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Subject: Re: [PATCH v12 02/11] mm, swap: Add infrastructure for saving page
 metadata on swap
To: Khalid Aziz <khalid.aziz@oracle.com>, akpm@linux-foundation.org,
        davem@davemloft.net, arnd@arndb.de
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        Khalid Aziz <khalid@gonehiking.org>
From: Dave Hansen <dave.hansen@linux.intel.com>
Message-ID: <d807ba68-decd-e195-f607-ef6962e40c96@linux.intel.com>
Date: Mon, 5 Mar 2018 11:35:42 -0800
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On 03/05/2018 11:29 AM, Khalid Aziz wrote:
> ADI data is per page data and is held in the spare bits in the RAM. It
> is loaded into the cache when data is loaded from RAM and flushed out to
> spare bits in the RAM when data is flushed from cache. Sparc allows one
> tag for each ADI block size of data and ADI block size is same as
> cacheline size.

Which does not square with your earlier assertion "ADI data is per page
data".  It's per-cacheline data.  Right?

> When a page is loaded into RAM from swap space, all of
> the associated ADI data for the page must also be loaded into the RAM,
> so it looks like page level data and storing it in page level software
> data structure makes sense. I am open to other suggestions though.

Do you have a way to tell that data is not being thrown away?  Like if
the ADI metadata is different for two different cachelines within a
single page?