Lukas Bulwahn lukas.bulwahn@gmail.com writes:
Commit 66f24fa766e3 ("mm: drop redundant ARCH_ENABLE_SPLIT_PMD_PTLOCK") selects the non-existing config ARCH_ENABLE_PMD_SPLIT_PTLOCK in ./arch/powerpc/platforms/Kconfig.cputype, but clearly it intends to select ARCH_ENABLE_SPLIT_PMD_PTLOCK here (notice the word swapping!), as this commit does select that for all other architectures.
Rectify selection to ARCH_ENABLE_SPLIT_PMD_PTLOCK instead.
Yikes, yes, 66f24fa766e3 does seem to have got that wrong. It looks like that went into 5.13.
I think we want to specifically target this for stable so that we don't lose the perfomance and scalability benefits of split pmd ptlocks:
Cc: stable@vger.kernel.org # v5.13+
(I don't think you need to do another revision for this, I think mpe could add it when merging.)
I tried to check whether we accidentally broke SPLIT_PMD_PTLOCKs while they were disabled:
- There hasn't been any change to the pgtable_pmd_page_ctor or _dtor prototypes, and we haven't made any relevant changes to any of the files in arch/powerpc that called it.
- I checked out v5.13 and powerpc/merge, applied this patch, built a pseries_le_defconfig and boot tested it in qemu. It didn't crash on boot or with /bin/sh and some shell commands, but I didn't exactly stress test the VM subsystem either.
This gives me some confidence it's both good for powerpc and stable-worthy.
Overall: Reviewed-by: Daniel Axtens dja@axtens.net
Kind regards, Daniel
Fixes: 66f24fa766e3 ("mm: drop redundant ARCH_ENABLE_SPLIT_PMD_PTLOCK") Signed-off-by: Lukas Bulwahn lukas.bulwahn@gmail.com
arch/powerpc/platforms/Kconfig.cputype | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/powerpc/platforms/Kconfig.cputype b/arch/powerpc/platforms/Kconfig.cputype index 6794145603de..a208997ade88 100644 --- a/arch/powerpc/platforms/Kconfig.cputype +++ b/arch/powerpc/platforms/Kconfig.cputype @@ -98,7 +98,7 @@ config PPC_BOOK3S_64 select PPC_HAVE_PMU_SUPPORT select HAVE_ARCH_TRANSPARENT_HUGEPAGE select ARCH_ENABLE_HUGEPAGE_MIGRATION if HUGETLB_PAGE && MIGRATION
- select ARCH_ENABLE_PMD_SPLIT_PTLOCK
- select ARCH_ENABLE_SPLIT_PMD_PTLOCK select ARCH_ENABLE_THP_MIGRATION if TRANSPARENT_HUGEPAGE select ARCH_SUPPORTS_HUGETLBFS select ARCH_SUPPORTS_NUMA_BALANCING
-- 2.26.2