more weird bugs with mmap-ing via NFS

[Mikhail Teterin]

> When I mount with large read and write sizes:
>
> 	mount_nfs -r 65536 -w 65536 -U -ointr pandora:/backup /backup
>
> it changes -- for the worse. Short time into it -- the file stops growing
> according to the `ls -sl' run on the NFS server (pandora) at exactly 3200
> FS blocks (the FS was created with `-b 65536 -f 8129').
>
> At the same time, according to `systat -if' on both client and server, the
> client continues to send (and the server continues to receive) about 30Mb
> of some (?) data per second.

When the client is in this state it remains quite usable except for the 
following:

	1) Trying to start `systat 1 -vm' stalls ALL access to local disks,
	   apparently -- no new programs can start, and the running ones
	   can not access any data either; attempts to Ctrl-C the starting
	   systat succeed only after several minutes.

	2) The writing process is stuck unkillable in the following state:

		CPU PRI NI   VSZ   RSS MWCHAN STAT  TT       TIME
		27  -4  0 1351368 137764 nfs    DL    p4    1:05,52

	   Sending it any signal has no effect. (Large sizes are explained
	   by it mmap-ing its large input and output.)

	3) Forceful umount of the share, that the program is writing to,
	   paralyzes the system for several minutes -- unlike in 1), not
	   even the mouse is moving. It would seem, the process is dumping
	   core, but it is not -- when the system unfreezes, the only
	   message from the kernel is:

		vm_fault: pager read error, pid XXXX (mzip)
	  
Again, this is on 6.1/i386 from today, which we are about to release into the 
cruel world.

Yours,

	-mi