On Tue, Jul 30, 2024 at 01:11:31AM +1200, Barry Song wrote: > for this zRAM case, it is a new allocated large folio, only > while all conditions are met, we will allocate and map > the whole folio. you can check can_swapin_thp() and > thp_swap_suitable_orders(). YOU ARE DOING THIS WRONGLY! All of you anonymous memory people are utterly fixated on TLBs AND THIS IS WRONG. Yes, TLB performance is important, particularly with crappy ARM designs, which I know a lot of you are paid to work on. But you seem to think this is the only consideration, and you're making bad design choices as a result. It's overly complicated, and you're leaving performance on the table. Look back at the results Ryan showed in the early days of working on large anonymous folios. Half of the performance win on his system came from using larger TLBs. But the other half came from _reduced software overhead_. The LRU lock is a huge problem, and using large folios cuts the length of the LRU list, hence LRU lock hold time. Your _own_ data on how hard it is to get hold of a large folio due to fragmentation should be enough to convince you that the more large folios in the system, the better the whole system runs. We should not decline to allocate large folios just because they can't be mapped with a single TLB!
