linux-kernel - Re: [PATCH v12 02/11] mm, swap: Add infrastructure for saving page metadata on swap

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Message-ID: <d807ba68-decd-e195-f607-ef6962e40c96@linux.intel.com>
Date:   Mon, 5 Mar 2018 11:35:42 -0800
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     Khalid Aziz <khalid.aziz@...cle.com>, akpm@...ux-foundation.org,
        davem@...emloft.net, arnd@...db.de
Cc:     kirill.shutemov@...ux.intel.com, mhocko@...e.com,
        ross.zwisler@...ux.intel.com, dave.jiang@...el.com,
        mgorman@...hsingularity.net, willy@...radead.org, hughd@...gle.com,
        minchan@...nel.org, hannes@...xchg.org, shli@...com,
        mingo@...nel.org, jglisse@...hat.com, me@...in.cc,
        anthony.yznaga@...cle.com, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        sparclinux@...r.kernel.org, Khalid Aziz <khalid@...ehiking.org>
Subject: Re: [PATCH v12 02/11] mm, swap: Add infrastructure for saving page
 metadata on swap

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?