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

Julian Elischer julian at elischer.org
Fri Jul 29 19:40:33 GMT 2005



Marc Olzheim wrote:

>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.
>  
>

it doesn't appear to hit 5.4. at least not for my small ATA based 
workstation.

>Marc
>  
>


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