Arndale uses 2G/2G memory split

[Ard Biesheuvel]

Currently, the default kernel configurations for Arndale divide the virtual memory space into 2 GB for the kernel and 2G for userland, while the usual split is 3G/1G. This significantly reduces the usable space not just for random access memory but also for userland mmap(), which is potentially a concern when benchmarking server grade applications like web servers and databases.

Please revert to using the default memory split of 3G/1G

[Fathi Boudra (fboudra)]

Tushar, any comments?

[Andrey Konovalov (andrey-konovalov)]

Tushar, if there is a fix before, say, Monday, I could add it to 13.05 linux-linaro release. Thanks!

[Tushar Behera (tusharbehera)]

It was suggested by Leif [1] that there is a significant system performance gain with 2G/2G memory split. I would like to get his views on this.

[1] https://git.linaro.org/gitweb?p=landing-teams/working/samsung/kernel.git;a=commit;h=12d1b1afc0a2c5378917894059a7a1d9d646496c

[Tushar Behera (tusharbehera)]

Reference: https://bugs.launchpad.net/linaro-landing-team-samsung/+bug/1163321

[Leif Lindholm (leif-lindholm)]

The issue is with the fact that the Arndale UEFI port resides in the second GB of RAM, making it "highmem" - which causes more than a little bit of pain with runtime services and ACPI initialisation. I will discuss with Ard offline and update later.

[Ard Biesheuvel (ard-biesheuvel)]

Leif and I agree that 3g/1g is more suitable in general, but in this particular case, the ability to access kernel directly mapped memory above 1GB is essential for Leif's UEFI work, so let's put this on hold for now.

[Fathi Boudra (fboudra)]

In that case, I would prefer to have a sane default (3g/1g) and set up a specific build for Leif's work with 2g/2g memory split.

[Leif Lindholm (leif-lindholm)]

It isn't just for my work. It is for anyone wanting to use any of my work (EFI runtime services, GRUB).

3/1 is a sane default for platforms that either:
- Don't use UEFI.
or
- Place UEFI within the first GB of RAM.

The latter is not true for Arndale, so until we have a way to work around this, 2/2 is the sane default for that platform.

[Fathi Boudra (fboudra)]

Fair enough. Closing as wontfix.