To: linux-kernel@vger.kernel.org
From: Ed Swierk <eswierk@cs.stanford.edu>
Subject: VFS: file-max limit reached when running on a virtual machine
Date: Thu, 19 Jan 2006 04:19:24 +0000 (UTC)
Message-ID: <loom.20060119T045624-92@post.gmane.org>
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I'm getting the error "VFS: file-max limit 50905 reached" on kernels 2.6.14 and
2.6.15, running on a qemu virtual machine configured with 512 MB of memory.  The
error occurs when I build a relatively large C++ program (the Boost library) on
the VM (which is otherwise idle).  It does not occur on kernels 2.6.11 or 2.6.13.

I understand that changes have been made recently to the way the kernel manages
file descriptors in order to improve real-time performance.

A thread back in October discussing these changes (subject: "VFS: file-max limit
50044 reached") seems to indicate that bad things can happen if certain
callbacks don't get called at regular intervals.  This situation seems quite
likely in a virtual machine environment where the frequency of timer interrupts
might vary by orders of magnitude depending on the workload of the host machine.

I have attempted a few workarounds, to no avail:

* increasing file-max (echo 100000 >/proc/sys/fs/file-max)
* setting clock=pit kernel parameter
* setting rcupdate.maxbatch=1000000 kernel parameter

Is there some other way to make the kernel less sensitive to ill-behaved
hardware timers, as it was pre-2.6.14, assuming that I am willing to sacrifice
real-time performance?

Any help would be appreciated.


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