[RndTbl] linux not caching files very long

Trevor Cordes trevor at tecnopolis.ca
Tue Nov 20 13:06:37 CST 2012

On 2012-11-20 Gilbert E. Detillieux wrote:
> I wouldn't be so sure about that, unless you've really checked that 
> closely, and/or disabled most system services that might affect

I have tried to monitor things closely with top, especially sorted by
memory usage.  I'm doubtful it's a change in usage that is causing this
because I have such a big (5GB) usual buffer/cached/free area, and I
really am doing nothing during these tests that would chew through 5GB
of files or data.  For instance, my cached line in top stays roughly
the same.  That would mean that it would have to be 4GB+ of other files
being read to flush out the stuff I want cached.

I run a lot of services but I've disabled all "automatic" and "desktop"
stuff, for instance I run no desktop index program, or anything like

It used to be that the only thing that would "uncache" my files is
watching some videos that obviously can chew through a few GB cache

> This is rather out of date for the 3.x kernels, but here's a pretty
> good tuning guide for RHEL 6 systems (2.6 kernel)...
> https://access.redhat.com/knowledge/docs/en-US/Red_Hat_Enterprise_Linux/6/html-single/Performance_Tuning_Guide/index.html#id2929235

I'll check that out.  Most of the tunables haven't changed since 2.6

> Have you tried setting swappiness all the way to 100?  Did that have
> no effect?

I'll try that next.  The more I read about swappiness, the more I get
confused whether in my case I want it set closer to 0 or closer to
100.  I thought 100, but it really doesn't frame things in terms of

> Adding more RAM might be another option.  :)

Older box with ECC, and 8 is the max (I have 4 sticks of 2), I think,
but I will double-check as RAM has gotten so cheap.  However, if I'm
looking at a $200 RAM bill (I think I paid $500 for the existing 8GB?)
then I'd be more likely to use it as a chance to get a whole new
ECC box :-)

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