On Fri, 17 Jan 2020, Kirill Tkhai wrote: > >> I think that's a good point, especially considering that the current code > >> appears to unconditionally place any compound page on the deferred split > >> queue of the destination memcg. The correct list that it should appear > >> on, I believe, depends on whether the pmd has been split for the process > >> being moved: note the MC_TARGET_PAGE caveat in > >> mem_cgroup_move_charge_pte_range() that does not move the charge for > >> compound pages with split pmds. So when mem_cgroup_move_account() is > >> called with compound == true, we're moving the charge of the entire > >> compound page: why would it appear on that memcg's deferred split queue? > > > > I believe Kirill asked how do we know that the page should be actually > > added to the deferred list just from the list_empty check. In other > > words what if the page hasn't been split at all? > > Yes, I'm talking about this. Function mem_cgroup_move_account() adds every > huge page to the deferred list, while we need to do that only for pages, > which are queued for splitting... > Yup, and that appears broken before Wei's patch. Since we only migrate charges of entire compound pages (we have a mapping pmd, the underlying page cannot be split), it should not appear on the deferred split queue for any memcg, right?
