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

[Peter Jeremy]

[CC list pruned]

On Thu, Jul 28, 2005 at 02:13:44PM -0700, Julian Elischer wrote:
>file data written to cache to await output to disk is allowed to grow to 
>the extent that running programs are swapped out.
>(or at least paged out).

I don't see this on 5.3 either.  In multi-user mode (with lots of
other processes sitting aroung idle) vmstat shows fr and sr sit at
around 10,000/sec but there's no paging and a "ps -axl" afterwards
shows everything mostly still resident.  The active memory (avm)
hardly changes but free memory drops from 233MB to 20MB over 8 seconds
than oscillates between about 16MB and 30MB.  Disk I/O remains at
35-40MB/sec (ie disk limited).

This is an Athlon XP-1800 512MB RAM writing a 10GB file onto an ATA disk.
PREEMPTION is enabled.

Since Marc Olzheim reports it happens with 5-STABLE and Julian reports
it doesn't happen on 5.4 and I can't reproduce it on 5.3, one option
would seem to be that it was MFC'd to 5 at some point since 5.4 was
branched.  Unfortunately, a quick scan through the RELENG_5 commits
doesn't reveal anything that might be relevant.

The other possibility is that it's RAM size related.  The vmstat
output Julian posted demonstrating the problem was on a system with a
fair bit of RAM, but his 5.4 system is presumably smaller and my
system definitely is.

-- 
Peter