From: Geert Uytterhoeven <geert@linux-m68k.org>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Russell King - ARM Linux admin <linux@armlinux.org.uk>,
Linus Torvalds <torvalds@linux-foundation.org>,
Michal Hocko <mhocko@suse.com>, Rik van Riel <riel@surriel.com>,
Catalin Marinas <catalin.marinas@arm.com>,
kernel-team@fb.com, Dave Chinner <david@fromorbit.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Linux-MM <linux-mm@kvack.org>, Yafang Shao <laoar.shao@gmail.com>,
Al Viro <viro@zeniv.linux.org.uk>,
Johannes Weiner <hannes@cmpxchg.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Roman Gushchin <guro@fb.com>,
Linux ARM <linux-arm-kernel@lists.infradead.org>,
Kishon Vijay Abraham I <kishon@ti.com>,
Santosh Shilimkar <ssantosh@kernel.org>,
Chris Paterson <Chris.Paterson2@renesas.com>,
cip-dev@lists.cip-project.org
Subject: Re: [PATCH] vfs: keep inodes with page cache off the inode shrinker LRU
Date: Sat, 15 Feb 2020 12:25:32 +0100 [thread overview]
Message-ID: <CAMuHMdV8-=dj5n-FM1nHjXq1DhkJVOh4rLFxERt33jAQmU4h_A@mail.gmail.com> (raw)
In-Reply-To: <CAK8P3a3pzgVvwyDhHPoiSOqyv+h_ixbsdWMqG3sELenRJqFuew@mail.gmail.com>
Hi Arnd,
On Thu, Feb 13, 2020 at 5:54 PM Arnd Bergmann <arnd@arndb.de> wrote:
> On Wed, Feb 12, 2020 at 9:50 AM Russell King - ARM Linux admin
> <linux@armlinux.org.uk> wrote:
> > On Tue, Feb 11, 2020 at 05:03:02PM -0800, Linus Torvalds wrote:
> > > So at least my gut feel is that the arm people don't have any big
> > > reason to push for maintaining HIGHMEM support either.
> > >
> > > But I'm adding a couple of arm people and the arm list just in case
> > > they have some input.
> > >
> > > [ Obvious background for newly added people: we're talking about
> > > making CONFIG_HIGHMEM a deprecated feature and saying that if you want
> > > to run with lots of memory on a 32-bit kernel, you're doing legacy
> > > stuff and can use a legacy kernel ]
> >
> > Well, the recent 32-bit ARM systems generally have more than 1G
> > of memory, so make use of highmem as a rule. You're probably
> > talking about crippling support for any 32-bit ARM system produced
> > in the last 8 to 10 years.
>
> What I'm observing in the newly added board support is that memory
> configurations are actually going down, driven by component cost.
> 512MB is really cheap (~$4) these days with a single 256Mx16 DDR3
> chip or two 128Mx16. Going beyond 1GB is where things get expensive
> with either 4+ chips or LPDDR3/LPDDR4 memory.
>
> For designs with 1GB, we're probably better off just using
> CONFIG_VMSPLIT_3G_OPT (without LPAE) anyway, completely
> avoiding highmem. That is particularly true on systems with a custom
> kernel configuration.
>
> 2GB machines are less common, but are definitely important, e.g.
> MT6580 based Android phones and some industrial embedded machines
> that will live a long time. I've recently seen reports of odd behavior
> with CONFIG_VMSPLIT_2G and plus CONFIG_HIGHMEM and a 7:1
> ratio of lowmem to highmem that apparently causes OOM despite lots
> of lowmem being free. I suspect a lot of those workloads would still be
> better off with a CONFIG_VMSPLIT_2G_OPT (1.75 GB user, 2GB
> linear map). That config unfortunately has a few problems, too:
> - nobody has implemented it
> - it won't work with LPAE and therefore cannot support hardware
> that relies on high physical addresses for RAM or MMIO
> (those could run CONFIG_VMSPLIT_2G at the cost of wasting
> 12.5% of RAM).
> - any workload that requires the full 3GB of virtual address space won't
> work at all. This might be e.g. MAP_FIXED users, or build servers
> linking large binaries.
> It will take a while to find out what kinds of workloads suffer the most
> from a different vmsplit and what can be done to address that, but we
> could start by changing the kernel defconfig and distro builds to see
> who complains ;-)
>
> I think 32-bit ARM machines with 3GB or more are getting very rare,
> but some still exist:
> - The Armada XP development board had a DIMM slot that could take
> large memory (possibly up to 8GB with LPAE). This never shipped as
> a commercial product, but distro build servers sometimes still run on
> this, or on the old Calxeda or Keystone server systems.
> - a few early i.MX6 boards (e.g. HummingBoard) came had 4GB of
> RAM, though none of these seem to be available any more.
> - High-end phones from 2013/2014 had 3GB LPDDR3 before getting
> obsoleted by 64-bit phones. Presumably none of these ever ran
> Linux-4.x or newer.
> - My main laptop is a RK3288 based Chromebook with 4GB that just
> got updated to linux-4.19 by Google. Official updates apparently
> stop this summer, but it could easily run Debian later on.
> - Some people run 32-bit kernels on a 64-bit Raspberry Pi 4 or on
> arm64 KVM with lots of RAM. These should probably all
> migrate to 64-bit kernels with compat user space anyway.
> In theory these could also run on a VMSPLIT_4G_4G-like setup,
> but I don't think anyone wants to go there. Deprecating highmem
> definitely impacts any such users significantly, though staying on
> an LTS kernel may be an option if there are only few of them.
The CIP-supported RZ/G1 SoCs can have up to 4 GiB, typically split (even
for 1 GiB or 2 GiB configurations) in two parts, one below and one above
the 32-bit physical limit.
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
next prev parent reply other threads:[~2020-02-15 11:25 UTC|newest]
Thread overview: 58+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-11 17:55 [PATCH] vfs: keep inodes with page cache off the inode shrinker LRU Johannes Weiner
2020-02-11 18:20 ` Johannes Weiner
2020-02-11 19:05 ` Rik van Riel
2020-02-11 19:31 ` Johannes Weiner
2020-02-11 23:44 ` Andrew Morton
2020-02-12 0:28 ` Linus Torvalds
2020-02-12 0:47 ` Andrew Morton
2020-02-12 1:03 ` Linus Torvalds
2020-02-12 8:50 ` Russell King - ARM Linux admin
2020-02-13 9:50 ` Lucas Stach
2020-02-13 16:52 ` Arnd Bergmann
2020-02-15 11:25 ` Geert Uytterhoeven [this message]
2020-02-15 16:59 ` Arnd Bergmann
2020-02-16 9:44 ` Geert Uytterhoeven
2020-02-16 19:54 ` Chris Paterson
2020-02-16 20:38 ` Arnd Bergmann
2020-02-20 14:35 ` Chris Paterson
2020-02-26 18:04 ` santosh.shilimkar
2020-02-26 21:01 ` Arnd Bergmann
2020-02-26 21:11 ` santosh.shilimkar
2020-03-06 20:34 ` Nishanth Menon
2020-03-07 1:08 ` santosh.shilimkar
2020-03-08 10:58 ` Arnd Bergmann
2020-03-08 14:19 ` Russell King - ARM Linux admin
2020-03-09 13:33 ` Arnd Bergmann
2020-03-09 14:04 ` Russell King - ARM Linux admin
2020-03-09 15:04 ` Arnd Bergmann
2020-03-10 9:16 ` Michal Hocko
2020-03-09 15:59 ` Catalin Marinas
2020-03-09 16:09 ` Russell King - ARM Linux admin
2020-03-09 16:57 ` Catalin Marinas
2020-03-09 19:46 ` Arnd Bergmann
2020-03-11 14:29 ` Catalin Marinas
2020-03-11 16:59 ` Arnd Bergmann
2020-03-11 17:26 ` Catalin Marinas
2020-03-11 22:21 ` Arnd Bergmann
2020-02-12 3:58 ` Matthew Wilcox
2020-02-12 8:09 ` Michal Hocko
2020-02-17 13:31 ` Pavel Machek
2020-02-12 16:35 ` Johannes Weiner
2020-02-12 18:26 ` Andrew Morton
2020-02-12 18:52 ` Johannes Weiner
2020-02-12 12:25 ` Yafang Shao
2020-02-12 16:42 ` Johannes Weiner
2020-02-13 1:47 ` Yafang Shao
2020-02-13 13:46 ` Johannes Weiner
2020-02-14 2:02 ` Yafang Shao
2020-02-13 18:34 ` [PATCH v2] " Johannes Weiner
2020-02-14 16:53 ` [PATCH] " kbuild test robot
2020-02-14 21:30 ` kbuild test robot
2020-02-14 21:30 ` [PATCH] vfs: fix boolreturn.cocci warnings kbuild test robot
2020-05-12 21:29 ` [PATCH] vfs: keep inodes with page cache off the inode shrinker LRU Johannes Weiner
2020-05-13 1:32 ` Yafang Shao
2020-05-13 13:00 ` Johannes Weiner
2020-05-13 21:15 ` Andrew Morton
2020-05-14 11:27 ` Johannes Weiner
2020-05-14 2:24 ` Andrew Morton
2020-05-14 10:37 ` Johannes Weiner
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