On Thu 26-01-23 09:50:38, Michal Hocko wrote: > On Wed 25-01-23 14:21:35, Minchan Kim wrote: > > On Wed, Jan 25, 2023 at 10:37:59PM +0100, Michal Hocko wrote: > > > On Wed 25-01-23 10:07:49, Minchan Kim wrote: > > > > On Wed, Jan 25, 2023 at 06:07:00PM +0100, Michal Hocko wrote: > > > > > On Wed 25-01-23 08:36:02, Minchan Kim wrote: > > > > > > On Wed, Jan 25, 2023 at 09:04:16AM +0100, Michal Hocko wrote: > > > > > > > On Tue 24-01-23 16:54:57, Minchan Kim wrote: > > > > > > > > madvise LRU manipulation APIs need to scan address ranges to find > > > > > > > > present pages at page table and provides advice hints for them. > > > > > > > > > > > > > > > > Likewise pg[scan/steal] count on vmstat, madvise_pg[scanned/hinted] > > > > > > > > shows the proactive reclaim efficiency so this patch adds those > > > > > > > > two statistics in vmstat. > > > > > > > > > > > > > > > > madvise_pgscanned, madvise_pghinted > > > > > > > > > > > > > > > > Since proactive reclaim using process_madvise(2) as userland > > > > > > > > memory policy is popular(e.g,. Android ActivityManagerService), > > > > > > > > those stats are helpful to know how efficiently the policy works > > > > > > > > well. > > > > > > > > > > > > > > The usecase description is still too vague. What are those values useful > > > > > > > for? Is there anything actionable based on those numbers? How do you > > > > > > > deal with multiple parties using madvise resp. process_madvise so that > > > > > > > their stats are combined? > > > > > > > > > > > > The metric helps monitoing system MM health under fleet and experimental > > > > > > tuning with diffrent policies from the centralized userland memory daemon. > > > > > > > > > > That is just too vague for me to imagine anything more specific then, we > > > > > have numbers and we can show them in a report. What does it actually > > > > > mean that madvise_pgscanned is high. Or that pghinted / pgscanned is > > > > > low (that you tend to manually reclaim sparse mappings)? > > > > > > > > If that's low, it means the userspace daemon's current tune/policy are > > > > inefficient or too aggressive since it is working on address spacess > > > > of processes which don't have enough memory the hint can work(e.g., > > > > shared addresses, cold address ranges or some special address ranges like > > > > VM_PFNMAP) so sometime, we can detect regression to find culprit or > > > > have a chance to look into better ideas to improve. > > > > > > Are you sure this is really meaningful metric? Just consider a large and > > > sparsely populated mapping. This can be a perfect candidate for user > > > space reclaim target (e.g. consider a mapping covering a large matrix > > > or other similar data structure). pghinted/pgscanned would be really > > > small while the reclaim efficiency could be quite high in that case, > > > wouldn't it? > > > > Why do you think it's efficient? It need to spend quite CPU cycle to > > scan a few of pages to evict. I don't see it's efficient if it happens > > quite a lot. > > Because it doesn't really matter how many page tables you have to scan > but how easily you can reclaim the memory behind that. Because it is the > memory that matters. Just consider THP vs. 4k backed address ranges. You > are going to scan much more for latter by design. That doesn't really > mean that this is a worse candidate for reclaim and you should be only > focusing on THP backed mappings. See? > > I suspect you try to mimic pgscan/pgsteal effectivness metric on the dang. I meant pgsteal/pgscan > address space but that is a fundamentally different thing. -- Michal Hocko SUSE Labs
