. They are already used in this fashion.

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

---
 mm/page_alloc.c |   20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

Index: linux-2.6/mm/page_alloc.c
===================================================================
--- linux-2.6.orig/mm/page_alloc.c	2008-04-28 14:42:28.372400669 -0700
+++ linux-2.6/mm/page_alloc.c	2008-04-28 14:55:08.443189768 -0700
@@ -2655,11 +2655,24 @@ static void setup_pagelist_highmark(stru
  * unused processors and/or zones. They do play a role for bootstrapping
  * hotplugged processors.
  *
+ * The use of the pageset assumes that only one processor at a time
+ * will use the pageset for bootstrapping. This means that multiple
+ * processors cannot be simultenaously be bootstrapped. The boot
+ * pageset is configured in such a way that it does not queue pages but
+ * directly call in to the slow patch for both allocate and free.
+ *
  * zoneinfo_show() and maybe other functions do
  * not check if the processor is online before following the pageset pointer.
  * Other parts of the kernel may not check if the zone is available.
  */
-static struct per_cpu_pageset boot_pageset[NR_CPUS];
+static struct per_cpu_pageset boot_pageset = { {
+		.count = 0,
+		.high = 0,
+		.batch = 1,
+		.list = LIST_HEAD_INIT(boot_pageset.pcp.list)
+	},
+	.stat_threshold = 1
+};
 
 /*
  * Dynamically allocate memory for the
@@ -2710,7 +2723,7 @@ static inline void free_zone_pagesets(in
 		struct per_cpu_pageset *pset = zone_pcp(zone, cpu);
 
 		/* Free per_cpu_pageset if it is slab allocated */
-		if (pset != &boot_pageset[cpu])
+		if (pset != &boot_pageset)
 			kfree(pset);
 		zone_pcp(zone, cpu) = NULL;
 	}
@@ -2810,8 +2823,7 @@ static __meminit void zone_pcp_init(stru
 	for (cpu = 0; cpu < NR_CPUS; cpu++) {
 #ifdef CONFIG_NUMA
 		/* Early boot. Slab allocator not functional yet */
-		zone_pcp(zone, cpu) = &boot_pageset[cpu];
-		setup_pageset(&boot_pageset[cpu],0);
+		zone_pcp(zone, cpu) = &boot_pageset;
 #else
 		setup_pageset(zone_pcp(zone,cpu), batch);
 #endif