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

[Suren Baghdasaryan]

On Thu, Jun 29, 2023 at 8:36 PM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote:
>
> 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.

Ok, but folio_trylock() returns a boolean while folio_lock_or_retry
should return vm_fault_t. How exactly do you suggest changing this?
Something like this perhaps:

static inline vm_fault_t folio_lock_or_retry(struct folio *folio,
                                          struct vm_fault *vmf)
{
     might_sleep();
     if (folio_trylock(folio))
         return 0;
     return __folio_lock_or_retry(folio, mm, flags);
}

?


>
> >  /*
> >   * 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.

Ok, I'll change it to "non-zero" here.

>