Messages in this thread | | | Subject | Re: INFO: rcu_sched detected stalls on CPUs/tasks with `kswapd` and `mem_cgroup_shrink_node` | From | Donald Buczek <> | Date | Thu, 24 Nov 2016 19:50:51 +0100 |
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On 24.11.2016 11:15, Michal Hocko wrote:
> On Mon 21-11-16 16:35:53, Donald Buczek wrote: > [...] >> Hello, >> >> thanks a lot for looking into this! >> >> Let me add some information from the reporting site: >> >> * We've tried the patch from Paul E. McKenney (the one posted Wed, 16 Nov >> 2016) and it doesn't shut up the rcu stall warnings. >> >> * Log file from a boot with the patch applied ( grep kernel >> /var/log/messages ) is here : >> http://owww.molgen.mpg.de/~buczek/321322/2016-11-21_syslog.txt >> >> * This system is a backup server and walks over thousands of files sometimes >> with multiple parallel rsync processes. >> >> * No rcu_* warnings on that machine with 4.7.2, but with 4.8.4 , 4.8.6 , >> 4.8.8 and now 4.9.0-rc5+Pauls patch > I assume you haven't tried the Linus 4.8 kernel without any further > stable patches? Just to be sure we are not talking about some later > regression which found its way to the stable tree. > >> * When the backups are actually happening there might be relevant memory >> pressure from inode cache and the rsync processes. We saw the oom-killer >> kick in on another machine with same hardware and similar (a bit higher) >> workload. This other machine also shows a lot of rcu stall warnings since >> 4.8.4. >> >> * We see "rcu_sched detected stalls" also on some other machines since we >> switched to 4.8 but not as frequently as on the two backup servers. Usually >> there's "shrink_node" and "kswapd" on the top of the stack. Often >> "xfs_reclaim_inodes" variants on top of that. > I would be interested to see some reclaim tracepoints enabled. Could you > try that out? At least mm_shrink_slab_{start,end} and > mm_vmscan_lru_shrink_inactive. This should tell us more about how the > reclaim behaved.
We'll try that tomorrow!
Donald
-- Donald Buczek buczek@molgen.mpg.de Tel: +49 30 8413 1433
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