On Sun, Oct 27, 2024 at 3:05 PM Vlastimil Babka <vbabka@xxxxxxx> wrote: > > On 10/27/24 21:51, Yu Zhao wrote: > > On Sun, Oct 27, 2024 at 2:36 PM Vlastimil Babka <vbabka@xxxxxxx> wrote: > >> > >> On 10/27/24 21:17, Yu Zhao wrote: > >> > On Sun, Oct 27, 2024 at 1:53 PM Vlastimil Babka <vbabka@xxxxxxx> wrote: > >> >> > >> > >> For example: > >> > >> - a page is on pcplist in MIGRATE_MOVABLE list > >> - we reserve its pageblock as highatomic, which does nothing to the page on > >> the pcplist > >> - page above is flushed from pcplist to zone freelist, but it remembers it > >> was MIGRATE_MOVABLE, merges with another buddy/buddies from the > >> now-highatomic list, the resulting order-X page ends up on the movable > >> freelist despite being in highatomic pageblock. The counter of free > >> highatomic is now wrong wrt the freelist reality > > > > This is the part I don't follow: how is it wrong w.r.t. the freelist > > reality? The new nr_free_highatomic should reflect how many pages are > > exactly on free_list[MIGRATE_HIGHATOMIC], because it's updated > > accordingly. > > You'd have to try implementing your change in the kernel without that > migratetype hygiene series, and see how it would either not work, or you'd > end up implementing the series as part of that. A proper backport would need to track the MT of the free_list a page is deleted from, and I see no reason why in such a proper backport "the counter could drift easily" or "the counter of free highatomic is now wrong wrt the freelist reality". So I assume you actually mean this patch can't be backported cleanly? (Which I do agree.)
