On Wed, Jan 17, 2024 at 1:53 AM Zhongkun He <hezhongkun.hzk@xxxxxxxxxxxxx> wrote: > > > > > > > Please forgive me for adding additional information about this patch. > > > > > > I have finished the opt for introducing a folio_add_lru_tail(), but > > > there are many > > > questions: > > > 1) A new page can be move to LRU only by lru_add_fn, so > > > folio_add_lru_tail could not add pages to LRU for the following code > > > in folio_batch_move_lru(),which is added by Alex Shi for > > > serializing memcg changes in pagevec_lru_move_fn[1]. > > > > > > /* block memcg migration while the folio moves between lru */ > > > if (move_fn != lru_add_fn && !folio_test_clear_lru(folio)) > > > continue; > > > To achieve the goal, we need to add a new function like lru_add_fn > > > which does not have the lru flag and folio_add_lru_tail() > > > + if (move_fn != lru_add_fn && move_fn != lru_move_tail_fn_new && > > > + !folio_test_clear_lru(folio)) > > > > > > 2) __read_swap_cache_async has six parameters, so there is no space to > > > add a new one, add_to_lru_head. > > > > > > So it seems a bit hacky just for a special case for the reasons above. > > > > It's a lot of plumbing for sure. Adding a flag to current task_struct > > is a less-noisy yet-still-hacky solution. I am not saying we should do > > it, but it's an option. I am not sure how much task flags we have to > > spare. > > Got it. Actually this won't really work. Writebak can be asynchronous, so there would be no logical place to unset the flag.
