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Date:      Wed, 18 Feb 1998 05:03:34 -0800
From:      Mike Smith <mike@smith.net.au>
To:        hackers@FreeBSD.ORG
Subject:   Current kernel failure under heavy swap load
Message-ID:  <199802181303.FAA02700@dingo.cdrom.com>

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Some users of both -current and -stable have been reporting kernel 
failures under heavy load.  This message characterises this problem, 
offers a short-term workaround, and solicits input from the community 
to develop a solution.


The kernel failure is characterised by a fatal kernel trap (12) in 
the wfdstrategy() function.  The trap occurs regardless of whether a 
'wfd' device is in use or not.  It is possible for this failure to 
silently corrupt data on a mounted 'wfd' disk instead.

wfdstrategy() is called because the 'wfd' block device major number 
(1) is shared with the vm subsystem internal device 'sw'.

In order to avoid this failure, users should remove the 'wfd' driver 
from their kernel configuration until the issue is resolved.

Background:  The 'wfd' driver was recently assigned major 1 in an 
attempt to minimise the extra bulk required in the bootblocks to 
support booting from ATAPI removable disks (LS-120, Iomega Zip).  The 
'sw' pseudo-device is provided as a convenient mechanism for accessing 
the swstrategy() routine from within the vm system.

-- 
\\  Sometimes you're ahead,       \\  Mike Smith
\\  sometimes you're behind.      \\  mike@smith.net.au
\\  The race is long, and in the  \\  msmith@freebsd.org
\\  end it's only with yourself.  \\  msmith@cdrom.com



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