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

[Catalin Marinas]

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 
> Signed-off-by: Kefeng Wang 

Reviewed-by: Catalin Marinas 

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

[Kefeng Wang]

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 
Signed-off-by: Kefeng Wang 
---
 arch/arm64/mm/fault.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

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)))
-- 
2.27.0