[NBLUG/talk] My new debin server

[Chris Palmer]

Walter Hansen writes:

> After a fresh boot I generally get 1.6gigs out of 2 free, but it's
> been working hard and I've only got 137megs free. Should I be
> concerned? I'll include a cut from top.

No, you should not be concerned merely about memory utilization.  Free
RAM is money wasted.

Linux is very aggressive about cacheing flesystem reads and buffering
filesystem writes, to (greatly) improve performance.  If you're using
nearly 2GB, that means that Linux has cached/buffered 2GB minus total
applications size of files.  That means reads, writes and stats of those
files will be zoomy.

Linux will even swap out old, unused pages of application code and/or
data to make room for more filesystem cacheing/buffering!  So the (say)
1MB of startup code that is only used once for some application will be
retired, making more room for files.

The real measurement you want to look for is page-ins and page-outs.
These are the operations Linux does when it is actually swapping program
code or data in or out, and these are the real indicators of memory
starvation.  To see them, use vmstat(8):

$ vmstat 5
procs -----------memory---------- ---swap-- -----io---- --system-- ----cpu----
 r  b   swpd   free   buff  cache   si   so    bi    bo   in    cs us sy id wa
 1  0  26400   7280 102060 222228    0    0     3     4    6     3  1  0 99  0
 0  0  26400   7264 102060 222228    0    0     0     0  104    59  0  0 100  0
 0  0  26400   7224 102068 222260    0    0     0    69  121    81  0  0 100  0
 0  0  26400   7224 102068 222260    0    0     0    14  101    45  0  0 100  0
 0  0  26400   7208 102072 222272    0    0     0    51  110    73  0  0 100  0
 0  0  26400   7208 102072 222272    0    0     0     0  101    46  0  0 100  0

Look under the "swap" column for paging (si = "swap in", so = "swap
out").  This display also shows just how much RAM is used for buffering
writes and cacheing reads.  In my case, tons!  And that is how it should
be.


-- 
https://www.eff.org/about/staff/#chris_palmer

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