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Date: Mon, 16 Jun 2008 22:26:29 +0900
From: Yasunori Goto <y-goto@jp.fujitsu.com>
To: Andy Whitcroft <apw@shadowen.org>
Subject: Re: [Patch 002/005](memory hotplug) align memmap to page size
Cc: Badari Pulavarty <pbadari@us.ibm.com>,
       Andrew Morton <akpm@linux-foundation.org>,
       Linux Kernel ML <linux-kernel@vger.kernel.org>,
       linux-mm <linux-mm@kvack.org>, Yinghai Lu <yhlu.kernel@gmail.com>
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> On Mon, Apr 07, 2008 at 09:46:19PM +0900, Yasunori Goto wrote:
> > To free memmap easier, this patch aligns it to page size.
> > Bootmem allocater may mix some objects in one pages.
> > It's not good for freeing memmap of memory hot-remove.
> > 
> > 
> > Signed-off-by: Yasunori Goto <y-goto@jp.fujitsu.com>
> > 
> > ---
> >  mm/sparse.c |    4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > Index: current/mm/sparse.c
> > ===================================================================
> > --- current.orig/mm/sparse.c	2008-04-07 19:18:50.000000000 +0900
> > +++ current/mm/sparse.c	2008-04-07 20:08:13.000000000 +0900
> > @@ -265,8 +265,8 @@
> >  	if (map)
> >  		return map;
> >  
> > -	map = alloc_bootmem_node(NODE_DATA(nid),
> > -			sizeof(struct page) * PAGES_PER_SECTION);
> > +	map = alloc_bootmem_pages_node(NODE_DATA(nid),
> > +		       PAGE_ALIGN(sizeof(struct page) * PAGES_PER_SECTION));
> >  	return map;
> >  }
> >  #endif /* !CONFIG_SPARSEMEM_VMEMMAP */
> 
> Ahh ok, we do makes sure the mmap uses up the rest of the space.  That
> though is a shame as we cannot slip the usemap in the end of the space
> any more (assuming we could).

I thought we could merge memmap and usemap page in same pages. However,
if memmap' size equals page size correctly, one page must be used for
only one usemap in the end. 

Bye.

-- 
Yasunori Goto