6.0 VFS/VM over-runs. Was: Apparent strange disk behaviour in 6.0

[Marc Olzheim]

On Thu, Jul 28, 2005 at 02:13:44PM -0700, Julian Elischer wrote:
> mount a large partition  that has some room.. hopefully several times 
> the space of all RAM.
> .
> 
> do:
> 
> dd if=/dev/zero of=/${mountpoint}/bigfile bs=128k count=1000000 & iostat 1
> 
> 
> notice that dd dies with "not enough swapspace" after some number of 
> seconds.
> (there is no swap attached).  also notice that until the crash, IO speed 
> was max for the
> disk.
> 
> then add swap and do it again.
> 
> notice that at teh point where dd previously crashed, the swap disk
> springs into life and disk IO on your main disk goes into the toilet.
> notice that dd gets swapped out. (!!!!)
> 
> when the disk recovers enough, dd pages back in and creates more IO but 
> in teh mean time there is no IO
> going on to the disk.. (watch the LEDs).

Just to be clear, this happens on 5-STABLE, 6-STABLE and 7-CURRENT.

Marc
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