On 2017年09月15日 22:28, Michal Hocko wrote: > On Fri 15-09-17 07:16:23, Dave Hansen wrote: >> On 09/15/2017 04:49 AM, Michal Hocko wrote: >>> Why do we need an auto-mode? Is it safe to enforce by default. >> >> Do we *need* it? Not really. >> >> But, it does offer the best of both worlds: The vast majority of users >> see virtually no impact from the counters. The minority that do need >> them pay the cost *and* don't have to change their tooling at all. > > Just to make it clear, I am not really opposing. It just adds some code > which we can safe... It is also rather chatty for something that can be > true/false. > It has benefit, as Dave mentioned above. Actually, it adds some coding complexity to provide a tuning interface with on/off/auto mode. Using human-readable string instead of magic number makes it easier to use, people probably don't need to review the ABI doc again before using it. So, I don't think that should be a problem >>> Is it> possible that userspace can get confused to see 0 NUMA stats in >> the >>> first read while other allocation stats are non-zero? >> >> I doubt it. Those counters are pretty worthless by themselves. I have >> tooling that goes and reads them, but it aways displays deltas. Read >> stats, sleep one second, read again, print the difference. > > This is how I use them as well. > >> The only scenario I can see mattering is someone who is seeing a >> performance issue due to NUMA allocation misses (or whatever) and wants >> to go look *back* in the past. > > yes > If it really matters, setting vmstat_mode=strict as a default option is a simple way to fix it. What's your idea? thanks >> A single-time printk could also go a long way to keeping folks from >> getting confused. >
