On Tue, Jul 11, 2023 at 1:20 PM Matthew Wilcox (Oracle)
<willy@xxxxxxxxxxxxx> wrote:
>
> The map_pages fs method should be safe to run under the VMA lock instead
> of the mmap lock. This should have a measurable reduction in contention
> on the mmap lock.
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
I'll trust your claim that vmf->vma->vm_ops->map_pages() never rely on
mmap_lock. I think it makes sense but I did not check every case :)
Reviewed-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
> ---
> mm/memory.c | 10 +++++-----
> 1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/mm/memory.c b/mm/memory.c
> index 709bffee8aa2..0a4e363b0605 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -4547,11 +4547,6 @@ 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
> @@ -4563,6 +4558,11 @@ static vm_fault_t do_read_fault(struct vm_fault *vmf)
> return ret;
> }
>
> + if (vmf->flags & FAULT_FLAG_VMA_LOCK) {
> + vma_end_read(vmf->vma);
> + return VM_FAULT_RETRY;
> + }
> +
> ret = __do_fault(vmf);
> if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY)))
> return ret;
> --
> 2.39.2
>
