Re: [PATCH 1/3] mm: handle swap page faults under VMA lock if page is uncontended

[Matthew Wilcox]

On Mon, May 01, 2023 at 10:50:23AM -0700, Suren Baghdasaryan wrote:
> +++ b/mm/memory.c
> @@ -3711,11 +3711,6 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
>  	if (!pte_unmap_same(vmf))
>  		goto out;
>  
> -	if (vmf->flags & FAULT_FLAG_VMA_LOCK) {
> -		ret = VM_FAULT_RETRY;
> -		goto out;
> -	}
> -
>  	entry = pte_to_swp_entry(vmf->orig_pte);
>  	if (unlikely(non_swap_entry(entry))) {
>  		if (is_migration_entry(entry)) {

You're missing the necessary fallback in the (!folio) case.
swap_readpage() is synchronous and will sleep.