From mboxrd@z Thu Jan 1 00:00:00 1970 From: Daniel Axtens Date: Fri, 20 Aug 2021 00:03:08 +0000 Subject: Re: [PATCH v2 2/2] powerpc: rectify selection to ARCH_ENABLE_SPLIT_PMD_PTLOCK Message-Id: <87pmu99e4j.fsf@dja-thinkpad.axtens.net> List-Id: References: <20210819113954.17515-1-lukas.bulwahn@gmail.com> <20210819113954.17515-3-lukas.bulwahn@gmail.com> In-Reply-To: <20210819113954.17515-3-lukas.bulwahn@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Lukas Bulwahn , Paul Mackerras , Michael Ellerman , Benjamin Herrenschmidt , Michael Neuling , Anshuman Khandual , kvm-ppc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org Cc: Lukas Bulwahn , kernel-janitors@vger.kernel.org, stable@vger.kernel.org, linux-kernel@vger.kernel.org Lukas Bulwahn 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 Kind regards, Daniel > Fixes: 66f24fa766e3 ("mm: drop redundant ARCH_ENABLE_SPLIT_PMD_PTLOCK") > Signed-off-by: Lukas Bulwahn > --- > 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