Re: Gluster High CPU/Clients Hanging on Heavy Writes

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Hi Yuhao, 

On Mon, 6 Aug 2018, 15:26 Yuhao Zhang, <zzyzxd@xxxxxxxxx> wrote:
Hello,

I just experienced another hanging one hour ago and the server was not even under heavy IO.

Atin, I attached the process monitoring results and another statedump.

Xavi, ZFS was fine, during the hanging, I can still write directly to the ZFS volume. My ZFS version: ZFS: Loaded module v0.6.5.6-0ubuntu16, ZFS pool version 5000, ZFS filesystem version 5

I highly recommend you to upgrade to version 0.6.5.8 at least. It fixes a kernel panic that can happen when used with gluster. However this is not your current problem.

Top statistics show low available memory and high CPU utilization of kswapd process (along with one of the gluster processes). I've seen frequent memory management problems with ZFS. Have you configured any ZFS parameters? It's highly recommendable to tweak some memory limits.

If that were the problem, there's one thing that should alleviate it (and see if it could be related):

echo 3 >/proc/sys/vm/drop_caches

This should be done on all bricks from time to time. You can wait until the problem appears, but in this case the recovery time can be larger. 

I think this should fix the high CPU usage of kswapd. If so, we'll need to tweak some ZFS parameters.

I'm not sure if the high CPU usage of gluster could be related to this or not.

Xavi

Thank you,
Yuhao
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