linux-kernel - Re: [PATCHv5 05/28] mm: adjust FOLL

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Date:	Fri, 15 May 2015 14:36:46 +0300
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	Vlastimil Babka <vbabka@...e.cz>
Cc:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Hugh Dickins <hughd@...gle.com>,
	Dave Hansen <dave.hansen@...el.com>,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	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>,
	Jerome Marchand <jmarchan@...hat.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCHv5 05/28] mm: adjust FOLL_SPLIT for new refcounting

On Fri, May 15, 2015 at 01:05:27PM +0200, Vlastimil Babka wrote:
> On 04/23/2015 11:03 PM, Kirill A. Shutemov wrote:
> >We need to prepare kernel to allow transhuge pages to be mapped with
> >ptes too. We need to handle FOLL_SPLIT in follow_page_pte().
> >
> >Also we use split_huge_page() directly instead of split_huge_page_pmd().
> >split_huge_page_pmd() will gone.
> 
> You still call split_huge_page_pmd() for the is_huge_zero_page(page) case.

For huge zero page we split PMD into table of zero pages and don't touch
compound page under it. That's what split_huge_page_pmd() (renamed into
split_huge_pmd()) will do by the end of patchset.

> Also, of the code around split_huge_page() you basically took from
> split_huge_page_pmd() and open-coded into follow_page_mask(), you didn't
> include the mmu notifier calls. Why are they needed in split_huge_page_pmd()
> but not here?

We do need mmu notifier in split_huge_page_pmd() for huge zero page. When
we need to split compound page we go into split_huge_page() which takes
care about mmut notifiers.

-- 
 Kirill A. Shutemov
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