Messages in this thread | | | From | Suren Baghdasaryan <> | Date | Tue, 23 May 2023 22:28:29 -0700 | Subject | Re: [PATCH] riscv: mm: try VMA lock-based page fault handling first |
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On Tue, May 23, 2023 at 10:03 PM <guoren@kernel.org> wrote: > > > Attempt VMA lock-based page fault handling first, and fall back to the > > existing mmap_lock-based handling if that fails. > > > > A simple running the ebizzy benchmark on Lichee Pi 4A shows that > > PER_VMA_LOCK can improve the ebizzy benchmark by about 32.68%. In > Good improvement, I think VMA lock is worth to support in riscv. > > Please give more details about ebizzy, Is it > https://github.com/linux-test-project/ltp/blob/master/utils/benchmark/ebizzy-0.3/ebizzy.c > ? > > > theory, the more CPUs, the bigger improvement, but I don't have any > > HW platform which has more than 4 CPUs. > > > > This is the riscv variant of "x86/mm: try VMA lock-based page fault > > handling first". > > > > How about add Link tag here: > Link: https://lwn.net/Articles/906852/ > > > Signed-off-by: Jisheng Zhang <jszhang@kernel.org> > > --- > > Any performance numbers are welcome! Especially the numbers on HW > > platforms with 8 or more CPUs. > > > > arch/riscv/Kconfig | 1 + > > arch/riscv/mm/fault.c | 33 +++++++++++++++++++++++++++++++++ > > 2 files changed, 34 insertions(+) > > > > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig > > index 62e84fee2cfd..b958f67f9a12 100644 > > --- a/arch/riscv/Kconfig > > +++ b/arch/riscv/Kconfig > > @@ -42,6 +42,7 @@ config RISCV > > select ARCH_SUPPORTS_DEBUG_PAGEALLOC if MMU > > select ARCH_SUPPORTS_HUGETLBFS if MMU > > select ARCH_SUPPORTS_PAGE_TABLE_CHECK if MMU > > + select ARCH_SUPPORTS_PER_VMA_LOCK if MMU > > select ARCH_USE_MEMTEST > > select ARCH_USE_QUEUED_RWLOCKS > > select ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT if MMU > > diff --git a/arch/riscv/mm/fault.c b/arch/riscv/mm/fault.c > > index 8685f85a7474..eccdddf26f4b 100644 > > --- a/arch/riscv/mm/fault.c > > +++ b/arch/riscv/mm/fault.c > > @@ -286,6 +286,36 @@ void handle_page_fault(struct pt_regs *regs) > > flags |= FAULT_FLAG_WRITE; > > else if (cause == EXC_INST_PAGE_FAULT) > > flags |= FAULT_FLAG_INSTRUCTION; > > +#ifdef CONFIG_PER_VMA_LOCK > > + if (!(flags & FAULT_FLAG_USER)) > > + goto lock_mmap; > > + > > + vma = lock_vma_under_rcu(mm, addr); > > + if (!vma) > > + goto lock_mmap; > > + > > + if (unlikely(access_error(cause, vma))) { > > + vma_end_read(vma); > > + goto lock_mmap; > > + } > > + > > + fault = handle_mm_fault(vma, addr, flags | FAULT_FLAG_VMA_LOCK, regs); > > + vma_end_read(vma); > > + > > + if (!(fault & VM_FAULT_RETRY)) { > > + count_vm_vma_lock_event(VMA_LOCK_SUCCESS); > > + goto done; > > + } > > + count_vm_vma_lock_event(VMA_LOCK_RETRY); > > + > > + if (fault_signal_pending(fault, regs)) { > > + if (!user_mode(regs)) > > + no_context(regs, addr); > > + return; > > + } > > +lock_mmap: > > +#endif /* CONFIG_PER_VMA_LOCK */ > > + > > retry: > > mmap_read_lock(mm); > > vma = find_vma(mm, addr); > > @@ -355,6 +385,9 @@ void handle_page_fault(struct pt_regs *regs) > > > > mmap_read_unlock(mm); > > > > +#ifdef CONFIG_PER_VMA_LOCK > > +done: > > +#endif > It's very close to cd7f176aea5f ("arm64/mm: try VMA lock-based page fault > handling first"), and I didn't find any problem. So: > > Reviewed-by: Guo Ren <guoren@kernel.org>
Looks correct to me.
Reviewed-by: Suren Baghdasaryan <surenb@google.com>
> > F.Y.I Huacai Chen, maybe he also would be interesting this new feature. > > > > if (unlikely(fault & VM_FAULT_ERROR)) { > > tsk->thread.bad_cause = cause; > > mm_fault_error(regs, addr, fault); > > -- > > 2.40.1
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