Le vendredi 18 septembre 2015 à 12:04 +0200, Jan Schermer a écrit : > > On 18 Sep 2015, at 11:28, Christian Balzer <ch...@gol.com> wrote: > > > > On Fri, 18 Sep 2015 11:07:49 +0200 Olivier Bonvalet wrote: > > > > > Le vendredi 18 septembre 2015 à 10:59 +0200, Jan Schermer a écrit > > > : > > > > In that case it can either be slow monitors (slow network, slow > > > > disks(!!!) or a CPU or memory problem). > > > > But it still can also be on the OSD side in the form of either > > > > CPU > > > > usage or memory pressure - in my case there were lots of memory > > > > used > > > > for pagecache (so for all intents and purposes considered > > > > "free") but > > > > when peering the OSD had trouble allocating any memory from it > > > > and it > > > > caused lots of slow ops and peering hanging in there for a > > > > while. > > > > This also doesn't show as high CPU usage, only kswapd spins up > > > > a bit > > > > (don't be fooled by its name, it has nothing to do with swap in > > > > this > > > > case). > > > > > > My nodes have 256GB of RAM (for 12x300GB ones) or 128GB of RAM > > > (for > > > 4x800GB ones), so I will try track this too. Thanks ! > > > > > I haven't seen this (known problem) with 64GB or 128GB nodes, > > probably > > because I set /proc/sys/vm/min_free_kbytes to 512MB or 1GB > > respectively. > > > > I had this set to 6G and that doesn't help. This "buffer" is probably > only useful for some atomic allocations that can use it, not for > userland processes and their memory. Or maybe they get memory from > this pool but it gets replenished immediately. > QEMU has no problem allocating 64G on the same host, OSD struggles to > allocate memory during startup or when PGs are added during > rebalancing - probably because it does a lot of smaller allocations > instead of one big. >
For now I dropped cache *and* set min_free_kbytes to 1GB. I don't throw any rebalance, but I can see a reduced filestore.commitcycle_latency. _______________________________________________ ceph-users mailing list ceph-users@lists.ceph.com http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
