On Wed 04-03-20 19:15:20, Huang, Ying wrote: > Michal Hocko <mhocko@xxxxxxxxxx> writes: > > > On Tue 03-03-20 19:49:53, Huang, Ying wrote: [...] > >> Because the penalty difference is so large, I > >> think it may be a good idea to always put clean MADV_FREE pages at the > >> tail of the inactive file LRU list? > > > > You are again making assumptions without giving any actual real > > examples. Reconstructing MADV_FREE pages cost can differ a lot. > > In which situation the cost to reconstruct MADV_FREE pages can be higher > than the cost to allocate file cache page and read from disk? Heavy > contention on mmap_sem? Allocating a page might be really costly but even without that. Reconstructnig the content of the page can be really high and actually much larger than an IO to get a page from the storage. Consider decompression or some other transformations to get the content. Userspace has means to detect that the content is still up-to-date as already has been mentioned so all those steps can be avoided. -- Michal Hocko SUSE Labs
