On ARM max_pfn and max_low_pfn have always been relative to the first valid PFN, apparently due to ancient kernels being unable to properly handle physical memory at addresses other than 0. A comment was added: Note: max_low_pfn and max_pfn reflect the number of _pages_ in the system, not the maximum PFN. which conflicts with the comment in include/linux/bootmem.h that says max_pfn is the highest page. Since then, the number of users of max_pfn has proliferated, and they all seem to assume that max_pfn is the highest valid pfn. The only user of max_low_pfn as a number of pfns instead of the highest pfn is kcore, which conflates max_low_pfn with the size of low memory, but it is not supported on ARM.
Remove the PHYS_PFN_OFFSET subtraction from max_pfn and max_low_pfn, and fix up the rest of ARM mm init that adds it back again. This fixes reading page map counts and flags from /proc/kpagecount and /proc/kpageflags, which will return a short read when reading pfns that overlap with max_pfn, and return 0 when reading pfn max_pfn, making it impossible to read the flags and count for pfn max_pfn. >From code inspection, I believe this will also improve block device performance where the bounce limit was set to BLK_BOUNCE_HIGH, which was bouncing unnecessarily for the top PHYS_PFN_OFFSET pages of low memory. Signed-off-by: Colin Cross <[email protected]> --- arch/arm/mm/init.c | 21 ++++++--------------- 1 file changed, 6 insertions(+), 15 deletions(-) Boot tested on 3.4 and filled up all of memory without any issues. diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c index 9a5cdc0..b4e4051 100644 --- a/arch/arm/mm/init.c +++ b/arch/arm/mm/init.c @@ -415,16 +415,8 @@ void __init bootmem_init(void) */ arm_bootmem_free(min, max_low, max_high); - /* - * This doesn't seem to be used by the Linux memory manager any - * more, but is used by ll_rw_block. If we can get rid of it, we - * also get rid of some of the stuff above as well. - * - * Note: max_low_pfn and max_pfn reflect the number of _pages_ in - * the system, not the maximum PFN. - */ - max_low_pfn = max_low - PHYS_PFN_OFFSET; - max_pfn = max_high - PHYS_PFN_OFFSET; + max_low_pfn = max_low; + max_pfn = max_high; } /* @@ -530,7 +522,6 @@ static inline void free_area_high(unsigned long pfn, unsigned long end) static void __init free_highpages(void) { #ifdef CONFIG_HIGHMEM - unsigned long max_low = max_low_pfn + PHYS_PFN_OFFSET; struct memblock_region *mem, *res; /* set highmem page free */ @@ -539,12 +530,12 @@ static void __init free_highpages(void) unsigned long end = memblock_region_memory_end_pfn(mem); /* Ignore complete lowmem entries */ - if (end <= max_low) + if (end <= max_low_pfn) continue; /* Truncate partial highmem entries */ - if (start < max_low) - start = max_low; + if (start < max_low_pfn) + start = max_low_pfn; /* Find and exclude any reserved regions */ for_each_memblock(reserved, res) { @@ -591,7 +582,7 @@ void __init mem_init(void) extern u32 itcm_end; #endif - max_mapnr = pfn_to_page(max_pfn + PHYS_PFN_OFFSET) - mem_map; + max_mapnr = pfn_to_page(max_pfn) - mem_map; /* this will put all unused low memory onto the freelists */ free_unused_memmap(&meminfo); -- 1.8.3 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
