On Thu, Apr 21, 2022 at 03:44:02PM +0200, Alexander Leidinger wrote: | Quoting Mateusz Guzik <mjgu...@gmail.com> (from Thu, 21 Apr 2022 | 14:50:42 +0200): | | > On 4/21/22, Alexander Leidinger <alexan...@leidinger.net> wrote: | >> I tried nocache on a system with a lot of jails which use nullfs, | >> which showed very slow behavior in the daily periodic runs (12h runs | >> in the night after boot, 24h or more in subsequent nights). Now the | >> first nightly run after boot was finished after 4h. | >> | >> What is the benefit of not disabling the cache in nullfs? I would | >> expect zfs (or ufs) to cache the (meta)data anyway. | >> | > | > does the poor performance show up with | > https://people.freebsd.org/~mjg/vnlru_free_pick.diff ? | | I would like to have all the 22 jails run the periodic scripts a | second night in a row before trying this. | | > if the long runs are still there, can you get some profiling from it? | > sysctl -a before and after would be a start. | >| > My guess is that you are the vnode limit and bumping into the 1 second sleep.| | That would explain the behavior I see since I added the last jail | which seems to have crossed a threshold which triggers the slow | behavior. | | Current status (with the 112 nullfs mounts with nocache): | kern.maxvnodes: 10485760 | kern.numvnodes: 3791064 | kern.freevnodes: 3613694 | kern.cache.stats.heldvnodes: 151707 | kern.vnodes_created: 260288639 | | The maxvnodes value is already increased by 10 times compared to the | default value on this system.I've attached mount.patch that when doing mount -v should show the vnode usage per filesystem. Note that the problem I was running into was after some operations arc_prune and arc_evict would consume 100% of 2 cores and make ZFS really slow. If you are not running into that issue then nocache etc. shouldn't be needed.
I don't run into this issue, but I have a huge perf difference when using nocache in the nightly periodic runs. 4h instead of 12-24h (22 jails on this system).
On my laptop I set ARC to 1G since I don't use swap and in the past ARC would consume to much memory and things would die. When the nullfs holds a bunch of vnodes then ZFS couldn't release them. FYI, on my laptop with nocache and limited vnodes I haven't run into this problem. I haven't tried the patch to let ZFS free it's and nullfs vnodes on my laptop. I have only tried it via
I have this patch and your mount patch installed now, without nocache and reduced arc reclaim settings (100, 1). I will check the runtime for the next 2 days.
Your mount patch to show the per mount vnodes count looks useful, not only for this particular case. Do you intend to commit it?
Bye, Alexander. -- http://www.Leidinger.net alexan...@leidinger.net: PGP 0x8F31830F9F2772BF http://www.FreeBSD.org netch...@freebsd.org : PGP 0x8F31830F9F2772BF
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