Can you share the fio job file that you utilized so I can attempt to repeat locally? On Tue, May 2, 2017 at 2:51 AM, nick <nick@xxxxxxx> wrote: > Hi Jason, > thanks for your feedback. I did now some tests over the weekend to verify the > memory overhead. > I was using qemu 2.8 (taken from the Ubuntu Cloud Archive) with librbd 10.2.7 > on Ubuntu 16.04 hosts. I suspected the ceph rbd cache to be the cause of the > overhead so I just generated a lot of IO with the help of fio in the VMs (with > a datasize of 80GB) . All VMs had 3GB of memory. I had to run fio multiple > times, before reaching high RSS values. > I also noticed that when using larger blocksizes during writes (like 4M) the > memory overhead in the KVM process increased faster. > I ran several fio tests (one after another) and the results are: > > KVM with writeback RBD cache: max. 85% memory overhead (2.5 GB overhead) > KVM with writethrough RBD cache: max. 50% memory overhead > KVM without RBD caching: less than 10% overhead all the time > KVM with local storage (logical volume used): 8% overhead all the time > > I did not reach those >200% memory overhead results that we see on our live > cluster, but those virtual machines have a way longer uptime as well. > > I also tried to reduce the RSS memory value with cache dropping on the > physical host and in the VM. Both did not lead to any change. A reboot of the > VM also does not change anything (reboot in the VM, not a new KVM process). > The only way to reduce the RSS memory value is a live migration so far. Might > this be a bug? The memory overhead sounds a bit too much for me. > > Best Regards > Sebastian > > > On Thursday, April 27, 2017 10:08:36 AM you wrote: >> I know we noticed high memory usage due to librados in the Ceph >> multipathd checker [1] -- the order of hundreds of megabytes. That >> client was probably nearly as trivial as an application can get and I >> just assumed it was due to large monitor maps being sent to the client >> for whatever reason. Since we changed course on our RBD iSCSI >> implementation, unfortunately the investigation into this high memory >> usage fell by the wayside. >> >> [1] >> http://git.opensvc.com/gitweb.cgi?p=multipath-tools/.git;a=blob;f=libmultip >> ath/checkers/rbd.c;h=9ea0572f2b5bd41b80bf2601137b74f92bdc7278;hb=HEAD >> On Thu, Apr 27, 2017 at 5:26 AM, nick <nick@xxxxxxx> wrote: >> > Hi Christian, >> > thanks for your answer. >> > The highest value I can see for a local storage VM in our infrastructure >> > is a memory overhead of 39%. This is big, but the majority (>90%) of our >> > local storage VMs are using less than 10% memory overhead. >> > For ceph storage based VMs this looks quite different. The highest value I >> > can see currently is 244% memory overhead. So that specific allocated 3GB >> > memory VM is using now 10.3 GB RSS memory on the physical host. This is a >> > really huge value. In general I can see that the majority of the ceph >> > based VMs has more than 60% memory overhead. >> > >> > Maybe this is also a bug related to qemu+librbd. It would be just nice to >> > know if other people are seeing those high values as well. >> > >> > Cheers >> > Sebastian >> > >> > On Thursday, April 27, 2017 06:10:48 PM you wrote: >> >> Hello, >> >> >> >> Definitely seeing about 20% overhead with Hammer as well, so not version >> >> specific from where I'm standing. >> >> >> >> While non-RBD storage VMs by and large tend to be closer the specified >> >> size, I've seen them exceed things by few % at times, too. >> >> For example a 4317968KB RSS one that ought to be 4GB. >> >> >> >> Regards, >> >> >> >> Christian >> >> >> >> On Thu, 27 Apr 2017 09:56:48 +0200 nick wrote: >> >> > Hi, >> >> > we are running a jewel ceph cluster which serves RBD volumes for our >> >> > KVM >> >> > virtual machines. Recently we noticed that our KVM machines use a lot >> >> > more >> >> > memory on the physical host system than what they should use. We >> >> > collect >> >> > the data with a python script which basically executes 'virsh >> >> > dommemstat >> >> > <virtual machine name>'. We also verified the results of the script >> >> > with >> >> > the memory stats of 'cat /proc/<kvm PID>/status' for each virtual >> >> > machine >> >> > and the results are the same. >> >> > >> >> > Here is an excerpt for one pysical host where all virtual machines are >> >> > running since yesterday (virtual machine names removed): >> >> > >> >> > """ >> >> > overhead actual percent_overhead rss >> >> > ---------- -------- ---------------- -------- >> >> > 423.8 MiB 2.0 GiB 20 2.4 GiB >> >> > 460.1 MiB 4.0 GiB 11 4.4 GiB >> >> > 471.5 MiB 1.0 GiB 46 1.5 GiB >> >> > 472.6 MiB 4.0 GiB 11 4.5 GiB >> >> > 681.9 MiB 8.0 GiB 8 8.7 GiB >> >> > 156.1 MiB 1.0 GiB 15 1.2 GiB >> >> > 278.6 MiB 1.0 GiB 27 1.3 GiB >> >> > 290.4 MiB 1.0 GiB 28 1.3 GiB >> >> > 291.5 MiB 1.0 GiB 28 1.3 GiB >> >> > 0.0 MiB 16.0 GiB 0 13.7 GiB >> >> > 294.7 MiB 1.0 GiB 28 1.3 GiB >> >> > 135.6 MiB 1.0 GiB 13 1.1 GiB >> >> > 0.0 MiB 2.0 GiB 0 1.4 GiB >> >> > 1.5 GiB 4.0 GiB 37 5.5 GiB >> >> > """ >> >> > >> >> > We are using the rbd client cache for our virtual machines, but it is >> >> > set >> >> > to only 128MB per machine. There is also only one rbd volume per >> >> > virtual >> >> > machine. We have seen more than 200% memory overhead per KVM machine on >> >> > other physical machines. After a live migration of the virtual machine >> >> > to >> >> > another host the overhead is back to 0 and increasing slowly back to >> >> > high >> >> > values. >> >> > >> >> > Here are our ceph.conf settings for the clients: >> >> > """ >> >> > [client] >> >> > rbd cache writethrough until flush = False >> >> > rbd cache max dirty = 100663296 >> >> > rbd cache size = 134217728 >> >> > rbd cache target dirty = 50331648 >> >> > """ >> >> > >> >> > We noticed this behavior since we are using the jewel librbd libraries. >> >> > We >> >> > did not encounter this behavior when using the ceph infernalis librbd >> >> > version. We also do not see this issue when using local storage, >> >> > instead >> >> > of ceph. >> >> > >> >> > Some version information of the physical host which runs the KVM >> >> > machines: >> >> > """ >> >> > OS: Ubuntu 16.04 >> >> > kernel: 4.4.0-75-generic >> >> > librbd: 10.2.7-1xenial >> >> > """ >> >> > >> >> > We did try to flush and invalidate the client cache via the ceph admin >> >> > socket, but this did not change any memory usage values. >> >> > >> >> > Does anyone encounter similar issues or does have an explanation for >> >> > the >> >> > high memory overhead? >> >> > >> >> > Best Regards >> >> > Sebastian >> > >> > -- >> > Sebastian Nickel >> > Nine Internet Solutions AG, Albisriederstr. 243a, CH-8047 Zuerich >> > Tel +41 44 637 40 00 | Support +41 44 637 40 40 | www.nine.ch >> > _______________________________________________ >> > ceph-users mailing list >> > ceph-users@xxxxxxxxxxxxxx >> > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com > > -- > Sebastian Nickel > Nine Internet Solutions AG, Albisriederstr. 243a, CH-8047 Zuerich > Tel +41 44 637 40 00 | Support +41 44 637 40 40 | www.nine.ch -- Jason _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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