Inexplicable disk activity trying to load modules on devfs

Daniel Jacobowitz (drow@false.org)
Sat, 15 Jun 2002 17:22:44 -0500

I just booted into 2.4.19-pre10-ac2 for the first time, and noticed
something very odd: my disk activity light was flashing at about
half-second intervals, very regularly, and I could hear the disk
moving. I was only able to track it down to which disk controller, via
/proc/interrupts (are there any tools for monitoring VFS activity?
They'd be really useful). Eventually I hunted down the program causing
it: xmms.

The reason turned out to be that I hadn't remembered to build my sound
driver for this kernel version. Every half-second xmms tried to open
/dev/mixer (and failed, ENOENT). Every time it did that there was
actual disk activity. Easily reproducible without xmms. Reproducible
on any non-existant device in devfs, but not for nonexisting files on
other filesystems. Is something bypassing the normal disk cache
mechanisms here? That doesn't seem right at all.

-- 
Daniel Jacobowitz                           Debian GNU/Linux Developer
MontaVista Software                         Carnegie Mellon University
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