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Date: Thu, 21 Feb 2013 13:42:21 -0800 (PST)
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>,
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        linux-kernel@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>
Subject: RE: Questin about swap_slot free and invalidate page
References: <20130131051140.GB23548@blaptop>
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> 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.