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From: Arnd Bergmann <arnd@kernel.org>
To: Max Filippov <jcmvbkbc@gmail.com>
Cc: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>,
	Linus Walleij <linus.walleij@linaro.org>,
	Gerhard Pircher <gerhard_pircher@gmx.net>,
	Arnd Bergmann <arnd@arndb.de>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	linux-m68k <linux-m68k@lists.linux-m68k.org>,
	Sparc kernel list <sparclinux@vger.kernel.org>,
	Linux-sh list <linux-sh@vger.kernel.org>
Subject: Re: Old platforms: bring out your dead
Date: Fri, 15 Jan 2021 09:31:53 +0100
Message-ID: <CAK8P3a16dta82GOVZCcMgFokB4Mo6y6Vje=+5gUH-t-1ATQYUw@mail.gmail.com> (raw)
In-Reply-To: <CAMo8Bf+geJqaaTkwaRyMUZPJgGC1ELXTdnYGq92UNnaaz2CFVg@mail.gmail.com>

On Fri, Jan 15, 2021 at 12:09 AM Max Filippov <jcmvbkbc@gmail.com> wrote:
> On Thu, Jan 14, 2021 at 1:25 PM Arnd Bergmann <arnd@kernel.org> wrote:
> > | arch/mips/Kconfig:config HIGHMEM
> > | arch/xtensa/Kconfig:config HIGHMEM
> >
> > AFAICT On MIPS (prior to MIPS32r3) and xtensa, you have at
> > most 512MB in the linear map, so the VMSPLIT_2G or VMSPLIT_4G_4G
> > tricks won't work.
>
> Regarding xtensa this was done to minimize difference between
> MMUv2 and MMUv3 virtual memory layouts. MMUv2 has been
> obsoleted more than 10 years ago, and MMUv3 is much more
> flexible and can do e.g. 4GB linear map. The only piece of xtensa
> MMUv2 hardware that I have has 96MB of DRAM which fits into
> its linear mapping. So maybe it's time to do a cleanup and
> rearrange virtual memory layout to eliminate the need of highmem.

Yes, I think that sounds like a useful preparation for the future.

> > I have no idea who uses xtensa systems with lots of memory on
> > modern kernels.
>
> We definitely use it for development internally at Cadence/Tensilica,
> mainly on simulators, but also on FPGA boards (e.g. on KC705 we
> can use all of the 1GB onboard DRAM).
> In the last few years we've had a few support requests for linux on
> xtensa cores with MMU, but AFAICT none of them had to deal with
> more than 512MB of onboard memory.

If 1GB of RAM is a useful upper bound on MMUv3, the easiest way is
probably to hardcode the CONFIG_VMSPLIT_3G_OPT behavior
from x86 and ARM, using 2.75GB of user addresses (TASK_SIZE),
and 1.25 GB that gets split between linear map and vmalloc space,
but no uncached linear map and ioremap() pointing into vmalloc
instead. If you want to be prepared for machines with 2GB of linear
lowmem, you could do the same with VMSPLIT_2G_OPT
(TASK_SIZE == 0x70000000).

      Arnd

  reply index

Thread overview: 121+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-08 22:55 Arnd Bergmann
2021-01-08 23:32 ` Steven Rostedt
2021-01-09 22:04   ` Arnd Bergmann
2021-01-08 23:44 ` Thomas Bogendoerfer
2021-01-09  0:16 ` Linus Walleij
2021-01-09 17:32   ` Florian Fainelli
2021-01-09 21:59   ` Arnd Bergmann
2021-01-09  5:56 ` Willy Tarreau
2021-01-09 21:52   ` Arnd Bergmann
2021-01-10  6:21     ` Willy Tarreau
2021-01-10 10:44       ` Russell King - ARM Linux admin
2021-01-11  9:50     ` David Laight
2021-01-13 10:27       ` Andy Shevchenko
2021-01-13 12:02         ` Linus Walleij
2021-01-13 12:17           ` Andy Shevchenko
2021-01-13 12:21             ` Andy Shevchenko
2021-01-15  0:03               ` Bernd Petrovitsch
2021-01-15  0:24                 ` William Breathitt Gray
2021-01-15  8:59                   ` David Laight
2021-01-13 12:30           ` William Breathitt Gray
2021-01-13 12:56             ` William Breathitt Gray
2021-01-13 13:44           ` Arnd Bergmann
2021-02-04 21:01         ` Pavel Machek
2021-02-05  9:13           ` David Laight
2021-02-05  9:29             ` Pavel Machek
2021-01-09 17:34 ` Florian Fainelli
2021-01-09 21:18   ` Arnd Bergmann
2021-01-09 17:43 ` Russell King - ARM Linux admin
2021-01-09 21:34   ` Arnd Bergmann
2021-01-11 20:09     ` Russell King - ARM Linux admin
2021-01-09 20:19 ` Baruch Siach
2021-01-09 21:19   ` Arnd Bergmann
     [not found] ` <67171E13-6786-4B44-A8C2-3302963B055F@gmail.com>
2021-01-09 22:20   ` Arnd Bergmann
2021-01-10 18:12     ` Fabian Vogt
2021-01-10 19:20       ` Arnd Bergmann
2021-01-10 21:33       ` Linus Walleij
2021-01-11  0:33         ` Russell King - ARM Linux admin
2021-01-11 12:32           ` Arnd Bergmann
2021-01-11 12:36             ` Russell King - ARM Linux admin
2021-01-09 23:12 ` Andrew Lunn
2021-01-10  8:45   ` Arnd Bergmann
2021-01-10 16:46     ` Andrew Lunn
2021-01-10 17:27       ` Arnd Bergmann
2021-01-10 19:51         ` Andrew Lunn
2021-01-10 15:51 ` Neil Armstrong
2021-01-10 15:56   ` Arnd Bergmann
2021-01-10 17:35 ` John Paul Adrian Glaubitz
2021-01-10 21:46   ` Sam Ravnborg
2021-01-11  8:05     ` John Paul Adrian Glaubitz
2021-01-11 14:55       ` chase rayfield
2021-01-12  0:26         ` Rob Landley
2021-01-12  0:50           ` chase rayfield
2021-01-12 14:37         ` John Paul Adrian Glaubitz
2021-01-11 18:09     ` Rob Landley
2021-01-11 15:04   ` Gerhard Pircher
2021-01-12 14:44     ` John Paul Adrian Glaubitz
2021-01-12 22:46       ` Linus Walleij
2021-01-13  8:09         ` Rob Landley
2021-01-13  8:21           ` Geert Uytterhoeven
2021-01-13 13:25             ` Rob Landley
2021-01-13 12:02           ` Andy Shevchenko
2021-01-13  8:15         ` Geert Uytterhoeven
2021-01-13 10:39         ` Arnd Bergmann
2021-01-14  3:54           ` New platforms: bring out your dead, was " Finn Thain
2021-01-14  9:41         ` John Paul Adrian Glaubitz
2021-01-14  9:48           ` Geert Uytterhoeven
2021-01-14 21:21           ` Arnd Bergmann
2021-01-14 22:54             ` Undesirable code, was Re: Old platforms etc Finn Thain
2021-01-14 23:09             ` Old platforms: bring out your dead Max Filippov
2021-01-15  8:31               ` Arnd Bergmann [this message]
2021-01-13  0:12       ` Old platforms never die, was " Finn Thain
2021-01-16  6:54         ` Rob Landley
2021-01-16 23:22           ` Finn Thain
2021-01-13 11:47       ` Andy Shevchenko
2021-01-11  1:39 ` Daniel Palmer
2021-01-11  9:15   ` John Paul Adrian Glaubitz
2021-01-11  9:20     ` Geert Uytterhoeven
2021-01-11  9:26       ` John Paul Adrian Glaubitz
2021-01-11  9:36         ` Geert Uytterhoeven
2021-01-11  9:50           ` Greg Ungerer
2021-01-11  9:42     ` Daniel Palmer
2021-01-11 10:13   ` Arnd Bergmann
2021-01-11  8:19 ` Geert Uytterhoeven
2021-01-11  8:59   ` Arnd Bergmann
2021-01-11  9:16     ` Geert Uytterhoeven
2021-01-11 10:28       ` Geert Uytterhoeven
2021-01-11 10:37         ` Arnd Bergmann
2021-01-11  9:40     ` Thomas Bogendoerfer
2021-01-11 10:34       ` Arnd Bergmann
2021-01-11  8:40 ` efm32 is dead [Was: Old platforms: bring out your dead] Uwe Kleine-König
2021-01-11 11:10 ` Old platforms: bring out your dead Viresh Kumar
2021-01-11 19:59   ` Arnd Bergmann
2021-01-11 21:15     ` Mattias Wallin
2021-01-11 21:47       ` Arnd Bergmann
2021-01-11 13:13 ` Marc Gonzalez
2021-01-11 17:29   ` Måns Rullgård
2021-01-11 21:50     ` Arnd Bergmann
2021-01-12  8:23       ` Marc Gonzalez
2021-01-11 14:22 ` Mark Salter
2021-01-11 15:00   ` Arnd Bergmann
2021-01-11 14:44 ` Alexander Shiyan
2021-01-11 14:58   ` Arnd Bergmann
2021-01-11 16:23 ` Sylvain Lemieux
2021-01-11 22:17   ` Alexandre Belloni
2021-01-11 19:58 ` Thomas Petazzoni
2021-01-11 20:10   ` Arnd Bergmann
2021-01-11 20:25 ` Song Bao Hua (Barry Song)
2021-01-12  8:41   ` Marc Gonzalez
2021-01-13 10:30 ` Andy Shevchenko
2021-01-13 11:02   ` Arnd Bergmann
2021-01-13 16:14 ` [v2] " Arnd Bergmann
2021-01-13 19:00   ` Krzysztof Hałasa
2021-01-14  8:51     ` Arnd Bergmann
2021-01-15  7:08   ` Wei Xu
2021-01-15  9:26     ` Arnd Bergmann
2021-01-15 11:09       ` Leizhen (ThunderTown)
2021-01-15 12:04         ` Arnd Bergmann
2021-01-18 10:46           ` Wei Xu
2021-01-13 22:27 ` Richard Z
2021-02-05 13:37 ` Alexander Lobakin
2021-01-12  2:05 tedheadster

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