linux-kernel - Re: [PATCHv2 17/28] thp: skip file huge pmd on copy_huge

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Message-ID: <20160216101450.GE46557@black.fi.intel.com>
Date:	Tue, 16 Feb 2016 13:14:50 +0300
From:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:	Dave Hansen <dave.hansen@...el.com>
Cc:	Hugh Dickins <hughd@...gle.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	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
Subject: Re: [PATCHv2 17/28] thp: skip file huge pmd on copy_huge_pmd()

On Fri, Feb 12, 2016 at 10:42:09AM -0800, Dave Hansen wrote:
> On 02/11/2016 06:21 AM, Kirill A. Shutemov wrote:
> > File pmds can be safely skip on copy_huge_pmd(), we can re-fault them
> > later. COW for file mappings handled on pte level.
> 
> Is this different from 4k pages?  I figured we might skip copying
> file-backed ptes on fork, but I couldn't find the code.

Currently, we only filter out on per-VMA basis. See first comment in
copy_page_range().

Here we handle PMD mapped file pages in COW mapping. File THP can be
mapped into COW mapping as result of read page fault.

-- 
 Kirill A. Shutemov