On Mon, 18 Mar 2019, Mike Rapoport wrote: > On Sat, Mar 16, 2019 at 04:55:30AM +0530, Anup Patel wrote: > > > We started exploring ways to re-claim memory below kernel because > > we are trying to get Linux working on Kendryte K210 board > > (https://kendryte.com/). This board has dual-core 64bit RISC-V but it > > only has 8MB RAM. > > Huh, 8MB of RAM is tough... > > It is possible to use the memory below the kernel, e.g x86-64 does that. > But it is definitely a separate change and with such RAM diet using 4K > pages seems unavoidable. > > I still have concern about using 4K pages whenever the load address is not > 2M (4M) aligned. People tend to not pay enough attention to such details > and they would load the kernel at an arbitrary address and get the > performance hit. > > I think the default should remain as is and the ability to map the kernel > with 4K pages (and use 4K aligned load address) should be a Kconfig option.
Agreed. That Kconfig parameter should also be default-off. Only a small number of people will try to run RISC-V Linux on a Kendryte board. That niche use-case shouldn't impact the much larger group of people who will run Linux on more reasonably-sized systems. No one should need to ask people to report their kernel load address whenever someone reports a performance regression. - Paul
