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

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Date:	Mon, 18 Mar 2013 19:29:20 +0800
From:	Simon Jeons <simon.jeons@...il.com>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
CC:	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

Hi Kirill,
On 03/18/2013 07:19 PM, Kirill A. Shutemov wrote:
> 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.

I always see up-to-date state, could you conclude to me which state can 
be treated as up-to-date? :-)

>   
>> 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.

Since pmd is populated by page table and new flag why need 
invalidated(clear present flag) before it?

>   
>> 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;
>

Got it.
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