[RndTbl] linux not caching files very long

[Gilbert E. Detillieux]

On 2012-11-20 13:06, Trevor Cordes wrote:
> 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
> that.
>
> 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
> quickly.

You might also be interested in this article...

http://www.admin-magazine.com/Articles/Tuning-Your-Filesystem-s-Cache/

Specifically, the part about the vmtouch command and the "-dl" 
(daemonize and lock) option.  It would allow you to lock your large 
file(s) into memory while you work on them, I think.  That way, other 
system activity won't evict your cached pages.

>> 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
> cache/buffers.

I think you'd want to go to 100, to encourage more swapping, which would 
have the side-effect of (hopefully) leaving more memory available for 
disk caching.

-- 
Gilbert E. Detillieux		E-mail: <gedetil at muug.mb.ca>
Manitoba UNIX User Group	Web:	http://www.muug.mb.ca/
PO Box 130 St-Boniface		Phone:  (204)474-8161
Winnipeg MB CANADA  R2H 3B4	Fax:    (204)474-7609