Re: [patch]x86: arch_add_memory round up address

> > On Thu, Oct 09, 2008 at 02:40:34PM +0800, Yinghai Lu wrote: > > > On Wed, Oct 8, 2008 at 11:28 PM, Shaohua Li <shaohua.li@intel.com> wrote: > > > > On Thu, Oct 09, 2008 at 02:22:50PM +0800, Yinghai Lu wrote: > > > >> On Wed, Oct 8, 2008 at 11:08 PM, Shaohua Li <shaohua.li@intel.com> wrote: > > > >> > On Thu, 2008-10-09 at 14:04 +0800, Yinghai Lu wrote: > > > >> >> On Wed, Oct 8, 2008 at 10:31 PM, Shaohua Li <shaohua.li@intel.com> wrote: > > > >> >> > Round up address to a page, otherwise the last page isn't mapped. > > > >> >> > > > > >> >> > Signed-off-by: Shaohua Li <shaohua.li@intel.com> > > > >> >> > --- > > > >> >> > arch/x86/mm/init_64.c | 3 ++- > > > >> >> > 1 file changed, 2 insertions(+), 1 deletion(-) > > > >> >> > > > > >> >> > Index: linux/arch/x86/mm/init_64.c > > > >> >> > =================================================================== > > > >> >> > --- linux.orig/arch/x86/mm/init_64.c 2008-10-09 11:42:33.000000000 +0800 > > > >> >> > +++ linux/arch/x86/mm/init_64.c 2008-10-09 11:43:22.000000000 +0800 > > > >> >> > @@ -721,7 +721,8 @@ int arch_add_memory(int nid, u64 start, > > > >> >> > unsigned long nr_pages = size >> PAGE_SHIFT; > > > >> >> > int ret; > > > >> >> > > > > >> >> > - last_mapped_pfn = init_memory_mapping(start, start + size-1); > > > >> >> > + last_mapped_pfn = init_memory_mapping(start, > > > >> >> > + round_up(start + size-1, PAGE_SIZE)); > > > >> >> > if (last_mapped_pfn > max_pfn_mapped) > > > >> >> > max_pfn_mapped = last_mapped_pfn; > > > >> >> > > > >> >> should use > > > >> >> > > > >> >> last_mapped_pfn = init_memory_mapping(start, start + size); > > > >> > No, this still can't guarantee page aligned, though this works in my > > > >> > test > > > >> > > > >> who will call arch_add_memory? that should be start and size already > > > >> be page aligned. > > > > It's memory hotplug. Doing a round up is always ok and safe even it might be already aligned. > > > > > > > > > > it seems rounding up in that case is wrong... > > > > > > if the caller call that funtion with extra half page, you don't need > > > map that half page, because you can not use it. > > shouldn't we mark such page as reserved and so it will not be used? This is the way we handle hole. > > Just curious, > have you ever seen a real machine which needs this patch?