Strange memory issue(?) with 6850

[Ben Scott]

On 3/2/07, Dominique.GARNIER at arval.fr <Dominique.GARNIER at arval.fr> wrote:
> If i sum all the process VSZ and RSS size that way i got:

  VSZ is "Virtual Size" -- the total size of all pages mapped into
that processes's virtual address space.  Some or even most of those
pages might not correspond to physical memory.  So VSZ has little to
nothing to do with actual RAM consumption.  Ignore it.

  RSS is Resident Set Size, which is more useful.  That's how much RAM
the process is currently using.

> 109Mo RSS on a problematic server
> 115Mo RSS on a server displaying around 8Go

  So, about the same.

  What is "problematic" about the first server?  Are you just looking
at the output of "free", or is there something more going on?

> This are the free outputs corresponding to the two servers ...

  Unfortunately, the output is getting scrambled in email, so I can't
line up which columns belong where.  But I suspect you're getting
tripped up by the fact that the kernel will use any available memory
for cache and buffers, and "free" reports that usage.  But as soon as
a process needed the memory for something else, the cache will be
released to the process.

  To make this clearer, look at the "-/+ buffers/cache" line in the
"free" output.  That line shows you free and used statistics, but with
buffers and cached considered "free" rather than "used".  (You also
might want to add the "-m" switch, which shows counts in megabytes,
which I find easier to read.)

  Take a look at this:

http://wiki.linuxquestions.org/wiki/Free_%28command%29

... in particular, the example output at the bottom.  The first
statistics line ("Mem:") would seem to indicate that out of 499 total
megabytes, 490 are used and only 9 are free.  However, the second
statistics line ("-/+ buffers/cache:") reveals that, if one considers
buffers and cache as free rather than used, only 281 megabytes are
used, and 218 megabytes are "free" (either completely unused, or as
buffers/cache that can be released immediately).

  Does that help?

-- Ben