On Fri, 2010-10-15 at 16:20 -0700, Tom Rushworth wrote:
> Hi Ken,
> 
> I'm no "ps" expert, but isn't the resident set size the wrong thing to
> be looking at?  My understanding is that rss is the amount of physical
> (real) memory currently paged in (resident) for a process, and that
> will go up and down as the system load changes.  If I understand
> correctly, you should be looking at something like vsize.  I'm also
> not running on Linux at the moment, but if I do a "man ps" on my Mac,
> it gives me the command option for adding fields to the output (in
> this case "-O") and a list of keywords (with short description) for
> things to add.  That would mean the the right  number to look at would
> be in the "vsz" column of the command "ps -O vsize".  The linux
> equivalent must surely exist for ps, and possibly for top as well.
> 
> Mind you, the VSZ numbers on my machine don't make a lot of sense to
> me, but they might on your linux box.  (The Mac man page says the VSZ
> is in Kbytes, but the numbers I actually get are ridiculous:
> 
> @ ps -O vsize
>   PID      VSZ   TT  STAT      TIME COMMAND
>   873  2435468 s000  S      0:00.03 -bash
>  1845   600772 s000  S+     0:01.53 /usr/local/bin/vile Shared/main.m
> .....
> I'm not too sure I believe 600Mbytes for a simple vi-like edit of a 20
> line file:).)

No I'm afraid not, and in fact you can see the problem here.  Processes
often request more memory than they actually use and Squeak is a prime
example here as, by default on Linux, it requests (mmaps I think) a full
gigabyte of RAM, which is more or less what you always see for VSZ for
squeak process, that doesn't mean it is actually using this, just that
it has requested a map with theoretically that much space.  The VSZ
value gives no useful information for my purposes.  I agree that RSS is
not ideal either, but it's closer than VSZ and I can clearly see that as
RSS goes up the free space reported by free goes down.  So in some sense
it is a a relevant figure to me since we tend to have very little free
RAM these days on the server and we are well into swap.

Ken
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