On Thu 26-01-23 09:10:46, Minchan Kim wrote: > On Thu, Jan 26, 2023 at 09:50:37AM +0100, Michal Hocko wrote: [...] > > I suspect you try to mimic pgscan/pgsteal effectivness metric on the > > address space but that is a fundamentally different thing. > > I don't see anything different, fundamentally. OK, this really explains our disconnect here. Your metric reports nr_page_tables (nr_scanned) and number of aged and potentially reclaimed pages. You do not know whether that reclaim was successful. So you effectively learn how many pages have already been unmapped before your call. Can this be sometimes useful? Probably yes. Does it say anything about the reclaim efficiency? I do not think so. You could have hit pinned pages or countless other conditions why those pages couldn't have been reclaimed and they have stayed mapped after madvise call. pgsteal tells you how many pages from those scanned have been reclaimed. See the difference? Also I do not find information about how many non-present ptes have been scann super interesting. Sure that is a burnt time as well but to me it would be much more valuable information to see how many of those resident could have been actually reclaimed. Because that tells whether your reclaim target was a good choice and IMHO that is a valuable information for user space memory reclaim agent. Again consider a large sparsely mapped memory but mostly inactive memory and a condensed active one with the same rss. The reclaim could have been successful for the former while not on the latter. Your matric would give a rather misleading numbers, don't you think? -- Michal Hocko SUSE Labs
