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

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

On Tue, 16 May 2017, Joerg Sonnenberger wrote:

> On Tue, May 16, 2017 at 08:12:20AM +0800, Paul Goyette wrote:
> > * xosview frequently reports that the system is running at near-100%
> >   in SYS time.
>
> 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.  :(


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