Free memory pages estimation for process use

[Nicolas Joly <njoly%pasteur.fr@localhost>]

Hi,

While testing free memory consumable requests with OGS (Open Grid
Scheduler), i noticed that free memory reported by a NetBSD host was
amazingly low ... preventing its use.

By example, on a 8GB NetBSD/amd64 machine running -current :

njoly@lanfeust [gridscheduler/source]> qhost 
HOSTNAME                ARCH         NCPU  LOAD  MEMTOT  MEMUSE  SWAPTO  SWAPUS
-------------------------------------------------------------------------------
lanfeust.sis.pasteur.fr nbsd-x86_64     8  0.09    7.8G    7.7G   40.0G     0.0

At the same time 'vmstat -s'report the following:

     4096 bytes per page
        8 page colors
  2032144 pages managed
    10496 pages free
  1247833 pages active
   616160 pages inactive
        0 pages paging
     1510 pages wired
     8937 zero pages
        1 reserve pagedaemon pages
       40 reserve kernel pages
    10717 anonymous pages
  1848644 cached file pages
     6142 cached executable pages
[...]

Looking into the OGS code i found that memory/swap values are fetched
with VM_UVMEXP2 sysctl :

  mib[0] = CTL_VM;
  mib[1] = SGE_VM_UVMEXP;
  size   = sizeof(uvmexp);

  sysctl(mib, sizeof(mib)/sizeof(int), &uvmexp, &size, NULL, 0);

  /* Memory */
  mem_info->mem_total = ((double) uvmexp.npages * uvmexp.pagesize) / (1024 * 
1024);
  mem_info->mem_free  = ((double) uvmexp.free   * uvmexp.pagesize) / (1024 * 
1024);

  /* Swap */
  mem_info->swap_total = ((double) uvmexp.swpages * uvmexp.pagesize) / (1024 * 
1024);
  mem_info->swap_free = (((double) uvmexp.swpages - uvmexp.swpginuse) * 
uvmexp.pagesize) / (1024 * 1024);

But mem_free does only take uvmexp.free member into account, which
seems wrong to me. At least uvmexp.inactive should be added ...

Is it correct ? Anything else i missed ?

Thanks in advance,
Regards.

-- 
Nicolas Joly

Biology IT Center
Institut Pasteur, Paris.