memory usage on Scyld slave nodes (fwd)

[Jag]

On Fri, 16 Feb 2001, Jag wrote:

> On Fri, 16 Feb 2001, Rick Niles wrote:
> 
> > 
> > > It works fine, but when I use BeoStatus to look at the slaves it
> > > shows that the slaves all have about 400MB of their memory taken up.
> > > Anyone know what is eating up the RAM on those slaves?  Each node
> > > has a total of 512MB of RAM.  Why is beowulf eating up so much of
> > > it?  Thanks.
> > 
> > I'm adding up all the memory that's in use on the entire machine, include
> > buffer cache for the filesystem.  Linux tries to use any spare memory up
> > to about 90% of available as a cache of the filesystem.
> > 
> > I realize that this make that value in beostatus pretty much
> > worthless.  It's also been pointed out that it's also the more
> > expensive for the kernel to compute.  I believe "top" actually walks
> > though the proc table and adds up all the memory to get it's value,
> > but that also seems a bit expensive to me.
> > 
> > So short answer, it's not a problem, it's just not a real useful number
> > and I'll still deciding how to make it better.
> 
> When you run the 'free' command, the first few numbers it shows seems to
> be similar to what beostatus shows.  What would probablly be a lot more
> useful would be the numbers from the seconds line, with the buffer/cache
> usage subtracted from to total used.  I haven't yet looked to see how
> expensive that computation is, but I think this number would be a lot
> more useful to show as I know the kernel will generally make total usage
> near 90%

I glanced at the code for both free and top (they're actually part of
the same package), and both of them pull memory information from
/proc/meminfo, the same place that libbeostat (and thus beostatus) pull
from.  Attached is a small patch that impliments my suggested change in
the way beostatus shows the information.


Jag
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diff -ur beostatus-2.0.8.orig/beostatus.c beostatus-2.0.8/beostatus.c
--- beostatus-2.0.8.orig/beostatus.c	Fri Jan  5 08:37:07 2001
+++ beostatus-2.0.8/beostatus.c	Fri Feb 16 22:31:07 2001
@@ -165,7 +165,7 @@
     exit (EXIT_FAILURE);
 
   status->mem.max = (double)(meminfo.mem.used + meminfo.mem.free)/1024.0/1024.0;
-  status->mem.curr = (double) meminfo.mem.used / 1024.0 / 1024.0;
+  status->mem.curr = (double) (meminfo.mem.used - meminfo.buffers - meminfo.cached) / 1024.0 / 1024.0;
   status->mem.unit = "MB";
 
   status->swap.max = (double)(meminfo.swap.used + meminfo.swap.free) / 1024.0 / 1024.0;
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