From e80d6a248298721e0ec2cac150c539d8378577d8 Mon Sep 17 00:00:00 2001 From: Mel Gorman Date: Thu, 14 Aug 2008 11:10:14 +0100 Subject: [ARM] Skip memory holes in FLATMEM when reading /proc/pagetypeinfo Ordinarily, memory holes in flatmem still have a valid memmap and is safe to use. However, an architecture (ARM) frees up the memmap backing memory holes on the assumption it is never used. /proc/pagetypeinfo reads the whole range of pages in a zone believing that the memmap is valid and that pfn_valid will return false if it is not. On ARM, freeing the memmap breaks the page->zone linkages even though pfn_valid() returns true and the kernel can oops shortly afterwards due to accessing a bogus struct zone *. This patch lets architectures say when FLATMEM can have holes in the memmap. Rather than an expensive check for valid memory, /proc/pagetypeinfo will confirm that the page linkages are still valid by checking page->zone is still the expected zone. The lookup of page_zone is safe as there is a limited range of memory that is accessed when calling page_zone. Even if page_zone happens to return the correct zone, the impact is that the counters in /proc/pagetypeinfo are slightly off but fragmentation monitoring is unlikely to be relevant on an embedded system. Reported-by: H Hartley Sweeten Signed-off-by: Mel Gorman Tested-by: H Hartley Sweeten Signed-off-by: Russell King --- arch/arm/Kconfig | 5 +++++ 1 file changed, 5 insertions(+) (limited to 'arch/arm/Kconfig') diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig index 4b8acd2851f4..70dba1668907 100644 --- a/arch/arm/Kconfig +++ b/arch/arm/Kconfig @@ -810,6 +810,11 @@ config OABI_COMPAT UNPREDICTABLE (in fact it can be predicted that it won't work at all). If in doubt say Y. +config ARCH_FLATMEM_HAS_HOLES + bool + default y + depends on FLATMEM + config ARCH_DISCONTIGMEM_ENABLE bool default (ARCH_LH7A40X && !LH7A40X_CONTIGMEM) -- cgit v1.2.1