Re: [PATCH v2 1/1] mm: do not increment pgfault stats when page fault handler retries

Matthew Wilcox
2023-04-17T17:27:10Z

On Fri, Apr 14, 2023 at 05:08:18PM -0700, Suren Baghdasaryan wrote:
> /*
> - * We don't do accounting for some specific faults:
> - *
> - * - Unsuccessful faults (e.g. when the address wasn't valid). That
> - * includes arch_vma_access_permitted() failing before reaching here.
> - * So this is not a "this many hardware page faults" counter. We
> - * should use the hw profiling for that.
> - *
> - * - Incomplete faults (VM_FAULT_RETRY). They will only be counted
> - * once they're completed.
> + * Do not account for incomplete faults (VM_FAULT_RETRY). They will be

I don't think you need the "(VM_FAULT_RETRY)" here.

> @@ -5180,21 +5186,22 @@ static vm_fault_t sanitize_fault_flags(struct vm_area_struct *vma,
> vm_fault_t handle_mm_fault(struct vm_area_struct *vma, unsigned long address,
> unsigned int flags, struct pt_regs *regs)
> {
> + /* Copy vma->vm_mm in case mmap_lock is dropped and vma becomes unstable. */

How about:

/* If the fault handler drops the mmap_lock, vma may be freed */

> + struct mm_struct *mm = vma->vm_mm;