On Wed, Sep 25, 2024 at 7:21 AM Nhat Pham <nphamcs@xxxxxxxxx> wrote:
>
>
> I'm only supporting the case nr > 1, when there is no need to add swap
> continuations :) That's the only current use case right now (shmem) :)
Sorry, I forgot to say - but to fully support a batched variant, we
can do something like this:
>
> 1. Keep the non-batched variant:
>
> int swap_duplicate(swp_entry_t entry)
> {
> int err = 0;
>
> while (!err && __swap_duplicate(entry, 1, 1) == -ENOMEM)
> err = add_swap_count_continuation(entry, GFP_ATOMIC);
> return err;
> }
>
> 2. Implement the batched variant:
>
> int swap_duplicate_nr(swp_entry_t entry, int nr)
> {
> swp_entry_t cur_entry;
> int i, err;
>
> if (nr == 1)
> return swap_duplicate(entry);
>
> err = __swap_duplicate(entry, 1, nr);
> if (err == -ENOMEM) {
> /* fallback to non-batched version */
> for (i = 0; i < nr; i++) {
> cur_entry = (swp_entry_t){entry.val + i};
> if (swap_duplicate(cur_entry)) {
> /* rollback */
> while (--i >= 0) {
> cur_entry = (swp_entry_t){entry.val + i};
> swap_free(cur_entry);
> }
missing a "return err;" here. Not my best idea to write (pseudo) code
before caffeine in the morning :)
> }
> }
> }
> return err;
> }
>
> How does this look? My concern is that there is not really a use for
> the fallback logic. Basically dead code.
>
> I can keep it in if you guys have a use for it soon, but otherwise I
> lean towards just adding a WARN etc. there, or return -ENOMEM, and
> WARN at shmem's callsite (because it cannot get -ENOMEM).
