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Date: Fri, 22 Jan 2010 00:17:14 +0100
From: Andrea Arcangeli <aarcange@redhat.com>
Subject: Re: [PATCH 22 of 30] pmd_trans_huge migrate bugcheck
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To: Christoph Lameter <cl@linux-foundation.org>
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On Fri, Jan 22, 2010 at 12:01:27AM +0100, Andrea Arcangeli wrote:
> @@ -833,6 +834,9 @@ static int do_move_page_to_node_array(st
>  				!migrate_all)
>  			goto put_and_set;
>  
> +		if (unlikely(PageTransHuge(page)))
> +			if (unlikely(split_huge_page(page)))
> +				goto put_and_set;
>  		err = isolate_lru_page(page);
>  		if (!err) {
>  			list_add_tail(&page->lru, &pagelist);

This was too fast of a patch, I've to move this a few lines above so
the mapcount check will work too (also note, pagetranshuge bugs on
tail pages and I like to keep it that way to be more strict on the
other users, so it should be replaced by pagecompound in addition to
moving it a little up). refcounting will adjust automatically and
atomically during the split, simply mapcount will be >0 after the split
on the tailpage and the tail_page->_count will be boosted by the mapcount too.

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