On Thu, Sep 23, 2021 at 06:11:19PM -0700, Yang Shi wrote: > On Thu, Sep 23, 2021 at 4:49 PM Hugh Dickins <hughd@xxxxxxxxxx> wrote: > > I believe Yang Shi is right insofar as the decision on whether it's worth > > queuing for deferred split is being done based on those subpage _mapcounts. > > That is a use I had not considered, and I've given no thought to how > > important or not it is. > > Anyway deferred split is anon THP specific. We don't have to worry > about this for file THP. So your suggestion about just counting total > mapcount seems feasible to me for file THP at least. But I think we probably *should* do deferred split for file THP. At the moment, when we truncate to the middle of a shmem THP, we try a few times to split it and then just give up. We should probably try once and then queue it for deferred split.
