> > > > 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. > > > > > Back to the beginning, lru_add_drain() is the simplest option，which is common > > below the __read_swap_cache_async(). Please see the function > > swap_cluster_readahead() > > and swap_vma_readahead(), of course it has been batched. > > > > Or we should leave this problem alone，before we can write back zswap > > in batches. > > Calling lru_add_drain() for every written back page is an overkill > imo. If we have writeback batching at some point, it may make more > sense then. Agree. > > Adding Michal Hocko was recently complaining [1] about lru_add_drain() > being called unnecessarily elsewhere. Got it, thanks. > > [1]https://lore.kernel.org/linux-mm/ZaD9BNtXZfY2UtVI@tiehlicka/
