Re: Problem with lots of (perhaps too much?) memory

[Paul Goyette <paul%whooppee.com@localhost>]

On Wed, 17 May 2017, J. Hannken-Illjes wrote:

> > > Chances are very high that you are hitting the free page lock contention
> > > bug.
> >
> > Further observation:
> >
> > 1. A run of lockstat shows that there's lots of activity on
> >   mntvnode_lock from vfs_insmntque
> >
> > 2. The problem can be triggered simply by running 'du -s' on a
> >   file system with lots of files (for example, after having run
> >   'build.sh release' for ~40 different architectures, and having
> >   kept ALL of the obj/*, dest/*, and release/* output files).
> >
> > 3. The ioflush thread _never_ finishes.  Even 12 hours after the
> >   trigger, and after an 8-hour sleep window doing nothing (other
> >   than receiving a couple dozen Emails), the ioflush thread is
> >   still using 5-10% of one CPU core/thread.
> >
> > 4. If I umount the trigger file system, ioflush time goes to near-
> >   zero.  I can remount without problem, however shortly after
> >   re-running the 'du -s' command the problem returns.
> >
> > There was a comment on IRC that yamt@ had been working on a problem where "ioflush wastes a lot of CPU time when there are lots of vnodes" seems to describe this situation.  Unfortunately, it seems that yamt never finished working on the problem.  :(
>
> Two questions:
>
> - What is the size of your vnode cache (sysctl kern.maxvnodes)?

kern.maxvnodes = 6706326


> - Is the vdrain thread using CPU too?

No, vdrain appears totally idle.


+------------------+--------------------------+----------------------------+
| Paul Goyette     | PGP Key fingerprint:     | E-mail addresses:          |
| (Retired)        | FA29 0E3B 35AF E8AE 6651 | paul at whooppee dot com   |
| Kernel Developer | 0786 F758 55DE 53BA 7731 | pgoyette at netbsd dot org |
+------------------+--------------------------+----------------------------+