Re: ceph node crashed with these errors "kernel: ceph: build_snap_context" (maybe now it is urgent?)

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 >
 >>  >
 >>  >ISTR there were some anti-spam measures put in place.  Is your 
account
 >>  >waiting for manual approval?  If so, David should be able to help.
 >>
 >> Yes if I remember correctly I get waiting approval when I try to log 
in.
 >>
 >>  >>
 >>  >>
 >>  >>
 >>  >> Dec 1 03:14:36 c04 kernel: ceph: build_snap_context 100020c9287
 >>  >> ffff911a9a26bd00 fail -12
 >>  >> Dec 1 03:14:36 c04 kernel: ceph: build_snap_context 100020c9283
 >>  >
 >>  >
 >>  >It is failing to allocate memory.  "low load" isn't very specific,
 >>  >can you describe the setup and the workload in more detail?
 >>
 >> 4 nodes (osd, mon combined), the 4th node has local cephfs mount, 
which
 >> is rsync'ing some files from vm's. 'low load' I have sort of test 
setup,
 >> going to production. Mostly the nodes are below a load of 1 (except 
when
 >> the concurrent rsync starts)
 >>
 >>  >How many snapshots do you have?
 >>
 >> Don't know how to count them. I have script running on a 2000 dirs. 
If
 >> one of these dirs is not empty it creates a snapshot. So in theory I
 >> could have 2000 x 7 days = 14000 snapshots.
 >> (btw the cephfs snapshots are in a different tree than the rsync is
 >> using)
 >
 >Is there a reason you are snapshotting each directory individually
 >instead of just snapshotting a common parent?

Yes because I am not sure the snapshot frequency on all folders is going 
to be the same.

 >If you have thousands of snapshots, you may eventually hit a different
 >bug:
 >
 >https://tracker.ceph.com/issues/21420
 >https://docs.ceph.com/docs/master/cephfs/experimental-features/#snapsh
ots
 >
 >Be aware that each set of 512 snapshots amplify your writes by 4K in
 >terms of network consumption.  With 14000 snapshots, a 4K write would
 >need to transfer ~109K worth of snapshot metadata to carry itself out.
 >
 
Also when I am not even writing to a tree with snapshots enabled? I am 
rsyncing to dir3

.
├── dir1
│   ├── dira
│   │   └── .snap
│   ├── dirb
│   ├── dirc
│   │   └── .snap
│   └── dird
│       └── .snap
├── dir2
└── dir3
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