Re: [PATCH v2 1/1] swap: shmem: remove SWAP_MAP_SHMEM

[Yosry Ahmed <yosryahmed@google.com>]

[..]
> > > + *
> > > + * @entry: first swap entry from which we want to increase the refcount.
> > > + * @nr: Number of entries in range.
> > > + *
> > >   * Returns 0 for success, or -ENOMEM if a swap_count_continuation is required
> > >   * but could not be atomically allocated.  Returns 0, just as if it succeeded,
> > >   * if __swap_duplicate() fails for another reason (-EINVAL or -ENOENT), which
> > >   * might occur if a page table entry has got corrupted.
> > > + *
> > > + * Note that we are currently not handling the case where nr > 1 and we need to
> > > + * add swap count continuation. This is OK, because no such user exists - shmem
> > > + * is the only user that can pass nr > 1, and it never re-duplicates any swap
> > > + * entry it owns.
> >
> > Do we need this comment when we have the WARN + comment in __swap_duplicate()?
>
> Here I'm just being cautious and include the limitation of the
> function in the API documentation itself.
>
> No strong opinions though.

Maybe it would be more useful to add a warning in the loop if nr > 1,
with a comment that explains that the current -ENOMEM handling does
not properly handle nr > 1?

> >
> > >   */
> > > -int swap_duplicate(swp_entry_t entry)
> > > +int swap_duplicate_nr(swp_entry_t entry, int nr)
> > >  {
> > >         int err = 0;
> > >
> > > -       while (!err && __swap_duplicate(entry, 1, 1) == -ENOMEM)
> > > +       while (!err && __swap_duplicate(entry, 1, nr) == -ENOMEM)
> > >                 err = add_swap_count_continuation(entry, GFP_ATOMIC);
> > >         return err;
> > >  }
> > > --
> > > 2.43.5