linux-kernel - Re: [PATCHv2, RFC 00/30] Transparent huge page cache

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Date:	Mon, 18 Mar 2013 13:19:39 +0200 (EET)
From:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:	Simon Jeons <simon.jeons@...il.com>
Cc:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Hugh Dickins <hughd@...gle.com>,
	Wu Fengguang <fengguang.wu@...el.com>, Jan Kara <jack@...e.cz>,
	Mel Gorman <mgorman@...e.de>, linux-mm@...ck.org,
	Andi Kleen <ak@...ux.intel.com>,
	Matthew Wilcox <matthew.r.wilcox@...el.com>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	Hillf Danton <dhillf@...il.com>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCHv2, RFC 00/30] Transparent huge page cache

Simon Jeons wrote:
> On 03/18/2013 12:03 PM, Simon Jeons wrote:
> > Hi Kirill,
> > On 03/15/2013 01:50 AM, Kirill A. Shutemov wrote:
> >> From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
> >>
> >> Here's the second version of the patchset.
> >>
> >> The intend of the work is get code ready to enable transparent huge page
> >> cache for the most simple fs -- ramfs.
> >>
> >> We have read()/write()/mmap() functionality now. Still plenty work 
> >> ahead.
> >
> > One offline question.
> >
> > Why set PG_mlocked to page_tail which be splited in function 
> > __split_huge_page_refcount?

Not set, but copied from head page. Head page represents up-to-date sate
of compound page, we need to copy it to all tail pages on split.
 
> Also why can't find where _PAGE_SPLITTING and _PAGE_PSE flags are
> cleared in split_huge_page path?
 
The pmd is invalidated and replaced with reference to page table at the end
of __split_huge_page_map.
 
> Another offline question:
> Why don't clear tail page PG_tail flag in function
> __split_huge_page_refcount?

We do:

 page_tail->flags &= ~PAGE_FLAGS_CHECK_AT_PREP | __PG_HWPOISON;

-- 
 Kirill A. Shutemov
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