linux-kernel - Re: [PATCHv4 08/25] thp: support file pages in zap_huge

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Message-ID: <20160319010239.GB29883@node.shutemov.name>
Date:	Sat, 19 Mar 2016 04:02:40 +0300
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Cc:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Hugh Dickins <hughd@...gle.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dave Hansen <dave.hansen@...el.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Christoph Lameter <cl@...two.org>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Jerome Marchand <jmarchan@...hat.com>,
	Yang Shi <yang.shi@...aro.org>,
	Sasha Levin <sasha.levin@...cle.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCHv4 08/25] thp: support file pages in zap_huge_pmd()

On Fri, Mar 18, 2016 at 07:23:41PM +0530, Aneesh Kumar K.V wrote:
> "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com> writes:
> 
> > [ text/plain ]
> > split_huge_pmd() for file mappings (and DAX too) is implemented by just
> > clearing pmd entry as we can re-fill this area from page cache on pte
> > level later.
> >
> > This means we don't need deposit page tables when file THP is mapped.
> > Therefore we shouldn't try to withdraw a page table on zap_huge_pmd()
> > file THP PMD.
> 
> Archs like ppc64 use deposited page table to track the hardware page
> table slot information. We probably may want to add hooks which arch can
> use to achieve the same even with file THP 

Could you describe more on what kind of information you're talking about?

-- 
 Kirill A. Shutemov