Re: [PATCH v6 4/6] mm: change folio_lock_or_retry to use vm_fault directly

[Matthew Wilcox]

On Thu, Jun 29, 2023 at 07:04:33PM -0700, Suren Baghdasaryan wrote:
> Change folio_lock_or_retry to accept vm_fault struct and return the
> vm_fault_t directly.

I thought we decided to call this folio_lock_fault()?

> +static inline vm_fault_t folio_lock_or_retry(struct folio *folio,
> +					     struct vm_fault *vmf)
>  {
>  	might_sleep();
> -	return folio_trylock(folio) || __folio_lock_or_retry(folio, mm, flags);
> +	return folio_trylock(folio) ? 0 : __folio_lock_or_retry(folio, vmf);

No, don't use the awful ternary operator.  The || form is used
everywhere else.

>  /*
>   * Return values:
> - * true - folio is locked; mmap_lock is still held.
> - * false - folio is not locked.
> + * 0 - folio is locked.
> + * VM_FAULT_RETRY - folio is not locked.

I don't think we want to be so prescriptive here.  It returns non-zero
if the folio is not locked.  The precise value is not something that
callers should depend on.