Messages in this thread | | | From | guoren@kernel ... | Subject | Re: [PATCH] riscv: mm: try VMA lock-based page fault handling first | Date | Wed, 24 May 2023 01:02:59 -0400 |
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> 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>
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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