On Mon, Sep 16, 2013 at 01:42:05PM +0300, Kirill A. Shutemov wrote: > Naoya Horiguchi wrote: > > Hi, > > > > Kirill posted split_ptl patchset for thp today, so in this version > > I post only hugetlbfs part. I added Kconfig variables in following > > Kirill's patches (although without CONFIG_SPLIT_*_PTLOCK_CPUS.) > > > > This patch changes many lines, but all are in hugetlbfs specific code, > > so I think we can apply this independent of thp patches. > > ----- > > From: Naoya Horiguchi <[email protected]> > > Date: Fri, 13 Sep 2013 18:12:30 -0400 > > Subject: [PATCH v4] hugetlbfs: support split page table lock > > > > Currently all of page table handling by hugetlbfs code are done under > > mm->page_table_lock. So when a process have many threads and they heavily > > access to the memory, lock contention happens and impacts the performance. > > > > This patch makes hugepage support split page table lock so that we use > > page->ptl of the leaf node of page table tree which is pte for normal pages > > but can be pmd and/or pud for hugepages of some architectures. > > > > ChangeLog v4: > > - introduce arch dependent macro ARCH_ENABLE_SPLIT_HUGETLB_PTLOCK > > (only defined for x86 for now) > > - rename USE_SPLIT_PTLOCKS_HUGETLB to USE_SPLIT_HUGETLB_PTLOCKS > > > > ChangeLog v3: > > - disable split ptl for ppc with USE_SPLIT_PTLOCKS_HUGETLB. > > - remove replacement in some architecture dependent code. This is justified > > because an allocation of pgd/pud/pmd/pte entry can race with other > > allocation, not with read/write access, so we can use different locks. > > http://thread.gmane.org/gmane.linux.kernel.mm/106292/focus=106458 > > > > ChangeLog v2: > > - add split ptl on other archs missed in v1 > > - drop changes on arch/{powerpc,tile}/mm/hugetlbpage.c > > > > Signed-off-by: Naoya Horiguchi <[email protected]> > > --- > > arch/x86/Kconfig | 4 +++ > > include/linux/hugetlb.h | 20 +++++++++++ > > include/linux/mm_types.h | 2 ++ > > mm/Kconfig | 3 ++ > > mm/hugetlb.c | 92 > > +++++++++++++++++++++++++++++------------------- > > mm/mempolicy.c | 5 +-- > > mm/migrate.c | 4 +-- > > mm/rmap.c | 2 +- > > 8 files changed, 91 insertions(+), 41 deletions(-) > > > > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig > > index 6a5cf6a..5b83d14 100644 > > --- a/arch/x86/Kconfig > > +++ b/arch/x86/Kconfig > > @@ -1884,6 +1884,10 @@ config ARCH_ENABLE_SPLIT_PMD_PTLOCK > > def_bool y > > depends on X86_64 || X86_PAE > > > > +config ARCH_ENABLE_SPLIT_HUGETLB_PTLOCK > > + def_bool y > > + depends on X86_64 || X86_PAE > > + > > menu "Power management and ACPI options" > > > > config ARCH_HIBERNATION_HEADER > > diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h > > index 0393270..2cdac68 100644 > > --- a/include/linux/hugetlb.h > > +++ b/include/linux/hugetlb.h > > @@ -80,6 +80,24 @@ extern const unsigned long hugetlb_zero, > > hugetlb_infinity; > > extern int sysctl_hugetlb_shm_group; > > extern struct list_head huge_boot_pages; > > > > +#if USE_SPLIT_HUGETLB_PTLOCKS > > +#define huge_pte_lockptr(mm, ptep) ({__pte_lockptr(virt_to_page(ptep)); }) > > +#else /* !USE_SPLIT_HUGETLB_PTLOCKS */ > > +#define huge_pte_lockptr(mm, ptep) ({&(mm)->page_table_lock; }) > > +#endif /* USE_SPLIT_HUGETLB_PTLOCKS */ > > + > > +#define huge_pte_offset_lock(mm, address, ptlp) \ > > +({ \ > > + pte_t *__pte = huge_pte_offset(mm, address); \ > > + spinlock_t *__ptl = NULL; \ > > + if (__pte) { \ > > + __ptl = huge_pte_lockptr(mm, __pte); \ > > + *(ptlp) = __ptl; \ > > + spin_lock(__ptl); \ > > + } \ > > + __pte; \ > > +}) > > + > > [ Disclaimer: I don't know much about hugetlb. ] > > I don't think it's correct. Few points: > > - Hugetlb supports multiple page sizes: on x86_64 2M (PMD) and 1G (PUD). > My patchset only implements it for PMD. We don't even initialize > spinlock in struct page for PUD.
In hugetlbfs code, we use huge_pte_offset() to get leaf level entries which can be pud or pmd in x86. huge_pte_lockptr() uses this function, so we can always get the correct ptl regardless of hugepage sizes. As for spinlock initialization, you're right. I'll add it on huge_pte_alloc(). > - If we enable split PMD lock we should use it *globally*. With you patch > we can end up with different locks used by hugetlb and rest of kernel > to protect the same PMD table if USE_SPLIT_HUGETLB_PTLOCKS != > USE_SPLIT_PMD_PTLOCKS. It's just broken. I don't think so. Thp specific operations (like thp allocation, split, and collapse) are never called on the virtual address range covered by vma(VM_HUGETLB) by checking VM_HUGETLB. So no one tries to lock/unlock a ptl concurrently from thp context and hugetlbfs context. > What we should really do is take split pmd lock (using pmd_lock*) if we > try to protect PMD level and fallback to mm->page_table_lock if we want to > protect upper levels. > > > /* arch callbacks */ > > > > pte_t *huge_pte_alloc(struct mm_struct *mm, > > @@ -164,6 +182,8 @@ static inline void __unmap_hugepage_range(struct > > mmu_gather *tlb, > > BUG(); > > } > > > > +#define huge_pte_lockptr(mm, ptep) 0 > > + > > NULL? OK. Thanks, Naoya Horiguchi > > #endif /* !CONFIG_HUGETLB_PAGE */ > > > > #define HUGETLB_ANON_FILE "anon_hugepage" > > -- > Kirill A. Shutemov > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
