Re: [PATCH v2 6/9] mm: Move the FAULT_FLAG_VMA_LOCK check down from do_fault()

[Suren Baghdasaryan <surenb@google.com>]

On Tue, Jul 11, 2023 at 1:21 PM Matthew Wilcox (Oracle)
<willy@infradead.org> wrote:
>
> Perform the check at the start of do_read_fault(), do_cow_fault()
> and do_shared_fault() instead.  Should be no performance change from
> the last commit.
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>

Reviewed-by: Suren Baghdasaryan <surenb@google.com>

> ---
>  mm/memory.c | 20 +++++++++++++++-----
>  1 file changed, 15 insertions(+), 5 deletions(-)
>
> diff --git a/mm/memory.c b/mm/memory.c
> index 88cf9860f17e..709bffee8aa2 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -4547,6 +4547,11 @@ static vm_fault_t do_read_fault(struct vm_fault *vmf)
>         vm_fault_t ret = 0;
>         struct folio *folio;
>
> +       if (vmf->flags & FAULT_FLAG_VMA_LOCK) {
> +               vma_end_read(vmf->vma);
> +               return VM_FAULT_RETRY;
> +       }
> +
>         /*
>          * Let's call ->map_pages() first and use ->fault() as fallback
>          * if page by the offset is not ready to be mapped (cold cache or
> @@ -4575,6 +4580,11 @@ static vm_fault_t do_cow_fault(struct vm_fault *vmf)
>         struct vm_area_struct *vma = vmf->vma;
>         vm_fault_t ret;
>
> +       if (vmf->flags & FAULT_FLAG_VMA_LOCK) {
> +               vma_end_read(vma);
> +               return VM_FAULT_RETRY;
> +       }
> +
>         if (unlikely(anon_vma_prepare(vma)))
>                 return VM_FAULT_OOM;
>
> @@ -4615,6 +4625,11 @@ static vm_fault_t do_shared_fault(struct vm_fault *vmf)
>         vm_fault_t ret, tmp;
>         struct folio *folio;
>
> +       if (vmf->flags & FAULT_FLAG_VMA_LOCK) {
> +               vma_end_read(vma);
> +               return VM_FAULT_RETRY;
> +       }
> +
>         ret = __do_fault(vmf);
>         if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY)))
>                 return ret;
> @@ -4661,11 +4676,6 @@ static vm_fault_t do_fault(struct vm_fault *vmf)
>         struct mm_struct *vm_mm = vma->vm_mm;
>         vm_fault_t ret;
>
> -       if (vmf->flags & FAULT_FLAG_VMA_LOCK){
> -               vma_end_read(vma);
> -               return VM_FAULT_RETRY;
> -       }
> -
>         /*
>          * The VMA was not fully populated on mmap() or missing VM_DONTEXPAND
>          */
> --
> 2.39.2
>