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

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Date:	Mon, 18 Mar 2013 19:42:34 +0800
From:	Ric Mason <ric.masonn@...il.com>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
CC:	Simon Jeons <simon.jeons@...il.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

On 03/18/2013 07:42 PM, Kirill A. Shutemov wrote:
> Simon Jeons wrote:
>> 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? :-)
> While we work with huge page we only alter flags (like mlocked or
> uptodate) of head page, but not tail, so we have to copy flags to all tail
> pages on split. We also need to distribute _count and _mapcount properly.
> Just read the code.

Sorry, you can treat this question as an offline one and irrelevant thp. 
Which state of page 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?
> Comment just before pmdp_invalidate() in __split_huge_page_map() is fairly
> informative.
>

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