Ben Hutchings <b...@decadent.org.uk> writes: > On Mon, 2019-03-25 at 01:03 +0100, Andreas Schwab wrote: >> On Mär 24 2019, Ben Hutchings <b...@decadent.org.uk> wrote: >> >> > Presumably you have CONFIG_PPC_BOOK3S_64 enabled and >> > CONFIG_SPARSEMEM >> > disabled? Was this configuration actually usable? >> >> Why not? > > I assume that CONFIG_SPARSEMEM is the default for a good reason. > What I don't know is how strong that reason is (I am not a Power expert > at all). Looking a bit further, it seems to be related to CONFIG_NUMA > in that you can enable CONFIG_FLATMEM if and only if that's disabled. > So I suppose the configuration you used works for non-NUMA systems.
Aneesh pointed out this fix would break FLATMEM after I'd merged it, but it didn't break any of our defconfigs so I wondered if anyone would notice. I checked today and a G5 will boot with FLATMEM, which I assume is what Andreas is using. I guess we should fix this build break for now. Even some G5's have discontiguous memory, so FLATMEM is not clearly a good choice even for all G5's, and actually a fresh g5_defconfig uses SPARSEMEM. So I'm inclined to just switch to always using SPARSEMEM on 64-bit Book3S, because that's what's well tested and we hardly need more code paths to test. Unless anyone has a strong objection, I haven't actually benchmarked FLATMEM vs SPARSEMEM on a G5. cheers