On Mon, Feb 18, 2019 at 03:12:23PM +0000, Will Deacon wrote: > [+Mark] > > On Thu, Feb 14, 2019 at 02:16:42PM -0700, Yu Zhao wrote: > > Switch from per mm_struct to per pmd page table lock by enabling > > ARCH_ENABLE_SPLIT_PMD_PTLOCK. This provides better granularity for > > large system. > > > > I'm not sure if there is contention on mm->page_table_lock. Given > > the option comes at no cost (apart from initializing more spin > > locks), why not enable it now. > > > > Signed-off-by: Yu Zhao <[email protected]> > > --- > > arch/arm64/Kconfig | 3 +++ > > arch/arm64/include/asm/pgalloc.h | 12 +++++++++++- > > arch/arm64/include/asm/tlb.h | 5 ++++- > > 3 files changed, 18 insertions(+), 2 deletions(-) > > > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > > index a4168d366127..104325a1ffc3 100644 > > --- a/arch/arm64/Kconfig > > +++ b/arch/arm64/Kconfig > > @@ -872,6 +872,9 @@ config ARCH_WANT_HUGE_PMD_SHARE > > config ARCH_HAS_CACHE_LINE_SIZE > > def_bool y > > > > +config ARCH_ENABLE_SPLIT_PMD_PTLOCK > > + def_bool y > > + > > config SECCOMP > > bool "Enable seccomp to safely compute untrusted bytecode" > > ---help--- > > diff --git a/arch/arm64/include/asm/pgalloc.h > > b/arch/arm64/include/asm/pgalloc.h > > index 52fa47c73bf0..dabba4b2c61f 100644 > > --- a/arch/arm64/include/asm/pgalloc.h > > +++ b/arch/arm64/include/asm/pgalloc.h > > @@ -33,12 +33,22 @@ > > > > static inline pmd_t *pmd_alloc_one(struct mm_struct *mm, unsigned long > > addr) > > { > > - return (pmd_t *)__get_free_page(PGALLOC_GFP); > > + struct page *page; > > + > > + page = alloc_page(PGALLOC_GFP); > > + if (!page) > > + return NULL; > > + if (!pgtable_pmd_page_ctor(page)) { > > + __free_page(page); > > + return NULL; > > + } > > + return page_address(page); > > I'm a bit worried as to how this interacts with the page-table code in > arch/arm64/mm/mmu.c when pgd_pgtable_alloc is used as the allocator. It > looks like that currently always calls pgtable_page_ctor(), regardless of > level. Do we now need a separate allocator function for the PMD level?
Thanks for reminding me, I never noticed this. The short answer is no. I guess pgtable_page_ctor() is used on all pud/pmd/pte entries there because it's also compatible with pud, and pmd too without this patch. So your concern is valid. Thanks again. Why my answer is no? Because I don't think the ctor matters for pgd_pgtable_alloc(). The ctor is only required for userspace page tables, and that's why we don't have it in pte_alloc_one_kernel(). AFAICT, none of the pgds (efi_mm.pgd, tramp_pg_dir and init_mm.pgd) pre-populated by pgd_pgtable_alloc() is. (I doubt we pre-populate userspace page tables in any other arch). So to avoid future confusion, we might just remove the ctor from pgd_pgtable_alloc().
