[PATCH 2/2] powerpc/mm: Ensure "special" zones are empty

Oliver O'Halloran oohall at gmail.com
Thu May 5 16:24:42 AEST 2016

The mm zone mechanism was traditionally used by arch specific code to
partition memory into allocation zones. However there are several zones
that are managed by the mm subsystem rather than the architecture. Most
architectures set the max PFN of these special zones to zero, however on
powerpc we set them to ~0ul. This, in conjunction with a bug in
free_area_init_nodes() results in all of system memory being placed
being placed in ZONE_DEVICE when enabled. Device memory cannot be used
for regular kernel memory allocations so this will cause a kernel panic at

Given the planned addition of more mm managed zones (ZONE_CMA) we should
aim to be consistent with every other architecture and set the max PFN
for these zones to zero

Signed-off-by: Oliver O'Halloran <oohall at gmail.com>
 arch/powerpc/mm/mem.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
index 8f4c19789a38..f0a058ebb6d7 100644
--- a/arch/powerpc/mm/mem.c
+++ b/arch/powerpc/mm/mem.c
@@ -239,8 +239,14 @@ static int __init mark_nonram_nosave(void)
 static bool zone_limits_final;
+ * The memory zones past TOP_ZONE are managed by the generic
+ * mm subsystem which expects the max PFN for these zones
+ * to be set to zero.
+ */
 static unsigned long max_zone_pfns[MAX_NR_ZONES] = {
-	[0 ... MAX_NR_ZONES - 1] = ~0UL
+	[0        ... TOP_ZONE     - 1] = ~0UL,
+	[TOP_ZONE ... MAX_NR_ZONES - 1] = 0

More information about the Linuxppc-dev mailing list