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

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Message-ID: <0d77dc3c-1454-a689-a0fb-f07e8973c29e@linux.intel.com>
Date:   Mon, 5 Mar 2018 11:20:09 -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 02/21/2018 09:15 AM, Khalid Aziz wrote:
> If a processor supports special metadata for a page, for example ADI
> version tags on SPARC M7, this metadata must be saved when the page is
> swapped out. The same metadata must be restored when the page is swapped
> back in. This patch adds two new architecture specific functions -
> arch_do_swap_page() to be called when a page is swapped in, and
> arch_unmap_one() to be called when a page is being unmapped for swap
> out. These architecture hooks allow page metadata to be saved if the
> architecture supports it.

I still think silently squishing cacheline-level hardware data into
page-level software data structures is dangerous.

But, you seem rather determined to do it this way.  I don't think this
will _hurt_ anyone else, though other than needlessly cluttering up the
code.