[v2,2/7] arm64: mm: accelerate pagefault when VM_FAULT_BADACCESS

Commit Message

Kefeng Wang April 3, 2024, 8:38 a.m. UTC

The vm_flags of vma already checked under per-VMA lock, if it is a
bad access, directly set fault to VM_FAULT_BADACCESS and handle error,
no need to retry with mmap_lock again, the latency time reduces 34% in
'lat_sig -P 1 prot lat_sig' from lmbench testcase.

Since the page faut is handled under per-VMA lock, count it as a vma lock
event with VMA_LOCK_SUCCESS.

Reviewed-by: Suren Baghdasaryan <[e-mail]>
Signed-off-by: Kefeng Wang <[e-mail]>
---
 arch/arm64/mm/fault.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

Comments

Catalin Marinas April 9, 2024, 11:15 a.m. UTC | #1

On Wed, Apr 03, 2024 at 04:38:00PM +0800, Kefeng Wang wrote:
> The vm_flags of vma already checked under per-VMA lock, if it is a
> bad access, directly set fault to VM_FAULT_BADACCESS and handle error,
> no need to retry with mmap_lock again, the latency time reduces 34% in
> 'lat_sig -P 1 prot lat_sig' from lmbench testcase.
> 
> Since the page faut is handled under per-VMA lock, count it as a vma lock
> event with VMA_LOCK_SUCCESS.
> 
> Reviewed-by: Suren Baghdasaryan <[e-mail]>
> Signed-off-by: Kefeng Wang <[e-mail]>

Reviewed-by: Catalin Marinas <[e-mail]>

Patch

diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index 9bb9f395351a..405f9aa831bd 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -572,7 +572,9 @@  static int __kprobes do_page_fault(unsigned long far, unsigned long esr,
 
 	if (!(vma->vm_flags & vm_flags)) {
 		vma_end_read(vma);
-		goto lock_mmap;
+		fault = VM_FAULT_BADACCESS;
+		count_vm_vma_lock_event(VMA_LOCK_SUCCESS);
+		goto done;
 	}
 	fault = handle_mm_fault(vma, addr, mm_flags | FAULT_FLAG_VMA_LOCK, regs);
 	if (!(fault & (VM_FAULT_RETRY | VM_FAULT_COMPLETED)))