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Date: Tue, 16 Feb 2016 13:00:23 +0300
From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Subject: Re: [PATCHv2 13/28] thp: support file pages in zap_huge_pmd()
Message-ID: <20160216100023.GC46557@black.fi.intel.com>
References: <1455200516-132137-1-git-send-email-kirill.shutemov@linux.intel.com>
 <1455200516-132137-14-git-send-email-kirill.shutemov@linux.intel.com>
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To: Dave Hansen <dave.hansen@intel.com>
Cc: Hugh Dickins <hughd@google.com>, Andrea Arcangeli <aarcange@redhat.com>, Andrew Morton <akpm@linux-foundation.org>, Vlastimil Babka <vbabka@suse.cz>, Christoph Lameter <cl@gentwo.org>, Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>, Jerome Marchand <jmarchan@redhat.com>, Yang Shi <yang.shi@linaro.org>, Sasha Levin <sasha.levin@oracle.com>, linux-kernel@vger.kernel.org, linux-mm@kvack.org

On Fri, Feb 12, 2016 at 10:33:37AM -0800, Dave Hansen wrote:
> On 02/11/2016 06:21 AM, Kirill A. Shutemov wrote:
> > For file pages we don't deposit page table on mapping: no need to
> > withdraw it.
> 
> I thought the deposit thing was to guarantee we could always do a PMD
> split.  It still seems like if you wanted to split a huge-tmpfs page,
> you'd need to first split the PMD which might need the deposited one.
> 
> Why not?

For file thp, split_huge_pmd() is implemented by clearing out the pmd: we
can setup and fill pte table later. Therefore no need to deposit page
table -- we would not use it. DAX does the same.

-- 
 Kirill A. Shutemov

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