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

[Suren Baghdasaryan]

On Thu, Jun 29, 2023 at 8:47 PM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote:
>
> On Thu, Jun 29, 2023 at 08:45:39PM -0700, Suren Baghdasaryan wrote:
> > 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);
> > }
> >
> > ?
>
> I think the automatic casting would work, but I prefer what you've
> written here.
>
> > > >  /*
> > > >   * 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.
>
> Thanks!

Posted v7 at https://lore.kernel.org/all/20230630211957.1341547-1-surenb@xxxxxxxxxx/