On Thu, Aug 18, 2016 at 7:26 PM, Minchan Kim <minchan@xxxxxxxxxx> wrote: > Hi Michal, > > On Thu, Aug 18, 2016 at 08:01:04PM +0200, Michal Hocko wrote: >> On Thu 18-08-16 10:47:57, Sonny Rao wrote: >> > On Thu, Aug 18, 2016 at 12:44 AM, Michal Hocko <mhocko@xxxxxxxxxx> wrote: >> > > On Wed 17-08-16 11:57:56, Sonny Rao wrote: >> [...] >> > >> 2) User space OOM handling -- we'd rather do a more graceful shutdown >> > >> than let the kernel's OOM killer activate and need to gather this >> > >> information and we'd like to be able to get this information to make >> > >> the decision much faster than 400ms >> > > >> > > Global OOM handling in userspace is really dubious if you ask me. I >> > > understand you want something better than SIGKILL and in fact this is >> > > already possible with memory cgroup controller (btw. memcg will give >> > > you a cheap access to rss, amount of shared, swapped out memory as >> > > well). Anyway if you are getting close to the OOM your system will most >> > > probably be really busy and chances are that also reading your new file >> > > will take much more time. I am also not quite sure how is pss useful for >> > > oom decisions. >> > >> > I mentioned it before, but based on experience RSS just isn't good >> > enough -- there's too much sharing going on in our use case to make >> > the correct decision based on RSS. If RSS were good enough, simply >> > put, this patch wouldn't exist. >> >> But that doesn't answer my question, I am afraid. So how exactly do you >> use pss for oom decisions? > > My case is not for OOM decision but I agree it would be great if we can get > *fast* smap summary information. > > PSS is really great tool to figure out how processes consume memory > more exactly rather than RSS. We have been used it for monitoring > of memory for per-process. Although it is not used for OOM decision, > it would be great if it is speed up because we don't want to spend > many CPU time for just monitoring. > > For our usecase, we don't need AnonHugePages, ShmemPmdMapped, Shared_Hugetlb, > Private_Hugetlb, KernelPageSize, MMUPageSize because we never enable THP and > hugetlb. Additionally, Locked can be known via vma flags so we don't need it, > either. Even, we don't need address range for just monitoring when we don't > investigate in detail. > > Although they are not severe overhead, why does it emit the useless > information? Even bloat day by day. :( With that, userspace tools should > spend more time to parse which is pointless. > > Having said that, I'm not fan of creating new stat knob for that, either. > How about appending summary information in the end of smap? > So, monitoring users can just open the file and lseek to the (end - 1) and > read the summary only. > That would work fine for us as long as it's fast -- i.e. we don't still have to do all the expensive per-VMA format conversion in the kernel. > Thanks. -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
