linux-kernel - Re: [PATCHv9 32/36] thp: reintroduce split_huge

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Date:	Fri, 31 Jul 2015 17:13:38 +0200
From:	Jerome Marchand <jmarchan@...hat.com>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Hugh Dickins <hughd@...gle.com>
CC:	Dave Hansen <dave.hansen@...el.com>, Mel Gorman <mgorman@...e.de>,
	Rik van Riel <riel@...hat.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Christoph Lameter <cl@...two.org>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Steve Capper <steve.capper@...aro.org>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...e.cz>,
	Sasha Levin <sasha.levin@...cle.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCHv9 32/36] thp: reintroduce split_huge_page()

On 07/20/2015 04:21 PM, Kirill A. Shutemov wrote:
> This patch adds implementation of split_huge_page() for new
> refcountings.
> 
> Unlike previous implementation, new split_huge_page() can fail if
> somebody holds GUP pin on the page. It also means that pin on page
> would prevent it from bening split under you. It makes situation in
> many places much cleaner.
> 
> The basic scheme of split_huge_page():
> 
>   - Check that sum of mapcounts of all subpage is equal to page_count()
>     plus one (caller pin). Foll off with -EBUSY. This way we can avoid
>     useless PMD-splits.
> 
>   - Freeze the page counters by splitting all PMD and setup migration
>     PTEs.
> 
>   - Re-check sum of mapcounts against page_count(). Page's counts are
>     stable now. -EBUSY if page is pinned.
> 
>   - Split compound page.
> 
>   - Unfreeze the page by removing migration entries.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Tested-by: Sasha Levin <sasha.levin@...cle.com>
> Tested-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>

Acked-by: Jerome Marchand <jmarchan@...hat.com>

> ---
>  include/linux/huge_mm.h |   7 +-
>  include/linux/pagemap.h |  13 +-
>  mm/huge_memory.c        | 318 ++++++++++++++++++++++++++++++++++++++++++++++++
>  mm/internal.h           |  26 +++-
>  mm/rmap.c               |  21 ----
>  5 files changed, 357 insertions(+), 28 deletions(-)
> 
> 



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