Make 64K pages the default in Kconfig for Book3S/64

[mpe]

Currently we have:

choice
	prompt "Page size"
	default PPC_4K_PAGES

For 64-bit BOOK3S the default should really be 64K, that's what modern CPUs are designed for.

It should be just a matter of:

	default PPC_64K_PAGES if PPC_BOOK3S_64

And then we need to update the defconfigs to account for the flip.

[grooverdan]

fyi I've seen userspace/libraries (e.g. jemalloc) processes that (incorrectly) assume 64k page size on ppc64 and will crash on a 4K kernel setting.

[shenki]

Find the 64s machines

PPC_BOOK3S_64 is the default for PPC64, so we need to find machines that are PPC64 and set PPC_BOOK3E_64.

$ git grep -l PPC64=y arch/powerpc/configs/ 
arch/powerpc/configs/64-bit.config
arch/powerpc/configs/85xx-64bit.config
arch/powerpc/configs/cell_defconfig
arch/powerpc/configs/g5_defconfig
arch/powerpc/configs/maple_defconfig
arch/powerpc/configs/microwatt_defconfig
arch/powerpc/configs/pasemi_defconfig
arch/powerpc/configs/powernv_defconfig
arch/powerpc/configs/ppc64_defconfig
arch/powerpc/configs/ppc64e_defconfig
arch/powerpc/configs/ppc64le.config
arch/powerpc/configs/ps3_defconfig
arch/powerpc/configs/pseries_defconfig
arch/powerpc/configs/skiroot_defconfig
joel@voyager ~/dev/kernels/linux-next :(801a837d7533...) 
$ git grep -l PPC64=y arch/powerpc/configs/ | xargs git grep -l PPC_BOOK3E_64=y
arch/powerpc/configs/85xx-64bit.config
arch/powerpc/configs/ppc64e_defconfig

Configs we are interested in

arch/powerpc/configs/64-bit.config
arch/powerpc/configs/cell_defconfig
arch/powerpc/configs/g5_defconfig
arch/powerpc/configs/maple_defconfig
arch/powerpc/configs/microwatt_defconfig
arch/powerpc/configs/pasemi_defconfig
arch/powerpc/configs/powernv_defconfig
arch/powerpc/configs/ppc64_defconfig
arch/powerpc/configs/ppc64le.config
arch/powerpc/configs/ps3_defconfig
arch/powerpc/configs/pseries_defconfig
arch/powerpc/configs/skiroot_defconfig

64-bit.config and ppc64le used to seed dynamically generated configs so they can be ignored.

$ cat configs.txt
cell
g5
maple
microwatt
pasemi
powernv
ppc64
ps3
pseries
skiroot

Generate .configs from existing defconfigs

for config in `cat configs.txt`; do ARCH=powerpc make O=$config ${config}_defconfig; done

Apply the change

git am 0001-powerpc-Make-64K-pages-the-default-for-Book3S.patch

Generate new configs

for config in `cat configs.txt`; do ARCH=powerpc make O=${config}_64k ${config}_defconfig; done

Show differences

for config in `cat configs.txt`; do diff -upqs ${config}/.config ${config}_64k/.config; done 

Files cell/.config and cell_64k/.config are identical
Files g5/.config and g5_64k/.config differ
Files maple/.config and maple_64k/.config differ
Files microwatt/.config and microwatt_64k/.config differ
Files pasemi/.config and pasemi_64k/.config are identical
Files powernv/.config and powernv_64k/.config are identical
Files ppc64/.config and ppc64_64k/.config are identical
Files ps3/.config and ps3_64k/.config differ
Files pseries/.config and pseries_64k/.config are identical
Files skiroot/.config and skiroot_64k/.config are identical

Add 4K to the configs that are identical

This can be done by doing a savedefconfig on the old configuration, which has CONFIG_PPC_4K_PAGES=y.

In hindsight that would have been an easier method: create the .configs using the defconfigs, modify the default in Kconfig, and savedefconfig all of the old config files.

The downside of this approach is the noise from regenerating the defconfigs, so perhaps do that first.

[shenki]

https://lore.kernel.org/all/20211013233133.728484-1-joel@jms.id.au/

[shenki]

https://lore.kernel.org/r/20211015001649.45591-1-joel@jms.id.au

Merged in v5.16-rc1 torvalds/linux@f22969a