From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx162.postini.com [74.125.245.162]) by kanga.kvack.org (Postfix) with SMTP id 349B66B0005 for ; Mon, 25 Feb 2013 12:21:14 -0500 (EST) MIME-Version: 1.0 Message-ID: <622b6670-f311-40d5-9c8d-f5dd3e03633c@default> Date: Mon, 25 Feb 2013 09:20:55 -0800 (PST) From: Dan Magenheimer Subject: RE: Questin about swap_slot free and invalidate page References: <20130131051140.GB23548@blaptop> <20130204024950.GD2688@blaptop> <51236C11.1010208@gmail.com> <1f089254-3abe-4c63-a72a-c9e564ae7d0d@default> <51242F0D.4040201@gmail.com> <7793705b-a076-4c5a-be4d-9572d7560860@default> <5126E253.2030105@gmail.com> In-Reply-To: <5126E253.2030105@gmail.com> Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org List-ID: To: Ric Mason Cc: Minchan Kim , Hugh Dickins , Nitin Gupta , Seth Jennings , Konrad Rzeszutek Wilk , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton > From: Ric Mason [mailto:ric.masonn@gmail.com] > Subject: Re: Questin about swap_slot free and invalidate page >=20 > On 02/22/2013 05:42 AM, Dan Magenheimer wrote: > >> From: Ric Mason [mailto:ric.masonn@gmail.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@gmail.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 informatio= n 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. >=20 > 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? Yes, I have seen it. I am not sure of the exact circumstances when it happens as I am not an expert in the VFS subsystem. (Chris Mason wrote the VFS cleancache hooks in 2009.) Dan -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org