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authorMel Gorman <mel@csn.ul.ie>2008-08-14 11:10:14 +0100
committerRussell King <rmk+kernel@arm.linux.org.uk>2008-08-27 20:09:28 +0100
commite80d6a248298721e0ec2cac150c539d8378577d8 (patch)
parentf1bcf7e3e734ea8713e08fbc3409f8bf26ec418f (diff)
[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 <hsweeten@visionengravers.com> Signed-off-by: Mel Gorman <mel@csn.ul.ie> Tested-by: H Hartley Sweeten <hsweeten@visionengravers.com> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
2 files changed, 23 insertions, 1 deletions
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.
+ bool
+ default y
+ depends on FLATMEM
default (ARCH_LH7A40X && !LH7A40X_CONTIGMEM)
diff --git a/mm/vmstat.c b/mm/vmstat.c
index b0d08e667ece..d7826af2fb07 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -516,9 +516,26 @@ static void pagetypeinfo_showblockcount_print(struct seq_file *m,
page = pfn_to_page(pfn);
+ /*
+ * Ordinarily, memory holes in flatmem still have a valid
+ * memmap for the PFN range. However, an architecture for
+ * embedded systems (e.g. ARM) can free up the memmap backing
+ * holes to save memory on the assumption the memmap is
+ * never used. The page_zone linkages are then broken even
+ * though pfn_valid() returns true. Skip the page if the
+ * linkages are broken. Even if this test passed, the impact
+ * is that the counters for the movable type are off but
+ * fragmentation monitoring is likely meaningless on small
+ * systems.
+ */
+ if (page_zone(page) != zone)
+ continue;
mtype = get_pageblock_migratetype(page);
- count[mtype]++;
+ if (mtype < MIGRATE_TYPES)
+ count[mtype]++;
/* Print counts */

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