On Fri, Feb 10, 2023 at 12:29:54PM +0100, Jan Kara wrote: > functionally that would make sense but as I've mentioned in my reply to you > [1], the problem here is the performance. I've now dug out the discussion > from 2018 where John actually tried to take pinned pages out of the LRU [2] > and the result was 20% IOPS degradation on his NVME drive because of the > cost of taking the LRU lock. I'm not even speaking how costly that would > get on any heavily parallel direct IO workload on some high-iops device... I think we need to distinguish between short- and long terms pins. For short term pins like direct I/O it doesn't make sense to take them off the lru, or to do any other special action. Writeback will simplify have to wait for the short term pin. Long-term pins absolutely would make sense to be taken off the LRU list.
