Does HIGHMEM work on 32-bit MIPS ports?
As we continue to investigate using high memory on MIPS, we keep coming up with odd results. The basic mapping of high memory seems to be working correctly, and if we use an INITRAMFS root filesystem, things seem to work. Things also seem to work with an NFS root filesystem if we disable preemption, though we get someone squirrelly behavior in some minor ways. Has anyone else successfully been able to use high memory on a 32-bit MIPS Linux port?
Any feedback would be helpful.
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David VomLehn, [email protected] The opinions expressed herein are likely mine, but might not be my employer's...
Quoted 7 lines · David VomLehn
As we continue to investigate using high memory on MIPS, we keep coming up with odd results. The basic mapping of high memory seems to be working correctly, and if we use an INITRAMFS root filesystem, things seem to work. Things also seem to work with an NFS root filesystem if we disable preemption, though we get someone squirrelly behavior in some minor ways. Has anyone else successfully been able to use high memory on a 32-bit MIPS Linux port?
I've written MIPS highmem support in late 2002 for a customer who back then wasn't interested in being the first through the 64-bit minefield. Which back then certainly was justified - but there are now fairly stable 64-bit Linux kernels available so if you happen to be running on 64-bit hardware don't even spend a nanosecond on thinking about 32-bit highmem kernels. Highmem fundamentally sucks rocks through a straw.
Coming back to your question. Highmem was only ever tested to work on SB1 and somewhat later PMC-Sierra RM9000 cores, both being 64-bit. With the increasing maturity of 64-bit Linux interest in these went away and as the result the highmem code started a slow bitrot - unnoticed for many moons.
Ralf