linux-kernel - Re: [PATCH] hugetlb: call mmu notifiers on hugepage cow

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Message-ID: <20100528095946.GB9774@csn.ul.ie>
Date:	Fri, 28 May 2010 10:59:47 +0100
From:	Mel Gorman <mel@....ul.ie>
To:	Doug Doan <dougd@...y.com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	andi@...stfloor.org, lee.schermerhorn@...com, rientjes@...gle.com,
	akpm@...ux-foundation.org
Subject: Re: [PATCH] hugetlb: call mmu notifiers on hugepage cow

On Thu, May 27, 2010 at 01:43:00PM -0700, Doug Doan wrote:
> From: Doug Doan <dougd@...y.com>
>
> When a copy-on-write occurs, we take one of two paths in handle_mm_fault: 
> through handle_pte_fault for normal pages, or through hugetlb_fault for 
> huge pages.
>
> In the normal page case, we eventually get to do_wp_page and call mmu 
> notifiers via ptep_clear_flush_notify. There is no callout to the mmmu 
> notifiers in the huge page case. This patch fixes that.
>
> Signed-off-by: Doug Doan <dougd@...y.com>
> ---

> --- mm/hugetlb.c.orig	2010-05-27 13:07:58.569546314 -0700
> +++ mm/hugetlb.c	2010-05-26 14:41:06.449296524 -0700
> @@ -2345,11 +2345,17 @@ retry_avoidcopy:
>  	ptep = huge_pte_offset(mm, address & huge_page_mask(h));
>  	if (likely(pte_same(huge_ptep_get(ptep), pte))) {
>  		/* Break COW */
> +		mmu_notifier_invalidate_range_start(mm,
> +			address & huge_page_mask(h),
> +			(address & huge_page_mask(h)) + huge_page_size(h));

Should the address not already be aligned?

Otherwise, I don't see any problem.

>  		huge_ptep_clear_flush(vma, address, ptep);
>  		set_huge_pte_at(mm, address, ptep,
>  				make_huge_pte(vma, new_page, 1));
>  		/* Make the old page be freed below */
>  		new_page = old_page;
> +		mmu_notifier_invalidate_range_end(mm,
> +			address & huge_page_mask(h),
> +			(address & huge_page_mask(h)) + huge_page_size(h));
>  	}
>  	page_cache_release(new_page);
>  	page_cache_release(old_page);


-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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