On 10/28/24 1:24 AM, Yu Zhao wrote: > 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.) Yes you're right. But since we don't plan to backport it beyond 6.12, sorry for sidetracking the discussion unnecessarily. More importantly, is it possible to change the implementation as I suggested? [1] Hooking to __del_page_from_free_list() and __add_to_free_list() means extra work in every loop iteration in expand() and __free_one_page(). The migratetype hygiene should ensure it's not necessary to intercept every freelist add/move and hooking to account_freepages() should be sufficient and in line with the intended design. Thanks, Vlastimil [1] https://lore.kernel.org/all/37a28ef7-e477-40b0-a8e4-3d74b747e323@xxxxxxx/
