On Mon, Mar 18, 2013 at 10:47:41PM -0700, Yinghai Lu wrote: > On Mon, Mar 18, 2013 at 10:15 PM, Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> wrote: > > max_low_pfn reflect the number of _pages_ in the system, > > not the maximum PFN. You can easily find that fact in init_bootmem(). > > So fix it. > > I'm confused. for x86, we have max_low_pfn defined in ... Below is queote from Russell King in 'https://lkml.org/lkml/2013/3/13/123' Now, max_low_pfn is initialized this way: /** * init_bootmem - register boot memory * @start: pfn where the bitmap is to be placed * @pages: number of available physical pages * * Returns the number of bytes needed to hold the bitmap. */ unsigned long __init init_bootmem(unsigned long start, unsigned long pages) { max_low_pfn = pages; min_low_pfn = start; return init_bootmem_core(NODE_DATA(0)->bdata, start, 0, pages); } So, min_low_pfn is the PFN offset of the start of physical memory (so 3GB >> PAGE_SHIFT) and max_low_pfn ends up being the number of pages, _not_ the maximum PFN value So, if physical address doesn't start at 0, max_low_pfn doesn't represent the maximum PFN value. This is a case for ARM. > > #ifdef CONFIG_X86_32 > /* max_low_pfn get updated here */ > find_low_pfn_range(); > #else > num_physpages = max_pfn; > > check_x2apic(); > > /* How many end-of-memory variables you have, grandma! */ > /* need this before calling reserve_initrd */ > if (max_pfn > (1UL<<(32 - PAGE_SHIFT))) > max_low_pfn = e820_end_of_low_ram_pfn(); > else > max_low_pfn = max_pfn; > > and under max_low_pfn is bootmem. > > > > > Additionally, if 'start_pfn == end_pfn', we don't need to go futher, > > so change range check. > > > > Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> > > > > diff --git a/mm/nobootmem.c b/mm/nobootmem.c > > index 5e07d36..4711e91 100644 > > --- a/mm/nobootmem.c > > +++ b/mm/nobootmem.c > > @@ -110,9 +110,9 @@ static unsigned long __init __free_memory_core(phys_addr_t start, > > { > > unsigned long start_pfn = PFN_UP(start); > > unsigned long end_pfn = min_t(unsigned long, > > - PFN_DOWN(end), max_low_pfn); > > + PFN_DOWN(end), min_low_pfn); > > what is min_low_pfn ? is it 0 for x86? My implementation is totally wrong. :) min_low_pfn is not proper value for this purpose. I will fix it. Sorry for noise. Thanks. > > Thanks > > Yinghai > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@xxxxxxxxx. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a> -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>