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SubjectRe: [VM] 2.4.14/15-pre4 too "swap-happy"?

On Wed, 14 Nov 2001, Sebastian Dröge wrote:
> The system has 256 MB RAM, nothing RAM-eating in the background I got many
> buffer-underuns just because of swapping. When I turn swap off everything
> works fine. I think it's something with the cache.

Can you do some statistics for me:

cat /proc/meminfo
cat /proc/slabinfo
vmstat 1

while the worst swapping is going on..

> Leaving system 2 alone, just play mp3s over nfs:
> After two or three days the used swap-space is around 3 MB. I just played
> MP3s and no X and no other "big" applications were running. This isn't really
> a problem but it doesn't look good. Just because of cache swap gets full :(

That's normal and usually good. It's supposed to swap stuff out if it
really isn't needed, and that improves performance. Cache _is_ more
important than swap if the cache is active.

HOWEVER, there's probably something in your system that triggers this too
easily. Heavy NFS usage will do that, for example - as mentioned in
another thread on linux-kernel, the VM doesn't really understand
writebacks and asynchronous reads from filesystems that don't use buffers,
and so sometimes the heuristics get confused simply because NFS activity
can _look_ like page mapping to the VM.

Your MP3-over-NFS doesn't sound bad, though. 3MB of swap is perfectly
normal: that tends to be just the idle deamons etc which really _should_
go to swapspace.

The cdrecord thing is something else, though. I'd love to see the
statistics from that. Although it can, of course, just be another SCSI
allocation strangeness.


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