linux-kernel - Re: Questin about swap_slot free and invalidate page

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Date:	Fri, 22 Feb 2013 11:13:23 +0800
From:	Ric Mason <ric.masonn@...il.com>
To:	Dan Magenheimer <dan.magenheimer@...cle.com>
CC:	Minchan Kim <minchan@...nel.org>, Hugh Dickins <hughd@...gle.com>,
	Nitin Gupta <ngupta@...are.org>,
	Seth Jennings <sjenning@...ux.vnet.ibm.com>,
	Konrad Rzeszutek Wilk <konrad@...nok.org>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: Questin about swap_slot free and invalidate page

On 02/22/2013 05:42 AM, Dan Magenheimer wrote:
>> From: Ric Mason [mailto:ric.masonn@...il.com]
>> Subject: Re: Questin about swap_slot free and invalidate page
>>
>> On 02/19/2013 11:27 PM, Dan Magenheimer wrote:
>>>> From: Ric Mason [mailto:ric.masonn@...il.com]
>>>>> Hugh is right that handling the possibility of duplicates is
>>>>> part of the tmem ABI.  If there is any possibility of duplicates,
>>>>> the ABI defines how a backend must handle them to avoid data
>>>>> coherency issues.
>>>>>
>>>>> The kernel implements an in-kernel API which implements the tmem
>>>>> ABI.  If the frontend and backend can always agree that duplicate
>>>> Which ABI in zcache implement that?
>>> https://oss.oracle.com/projects/tmem/dist/documentation/api/tmemspec-v001.pdf
>>>
>>> The in-kernel APIs are frontswap and cleancache.  For more information about
>>> tmem, see http://lwn.net/Articles/454795/
>> But you mentioned that you have in-kernel API which can handle
>> duplicate.  Do you mean zcache_cleancache/frontswap_put_page? I think
>> they just overwrite instead of optional flush the page on the
>> second(duplicate) put as mentioned in your tmemspec.
> Maybe I am misunderstanding your question...  The spec allows
> overwrite (and return success) OR flush the page (and return
> failure).  Zcache does the latter (flush).  The code that implements
> it is in tmem_put.

Thanks for your point out.  Pers pages can have duplicate put since swap 
cache page can be reused. Can eph pages also have duplicate put? If yes, 
when can happen?

>

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