From: Dan Magenheimer <dan.magenheimer@oracle.com>
To: Ric Mason <ric.masonn@gmail.com>
Cc: Minchan Kim <minchan@kernel.org>, Hugh Dickins <hughd@google.com>,
Nitin Gupta <ngupta@vflare.org>,
Seth Jennings <sjenning@linux.vnet.ibm.com>,
Konrad Rzeszutek Wilk <konrad@darnok.org>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Andrew Morton <akpm@linux-foundation.org>
Subject: RE: Questin about swap_slot free and invalidate page
Date: Mon, 25 Feb 2013 09:20:55 -0800 (PST) [thread overview]
Message-ID: <622b6670-f311-40d5-9c8d-f5dd3e03633c@default> (raw)
In-Reply-To: <5126E253.2030105@gmail.com>
> From: Ric Mason [mailto:ric.masonn@gmail.com]
> 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@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 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?
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
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prev parent reply other threads:[~2013-02-25 17:21 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-01-31 5:11 Questin about swap_slot free and invalidate page Minchan Kim
2013-02-04 1:51 ` Hugh Dickins
2013-02-04 2:49 ` Minchan Kim
2013-02-04 21:28 ` Dan Magenheimer
2013-02-05 1:24 ` Minchan Kim
2013-02-19 12:12 ` Ric Mason
2013-02-19 15:27 ` Dan Magenheimer
2013-02-20 2:03 ` Ric Mason
2013-02-21 21:42 ` Dan Magenheimer
2013-02-22 3:13 ` Ric Mason
2013-02-25 17:20 ` Dan Magenheimer [this message]
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