linux-kernel - Re: [PATCH v2 00/13] arch, mm: deprecate DISCONTIGMEM

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Message-ID: <20201117062316.GB370813@kernel.org>
Date:   Tue, 17 Nov 2020 08:23:16 +0200
From:   Mike Rapoport <rppt@...nel.org>
To:     John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Greg Ungerer <gerg@...ux-m68k.org>,
        Jonathan Corbet <corbet@....net>,
        Matt Turner <mattst88@...il.com>, Meelis Roos <mroos@...ux.ee>,
        Michael Schmitz <schmitzmic@...il.com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Russell King <linux@...linux.org.uk>,
        Tony Luck <tony.luck@...el.com>,
        Vineet Gupta <vgupta@...opsys.com>,
        Will Deacon <will@...nel.org>, linux-alpha@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-doc@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-ia64@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-m68k@...ts.linux-m68k.org,
        linux-mm@...ck.org, linux-snps-arc@...ts.infradead.org
Subject: Re: [PATCH v2 00/13] arch, mm: deprecate DISCONTIGMEM

Hi Adrian,

On Tue, Nov 17, 2020 at 06:24:51AM +0100, John Paul Adrian Glaubitz wrote:
> Hi!
> 
> On 11/1/20 6:04 PM, Mike Rapoport wrote:
> > It's been a while since DISCONTIGMEM is generally considered deprecated,
> > but it is still used by four architectures. This set replaces DISCONTIGMEM
> > with a different way to handle holes in the memory map and marks
> > DISCONTIGMEM configuration as BROKEN in Kconfigs of these architectures with
> > the intention to completely remove it in several releases.
> > 
> > While for 64-bit alpha and ia64 the switch to SPARSEMEM is quite obvious
> > and was a matter of moving some bits around, for smaller 32-bit arc and
> > m68k SPARSEMEM is not necessarily the best thing to do.
> > 
> > On 32-bit machines SPARSEMEM would require large sections to make section
> > index fit in the page flags, but larger sections mean that more memory is
> > wasted for unused memory map.
> > 
> > Besides, pfn_to_page() and page_to_pfn() become less efficient, at least on
> > arc.
> > 
> > So I've decided to generalize arm's approach for freeing of unused parts of
> > the memory map with FLATMEM and enable it for both arc and m68k. The
> > details are in the description of patches 10 (arc) and 13 (m68k).
> 
> Apologies for the late reply. Is this still relevant for testing?
> 
> I have already successfully tested v1 of the patch set, shall I test v2?

There were minor differences only for m68k between the versions. I've
verified them on ARAnyM but if you have a real machine a run there would
be nice.

> Adrian
> 
> -- 
>  .''`.  John Paul Adrian Glaubitz
> : :' :  Debian Developer - glaubitz@...ian.org
> `. `'   Freie Universitaet Berlin - glaubitz@...sik.fu-berlin.de
>   `-    GPG: 62FF 8A75 84E0 2956 9546  0006 7426 3B37 F5B5 F913
> 
> 

-- 
Sincerely yours,
Mike.