From: Mel Gorman Date: Thu, 14 Aug 2008 10:10:14 +0000 (+0100) Subject: [ARM] Skip memory holes in FLATMEM when reading /proc/pagetypeinfo X-Git-Tag: v2.6.27-rc5~1^2~2 X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=e80d6a248298721e0ec2cac150c539d8378577d8;p=linux-2.6 [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 --- diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig index 4b8acd2851..70dba16689 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) diff --git a/mm/vmstat.c b/mm/vmstat.c index b0d08e667e..d7826af2fb 100644 --- a/mm/vmstat.c +++ b/mm/vmstat.c @@ -516,9 +516,26 @@ static void pagetypeinfo_showblockcount_print(struct seq_file *m, continue; page = pfn_to_page(pfn); +#ifdef CONFIG_ARCH_FLATMEM_HAS_HOLES + /* + * 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; +#endif mtype = get_pageblock_migratetype(page); - count[mtype]++; + if (mtype < MIGRATE_TYPES) + count[mtype]++; } /* Print counts */