Re: [PATCH v1] mips/mips_malta: Allow more than 2G RAM

From: Aurelien Jarno <aurelien@aurel32.net>
To: "Philippe Mathieu-Daudé" <philmd@redhat.com>
Cc: Paul Burton <pburton@wavecomp.com>,
	Peter Maydell <peter.maydell@linaro.org>,
	Yunqiang Su <ysu@wavecomp.com>,
	QEMU Developers <qemu-devel@nongnu.org>,
	Jiaxun Yang <jiaxun.yang@flygoat.com>,
	Paul Burton <paul.burton@mips.com>,
	Aleksandar Markovic <amarkovic@wavecomp.com>,
	Igor Mammedov <imammedo@redhat.com>,
	Aleksandar Markovic <aleksandar.m.mail@gmail.com>
Subject: Re: [PATCH v1] mips/mips_malta: Allow more than 2G RAM
Date: Mon, 23 Mar 2020 17:35:45 +0100	[thread overview]
Message-ID: <20200323163545.GA19598@aurel32.net> (raw)
In-Reply-To: <d9f08408-9c1e-36d9-869b-bac250c6f027@redhat.com>

Hi,

Sorry for the delay, I just want to give some more details about the
Debian.

On 2020-03-14 10:09, Philippe Mathieu-Daudé wrote:
> IIUC today all distributions supporting MIPS ports are building their MIPS
> packages on QEMU instances because it is faster than the native MIPS
> hardware they have.

Actually Debian requires that packages are built on real hardware. We
have a mix of Loongson 3 and Octeon 3 based build daemons. They all have
8GiB of RAM.

> Since one (or two?) years, some binaries (Linux kernel? QEMU?) are failing
> to link because the amount of guest memory is restricted to 2GB (probably
> advance of linker techniques, now linkers use more memory).

The problem happens with big packages (e.g. ceph which is a dependency
of QEMU). The problem is not the physical memory issue, but the virtual
address space, which is limited to 2GB for 32-bit processes. That's why
we do not have the issue for the 64-bit ports.

> YunQiang, is this why you suggested this change?
> 
> See:
> - https://www.mail-archive.com/debian-mips@lists.debian.org/msg10912.html
> - https://alioth-lists.debian.net/pipermail/pkg-rust-maintainers/2019-January/004844.html
> 
> I believe most of the QEMU Malta board users don't care it is a Malta board,
> they only care it is a fast emulated MIPS machine.
> Unfortunately it is the default board.
> 
> However 32-bit MIPS port is being dropped on Debian:
> https://lists.debian.org/debian-mips/2019/07/msg00010.html

The 32-bit big endian port has been dropped after the Buster (10)
release and won't be available for the Bullseye release (11). The
32-bit little endian port is still available, but it's difficult to keep
it alive given the 2GB limit.

> Maybe we can sync with the Malta users, ask them to switch to the Boston
> machines to build 64-bit packages, then later reduce the Malta board to 1GB.
> (The Boston board is more recent, but was not available at the time users
> started to use QEMU to build 64-bit packages).
> 
> Might it be easier starting introducing a malta-5.0 machine restricted to
> 1GB?

In any case having an easy way to simulate machines with more than 2GB
of RAM in QEMU would be great.

Cheers,
Aurelien

-- 
Aurelien Jarno                          GPG: 4096R/1DDD8C9B
aurelien@aurel32.net                 http://www.aurel32.net