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    SubjectWhere's all my memory going?
    Hi,

    I've fashioned a qmail mail server using an HP NetServer with an HP NetRaid
    4M & 1GB RAM, running 2.4.17 with aacraid, LVM, ext3 and highmem. The box
    has 6x 9GB disks, one for system, one for qmail's queue, and the remaining
    four are RAID5'd with LVM. ext3 is only on the queue disk, ext2 everywhere
    else.

    Before I stick the box live, I wanted to test that it doesn't fall over
    under any remote kind of stress, so I've run postal to simulate lots of mail
    connections.

    Nothing too hard to begin with, but I'm seeing a degradation in performance
    over time, using a maximum message size of 10KB, 5 simultaneous connections,
    and limiting to 1500 messages per minute.

    Initially the box memory situation is like this:

    root@plum:~# free
    total used free shared buffers cached
    Mem: 1029524 78948 950576 0 26636 23188
    -/+ buffers/cache: 29124 1000400
    Swap: 2097136 0 2097136

    ...running postal, it seems to cope fine. Checking the queue using
    qmail-qstat shows no messages being delayed for delivery, everything I chuck
    at it is being delivered straight away.

    However, over time, (30-45 minutes), more and more memory seems to just
    disappear from the system until it looks like this, (note that swap is
    hardly ever touched):

    root@plum:~# free
    total used free shared buffers cached
    Mem: 1029524 1018032 11492 0 49380 245568
    -/+ buffers/cache: 723084 306440
    Swap: 2097136 676 2096460

    ...and qmail-qstat reports a few thousand queued messages. Even if I stop
    the postal process, let the queue empty and start again, it never attains
    the same performance as it did initially and the queue gets slowly filled.

    I haven't left it long enough to see if the box grinds itself into the
    ground, but it appears to stay at pretty much the same level as above, once
    it gets there. CPU load stays at about ~5.0, (PIII 533), but it's still
    very reponsive to input and launching stuff.

    Looking at the processes, the biggest memory hog is a copy of dnscache that
    claims to have used ~10MB, which is fine as I specified a cache of that size.
    Nothing else shows any hint of excessive memory usage.

    Can anyone offer any advice or solution to this behaviour, (or more tricks
    or settings I can try)? I'd like the mail server to be able to handle 1500
    messages instead of 150 a minute! :-) Any extra info required, please let me
    know, I'm not sure what else to provide atm.

    Cheers

    Matt
    --
    "Phased plasma rifle in a forty-watt range?"
    "Hey, just what you see, pal"
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