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From: mike@hpcupt1.cup.hp.com (Michael Saboff)
Newsgroups: comp.sys.hp
Subject: Re: Kernel message... Cannot allocate fs buffers
Message-ID: <67870017@hpcupt1.cup.hp.com>
Date: 30 Apr 91 00:16:39 GMT
References: <3833@dali>
Organization: Hewlett Packard, Cupertino
Lines: 35

> I'm seeing frequent (every few days) hangs of my machine with the following
> on the console:
>
> Failed kernel selftest.  Failures:
> Cannot allocate file system buffers
>
> And it repeats it self every 2 minutes.  I don't have a wildly different
> kernel config from when I was running 6.0.  I do use the -async option 
> in my exports file for NFS, but I doubt that has anything to do with it.
>
> Any suggestions on kernel params to change?  Or a clue as to what might be
> going on?

Sorry for the length, but I want to tell what is happening as well as
how to fix it.

The problem is with the diskless subsytem and its tuneables.  This
message is output as part of the regular (every 2 minutes) self test of
the diskless subsytem.  There is a small pool of file system buffers
that is used for diskless requests.  This pool is different from the
normal "nbuf" pool in that allocation from this pool can be done from an
interrupt handler.  What's happening is that the selftest code cannot
allocate one of these buffers.  On your system, this pool is too small
and diskless requests are not being handled because of this (hang).

The kernel tuneable in question is called "dskless_fsbufs".  This
tuneable has usually set to be the same as "serving_array_size".  If you
system is a server, this is probably 200.  I suspect that your system is
a cluster client and that serving_array_size is real small (0-10).
Change serving_array_size to be 20 or so (either directly or via other
kernel tuneables it depends on like maxusers).  Check /etc/master for
default settings.

Michael Saboff           Member of Filesystem Project - HP-UX Kernel Lab
mike@hpda.hp.com