linux-kernel - Re: [PATCH 1/1] hugetlbfs: handle pages higher order than MAX

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Message-Id: <200810082329.59561.nickpiggin@yahoo.com.au>
Date:	Wed, 8 Oct 2008 23:29:59 +1100
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Andy Whitcroft <apw@...dowen.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Jon Tollefson <kniht@...ux.vnet.ibm.com>,
	Mel Gorman <mel@....ul.ie>
Subject: Re: [PATCH 1/1] hugetlbfs: handle pages higher order than MAX_ORDER

On Wednesday 08 October 2008 20:33, Andy Whitcroft wrote:
> When working with hugepages, hugetlbfs assumes that those hugepages
> are smaller than MAX_ORDER.  Specifically it assumes that the mem_map
> is contigious and uses that to optimise access to the elements of the
> mem_map that represent the hugepage.  Gigantic pages (such as 16GB pages
> on powerpc) by definition are of greater order than MAX_ORDER (larger
> than MAX_ORDER_NR_PAGES in size).  This means that we can no longer make
> use of the buddy alloctor guarentees for the contiguity of the mem_map,
> which ensures that the mem_map is at least contigious for maximmally
> aligned areas of MAX_ORDER_NR_PAGES pages.
>
> This patch adds new mem_map accessors and iterator helpers which handle
> any discontiguity at MAX_ORDER_NR_PAGES boundaries.  It then uses these
> within copy_huge_page, clear_huge_page, and follow_hugetlb_page to allow
> these to handle gigantic pages.
>
> Signed-off-by: Andy Whitcroft <apw@...dowen.org>

Seems good to me... but do you have to add lots of stuff into the end of
the for statements? Why not just at the end of the block?
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