powerpc: Dynamically allocate pacas

On 64-bit kernels we currently have a 512 byte struct paca_struct for
each cpu (usually just called "the paca"). Currently they are statically
allocated, which means a kernel built for a large number of cpus will
waste a lot of space if it's booted on a machine with few cpus.

We can avoid that by only allocating the number of pacas we need at
boot. However this is complicated by the fact that we need to access
the paca before we know how many cpus there are in the system.

The solution is to dynamically allocate enough space for NR_CPUS pacas,
but then later in boot when we know how many cpus we have, we free any
unused pacas.

Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 3 insertions, 0 deletions

diff --git a/arch/powerpc/kernel/prom.c b/arch/powerpc/kernel/prom.c
index 43238b2054b6..05131d634e73 100644
--- a/arch/powerpc/kernel/prom.c
+++ b/arch/powerpc/kernel/prom.c
@@ -43,6 +43,7 @@
 #include <asm/smp.h>
 #include <asm/system.h>
 #include <asm/mmu.h>
+#include <asm/paca.h>
 #include <asm/pgtable.h>
 #include <asm/pci.h>
 #include <asm/iommu.h>
@@ -721,6 +722,8 @@ void __init early_init_devtree(void *params)
          * FIXME .. and the initrd too? */
         move_device_tree();
 
+        allocate_pacas();
+
         DBG("Scanning CPUs ...\n");
 
         /* Retreive CPU related informations from the flat tree