Keeping mmap'ed files in core regression in 2.6.7-rc

[Miquel van Smoorenburg <miquels@cistron.nl>]

I'm running a Usenet news server with a full feed. Software is
INN 2.4.1.

The list of all articles is called the "history database" and is
indexed by a history.hash and a history.index file, both sized
around 300-400 MB.

These hash and index files are mmap'ed by the main innd process.

A full usenet feed is 800-1000 GB/day, that's ~ 12MB / sec incoming
traffic going to the local spool disk. About the same amount of
traffic is sent out to peers.

With kernels 2.6.0 - 2.6.6, I did a "echo 15 > /proc/sys/vm/swappiness"
and the kernel did a pretty good job of keeping the mmap'ed files
mostly in core, which is needed for performance (100-200 database
queries/sec!).

This is the output with a 2.6.6 kernel:

# ps u -C innd
USER       PID %CPU %MEM   VSZ  RSS TTY      STAT START   TIME COMMAND
news       276 26.8 60.2 817228 624932 ?     D    01:57 232:55 /usr/local/news/b

Now I tried 2.6.7-rc2 and -rc3 (well rc2-bk-latest-before-rc3) and
with those kernels, performance goes to hell because no matter
how much I tune, the kernel will throw out the mmap'ed pages first.
RSS of the innd process hovers around 200-250 MB instead of 600.

Ideas ?

Mike.

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