diff options
| author | Mel Gorman <mel@csn.ul.ie> | 2008-08-14 11:10:14 +0100 |
|---|---|---|
| committer | Russell King <rmk+kernel@arm.linux.org.uk> | 2008-08-27 20:09:28 +0100 |
| commit | e80d6a248298721e0ec2cac150c539d8378577d8 (patch) | |
| tree | 0ad2112037cc28e3faab41baf2b6ea1851748019 | |
| parent | f1bcf7e3e734ea8713e08fbc3409f8bf26ec418f (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>
| -rw-r--r-- | arch/arm/Kconfig | 5 | ||||
| -rw-r--r-- | mm/vmstat.c | 19 |
2 files changed, 23 insertions, 1 deletions
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig index 4b8acd2851f..70dba166890 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 b0d08e667ec..d7826af2fb0 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 */ |