Hello Weikuan, I did not look at the code closely enough to tell how things work now, but I can comment how I believe they should work. (Any corrections of my false expectations are very welcome.) My believes are as follows: > how cachefs could be useful for the type of netfs' that use page > cache but not local disk caches. It cannot. Thought in theory one could very well setup cachefs on a RAM-based block device, this might make sense only in very special circumstances when, given a particular file-access pattern, the cachefs caching strategy happens to be better than the usual page-cache used for files. (Maybe that due to some kernel optimizations this 'competition' even does not happen?) > a) if the page in the cachefs is still valid (up-to-date), would it > still be in the page-cache? If so, reading from cachefs would not be > efficient then. Maybe it is in the page-cache, maybe not. If yes, it is used (I hope). > b) Is it possible that the page is already evicted from pagecache, but > it is still in the cachefs? Yes, for example after client's reboot. > when trying to read from pagecache or cachefs, is it > guaranteed that the cached file page is not out-of-date w.r.t the copy > at the server side. I believe it is guaranteed to the same level as NFS itself can guarantee this. Some metadata have to be got from the server to achieve this. > I might have just asked some naive questions. Please bear with me. But > they puzzle me quite a bit. I added my believes about the design goals. I guess more people could share these believes with me, so it is worth correcting them if they are wrong. Regards Vaclav
