On Thu 02-03-17 09:01:01, Johannes Weiner wrote: > On Wed, Mar 01, 2017 at 07:57:35PM +0100, Michal Hocko wrote: > > On Wed 01-03-17 13:31:49, Johannes Weiner wrote: [...] > > > The error when reading a specific smaps should be completely ok. > > > > > > In numbers: even if your process is madvising from 16 different CPUs, > > > the error in its smaps file will peak at 896K in the worst case. That > > > level of concurrency tends to come with much bigger memory quantities > > > for that amount of error to matter. > > > > It is still an unexpected behavior IMHO and an implementation detail > > which leaks to the userspace. > > We have per-cpu fuzz in every single vmstat counter. Look at > calculate_normal_threshold() in vmstat.c and the sample thresholds for > when per-cpu deltas are flushed. In the vast majority of machines, the > per-cpu error in these counters is much higher than what we get with > pagevecs holding back a few pages. Yes but vmstat counters have a different usecase AFAIK. You mostly look at those when debugging or watching the system. /proc/<pid>/smaps is quite often used to do per task metrics which are then used for some decision making so it should be less fuzzy if that is possible. > It's not that I think you're wrong: it *is* an implementation detail. > But we take a bit of incoherency from batching all over the place, so > it's a little odd to take a stand over this particular instance of it > - whether demanding that it'd be fixed, or be documented, which would > only suggest to users that this is special when it really isn't etc. I am not aware of other counter printed in smaps that would suffer from the same problem, but I haven't checked too deeply so I might be wrong. Anyway it seems that I am alone in my position so I will not insist. If we have any bug report then we can still fix it. -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
