'kern.maxpipekva exceeded' messages...

Mike Silbersack silby at silby.com
Tue Jan 27 08:25:28 PST 2004

On Tue, 27 Jan 2004, Dag-Erling [iso-8859-1] Smørgrav wrote:

> Mike Silbersack <silby at silby.com> writes:
> > Documenting maxpipekva / reducing pipe memory usage is on my to-do list.
> > Unfortunately, I was unable to complete my changes in time for
> > 5.2-release; I will try to get them in place soon.
> We seem to have had a regression in this area since 5.1-RELEASE.
> Systems that ran fine on 5.1-RELEASE are running out of pipe kva after
> an upgrade to 5.2-CURRENT.  Should we suspect a leak somewhere?

I do not believe that there is a leak.  What actually happened is that
between 5.1 and 5.2 I added pipe memory limits, which had not been present
before.  This is suboptimal for two reasons:

1.  Pipes overallocate memory greatly; I could probably reduce the memory
usage of an idle pipe by 8x or so.

2.  At Alan's request (due to locking issues), I moved the pipes into
their own submap of the kernel map, rather than having them allocated out
of the main map itself;  this required me to put an even larger cap on
pipe memory usage, as I did not want to steal too much from the main
kernel map.  I'll drop Alan a line and see if the locking situation has
changed since that time.

If you're interested in working on this right now, I can send you what I
had planned to do for #1, it would be a very small amount of code,
although it would require a bit of testing to ensure that it does not
degrade the performance of pipes by a noticeable amount.

Mike "Silby" Silbersack

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