linux-kernel - Re: [patch]x86: arch_add

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Date:	Thu, 9 Oct 2008 14:28:31 +0800
From:	Shaohua Li <shaohua.li@...el.com>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...hat.com>
Subject: Re: [patch]x86: arch_add_memory round up address

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@...el.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@...el.com> wrote:
> >> > Round up address to a page, otherwise the last page isn't mapped.
> >> >
> >> > Signed-off-by: Shaohua Li <shaohua.li@...el.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.
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