Re: [RFC PATCH 0/2] remove SWAP_MAP_SHMEM

[Huang, Ying]

Nhat Pham <nphamcs@xxxxxxxxx> writes:

[snip]

>
> My understanding now is that there are two for loops. One for loop
> that checks the entry's states, and one for loop that does the actual
> incrementing work (or state modification).
>
> We can check in the first for loop, if it is safe to proceed:
>
> if (!count && !has_cache) {
>     err = -ENOENT;
> } else if (usage == SWAP_HAS_CACHE) {
> if (has_cache)
>     err = -EEXIST;
> } else if ((count & ~COUNT_CONTINUED) > SWAP_MAP_MAX) {
>     err = -EINVAL;
> } else if (usage == 1 && nr > 1 && (count & ~COUNT_CONTINUED) >=
> SWAP_MAP_MAX)) {
>     /* the batched variants currently do not support rollback */
>     err = -ENOMEM;
> }
>
> At this point, IIUC, we have not done any incrementing, so no rollback
> needed? :)

I think that it's better to add a VM_WARN_ONCE() here.  If someone
enabled 'nr > 1' for __swap_duplicate(), the issue will be more
explicit.

[snip]

--
Best Regards,
Huang, Ying