/*
 * Copyright 2004 Sun Microsystems, Inc. ALL RIGHTS RESERVED 
 * Use of this software is authorized pursuant to the terms of 
the 
 * license found at 
http://developers.sun.com/berkeley_license.html
 */

#include <stdlib.h>
#include <stdio.h>
#include <kstat.h>
#include <sys/sysinfo.h>
#include <unistd.h>

/*
 * By Greg Nakhimovsky, Sun MDE, March 2004.
 * Returns current free physical memory in kilobytes computed as
 * pagesize*(system_pages.freemem - system_pages.lotsfree)/1024.
 * Note that the retuned value may be negative, meaning that
 * paging to disk is either imminent or already occurring.
 */

int phys_mem_avail(void)
{
   static long pagesize=0;
   static kstat_ctl_t *kc;
   static kstat_t *sys_pagesp;
   static size_t lotsfree;
   kstat_named_t *kn;
   size_t freemem;

   if(pagesize == 0)
   {
     /* Get the constant values (pagesize and lotsfree) once */
     pagesize = sysconf(_SC_PAGESIZE);
     if((kc=kstat_open()) == 0)
       perror("kstat_open"),exit(1);
     if((sys_pagesp=kstat_lookup(kc, "unix", 0, "system_pages")) == 0)
       perror("kstat_lookup(system_pages)"),exit(1);
     if(kstat_read(kc, sys_pagesp, 0) == -1)
       perror("kstat_read(syspages)"),exit(1);
     if((kn=kstat_data_lookup(sys_pagesp, "lotsfree")) == 0)
       perror("kstat_data_lookup(lotsfree)"),exit(1);
     lotsfree = kn->value.ul;
   }

   if(kstat_read(kc, sys_pagesp, 0) == -1)
     perror("kstat_read(syspages)"),exit(1);
   if((kn=kstat_data_lookup(sys_pagesp, "freemem")) == 0)
     perror("kstat_data_lookup(freemem)"),exit(1);
   freemem = kn->value.ul;

   return pagesize/1024*(freemem-lotsfree);
}