dynamic_pager.c   [plain text]

/* File created by Chris Youngworth, Apple Computer 2/11/99 */


#define mig_external

#include <mach/port.h>
#include <mach/mach_error.h>
#include <mach/mach_traps.h>
#include <mach/mach.h>
#ifndef MACH_BSD
#define MACH_BSD
#endif
#include <mach/mach_syscalls.h>
#include <mach/mach_traps.h>
#include <mach/mig_errors.h>
#include <sys/param.h>
#include <sys/mount.h>
#include <sys/file.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <sys/sysctl.h>
#include <sys/gmon.h>
#include <sys/types.h>
#include <errno.h>
#include <limits.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <nlist.h>
#include <ctype.h>
#include <unistd.h> 
#include <paths.h>
#include <dirent.h>

#include <CoreFoundation/CoreFoundation.h>

#include <default_pager/default_pager_types.h>
#include <default_pager_alerts_server.h>
#include <backing_store_alerts.h>
#include <backing_store_triggers_server.h>

/*
 * HI_WATER_DEFAULT set to this funny value to 
 * match the size that the low space application
 * is asking for... need to keep MINIMUM_SIZE
 * above this value.
 */
#define HI_WATER_DEFAULT 40000000
#define MINIMUM_SIZE (1024 * 1024 * 64)
#define MAXIMUM_SIZE  (1024 * 1024 * 1024)

#define MAX_LIMITS 8

#if TARGET_OS_EMBEDDED

#include <System/sys/content_protection.h>

#define USE_SYSTEMCONFIGURATION_PRIVATE_HEADERS 1
#include <SystemConfiguration/SystemConfiguration.h>

enum {
	VM_PAGING_MODE_DISABLED = 0,
	VM_PAGING_MODE_FREEZE,
	VM_PAGING_MODE_DYNAMIC
};

#define VM_FREEZE_SYSCTL "vm.freeze_enabled"
#define FREEZE_FIXED_SWAP_SIZE (128 * 1024 * 1024)
#endif

struct limit {
        unsigned int size;
        unsigned int low_water;
} limits[MAX_LIMITS];


int	debug = 0;
int     max_valid  = 0;
int	file_count = 0;
unsigned int	hi_water;
unsigned int	local_hi_water;
int	priority = 0;
int	options  = 0;
char	fileroot[512];


/* global parameters for application notification option */
mach_port_t	trigger_port = MACH_PORT_NULL;
mach_port_t	notify_port = MACH_PORT_NULL;
unsigned int	notify_high = 0;
unsigned int	bs_recovery;

/*
void	setprof __P((struct kvmvars *kvp, int state));
void	dumpstate __P((struct kvmvars *kvp));
void	reset __P((struct kvmvars *kvp));
*/



mach_msg_return_t
server_alert_loop(
    mach_msg_size_t max_size,
    mach_port_t rcv_name,
    mach_msg_options_t options)
{
    mig_reply_error_t *bufRequest = 0, *bufReply = 0;
    register mach_msg_return_t mr;
    register kern_return_t kr;

    if ((kr = vm_allocate(mach_task_self(),
                     (vm_address_t *)&bufRequest,
                     max_size + MAX_TRAILER_SIZE,
                     TRUE)) != KERN_SUCCESS)
      return kr;
    mlock(bufRequest, max_size + MAX_TRAILER_SIZE);
    if ((kr = vm_allocate(mach_task_self(),
                     (vm_address_t *)&bufReply,
                     max_size + MAX_TRAILER_SIZE,
                     TRUE)) != KERN_SUCCESS)
      return kr;
    mlock(bufReply, max_size + MAX_TRAILER_SIZE);
    while(TRUE) {
       mr = mach_msg(&bufRequest->Head, MACH_RCV_MSG|options,
		     0, max_size, rcv_name,
		     MACH_MSG_TIMEOUT_NONE, MACH_PORT_NULL);
        if (mr == MACH_MSG_SUCCESS) {
           /* we have a request message */

           if(!(default_pager_alerts_server(
				&bufRequest->Head, &bufReply->Head)))
		backing_store_triggers_server(
				&bufRequest->Head, &bufReply->Head);

           if (!(bufReply->Head.msgh_bits & MACH_MSGH_BITS_COMPLEX) &&
               bufReply->RetCode != KERN_SUCCESS) {
               if (bufReply->RetCode == MIG_NO_REPLY)
                /*
                 * This return code is a little tricky--
                 * it appears that the demux routine found an
                 * error of some sort, but since that error
                 * would not normally get returned either to
                 * the local user or the remote one, we pretend it's
                 * ok.
                 */

               bufRequest->Head.msgh_remote_port = MACH_PORT_NULL;
               mach_msg_destroy(&bufRequest->Head);
	       continue;
           }

           if (bufReply->Head.msgh_remote_port == MACH_PORT_NULL) {
              /* no reply port, so destroy the reply */
              if (bufReply->Head.msgh_bits & MACH_MSGH_BITS_COMPLEX)
                  mach_msg_destroy(&bufReply->Head);
	   } else {
		break;
	   }
	} else {
	   break;
	}   
    } 

    (void)vm_deallocate(mach_task_self(),
                    (vm_address_t) bufRequest,
                    max_size + MAX_TRAILER_SIZE);
    (void)vm_deallocate(mach_task_self(),
                    (vm_address_t) bufReply,
                    max_size + MAX_TRAILER_SIZE);
    return KERN_FAILURE;

}       


kern_return_t
backing_store_triggers(dynamic_pager, hi_wat, flags, port)
 		mach_port_t	dynamic_pager;
		int		hi_wat;
		int		flags;
		mach_port_t 	port;
{
        int cur_limits;
	
	if (file_count > max_valid)
	        cur_limits = max_valid;
	else
	        cur_limits = file_count;

	if((hi_wat + limits[cur_limits].size) > limits[cur_limits].low_water) 
		return KERN_FAILURE; /* let ipc system clean up port */

	/* If there was a previous registration, throw it away */
	if (notify_port != MACH_PORT_NULL) {
		mach_port_deallocate(mach_task_self(), notify_port);
		notify_port = MACH_PORT_NULL;
	}

	notify_port = port;
	notify_high = hi_wat;
	if(hi_water < notify_high) {
		local_hi_water = notify_high;
	} else {
		local_hi_water = hi_water;
	}
	if(notify_high > hi_water) {
		default_pager_space_alert(trigger_port, HI_WAT_ALERT);
	}
	return KERN_SUCCESS;
}


kern_return_t
default_pager_space_alert(alert_port, flags)
	mach_port_t	alert_port;
	int	flags;
{
	char subfile[512];
	off_t	filesize;
	int	error=0, fd=0;
	kern_return_t	ret;
        int cur_limits;
	unsigned int cur_size;
	unsigned int notifications;

	
	if(flags & HI_WAT_ALERT) {

		file_count++;

		if (file_count > max_valid)
		        cur_limits = max_valid;
		else
		        cur_limits = file_count;

		cur_size = limits[cur_limits].size;
		filesize = cur_size;

		/*
		 * because the LO_WAT threshold changes relative to
		 * the size of the swap file we're creating
		 * we need to reset the LO_WAT_ALERT threshold each
		 * time we create a new swap file
		 */
		if (limits[cur_limits].low_water)
		        notifications = HI_WAT_ALERT | LO_WAT_ALERT;
		else
		        notifications = HI_WAT_ALERT;

		sprintf(subfile, "%s%d", fileroot, file_count);
		fd = open(subfile, O_CREAT|O_EXCL|O_RDWR,(mode_t)(S_IRUSR|S_IWUSR));
		if (fd == -1) {
			/* force error recovery below */
			error = -1;
		}	
#if TARGET_OS_EMBEDDED
		else {
			error = fcntl(fd, F_SETPROTECTIONCLASS, PROTECTION_CLASS_F);
		}
#endif
		
		if(!error) {	
			error = fcntl(fd, F_SETSIZE, &filesize);
			if(error) {
				error = ftruncate(fd, filesize);
			}
			if(error)
				unlink(subfile);
			close(fd);
		}

		if(error == -1) {
			file_count--;

			if (file_count > max_valid)
			        cur_limits = max_valid;
			else
			        cur_limits = file_count;

			if (limits[cur_limits].low_water)
			        notifications = HI_WAT_ALERT | LO_WAT_ALERT;
			else
			        notifications = HI_WAT_ALERT;
			
			notifications |= SWAP_FILE_CREATION_ERROR;

			local_hi_water = local_hi_water>>2;
			if(notify_high >= (local_hi_water)) {
				if(notify_port != MACH_PORT_NULL) {
					/* notify monitoring app of */
					/* backing store shortage  */
					backing_store_alert(notify_port,
								HI_WAT_ALERT);
					mach_port_deallocate(mach_task_self(), 
								notify_port);
					notify_port = MACH_PORT_NULL;
					notify_high = 0;
				}
			}
		} else {
			if(hi_water < notify_high) {
				if(local_hi_water < notify_high) {
				   bs_recovery = notify_high - local_hi_water;
				}
				local_hi_water = notify_high;
			} else {
				if(local_hi_water < hi_water) {
				   bs_recovery = hi_water - local_hi_water;
				}
				local_hi_water = hi_water;
			}
			ret = macx_swapon((uint64_t)(uintptr_t)subfile,
					  flags, cur_size, priority);

			if(ret) {
				unlink(subfile);
				file_count--;

				if (file_count > max_valid)
				        cur_limits = max_valid;
				else
				        cur_limits = file_count;

				if (limits[cur_limits].low_water)
				        notifications = HI_WAT_ALERT | LO_WAT_ALERT;
				else
				        notifications = HI_WAT_ALERT;

				local_hi_water = local_hi_water>>2;
				if(notify_high >= (local_hi_water)) {
					if(notify_port != MACH_PORT_NULL) {
						/* notify monitoring app of */
						/* backing store shortage  */
						backing_store_alert(
							notify_port,
							HI_WAT_ALERT);
						mach_port_deallocate(
							mach_task_self(), 
							notify_port);
						notify_port = MACH_PORT_NULL;
						notify_high = 0;
					}
				}
			} else if(bs_recovery <= cur_size) {
				if((bs_recovery != 0) && (notify_port)) {
					backing_store_alert(notify_port,
								LO_WAT_ALERT);
					mach_port_deallocate(mach_task_self(), 
								notify_port);
					notify_port = MACH_PORT_NULL;
					notify_high = 0;
					bs_recovery = 0;
				}
			} else 
				bs_recovery = bs_recovery-cur_size;
		}
		macx_triggers(local_hi_water, limits[cur_limits].low_water, notifications, alert_port);
	}
	if(flags & LO_WAT_ALERT) {
		sprintf(subfile, "%s%d", fileroot, file_count);
		if(hi_water < notify_high) {
			local_hi_water = notify_high;
		} else {
			local_hi_water = hi_water;
		}
		if((bs_recovery != 0) && (notify_port != MACH_PORT_NULL)) {
			backing_store_alert(notify_port, LO_WAT_ALERT);
			mach_port_deallocate(mach_task_self(), notify_port);
			notify_port = MACH_PORT_NULL;
			notify_high = 0;
			bs_recovery = 0;
		}
		if((error = macx_swapoff((uint64_t)(uintptr_t)subfile,
					 flags)) == 0) {

			unlink(subfile);
			file_count--;

			if (file_count > max_valid)
			        cur_limits = max_valid;
			else
			        cur_limits = file_count;
		} else {
			if (file_count > max_valid)
			        cur_limits = max_valid;
			else
			        cur_limits = file_count;
		}
		/*
		 * only need to reset the LO_WAT_ALERT... the HI_WAT size is fixed,
		 * it doesn't change even if the swap file size shrinks or grows
		 */
		macx_triggers(local_hi_water, limits[cur_limits].low_water, LO_WAT_ALERT, alert_port);
	}
	return KERN_SUCCESS;
}

void
wait_on_paging_trigger(trigger_port)
	mach_port_t	trigger_port;
{
	kern_return_t	result;
	result = server_alert_loop(4096, trigger_port, MACH_MSG_OPTION_NONE);
	if (result != KERN_SUCCESS) {
	     fprintf(stderr, "dynamic_pager: default pager alert failed\n");
	     exit(EXIT_FAILURE);
	}
	exit(EXIT_SUCCESS);
}

void
paging_setup(flags, size, priority, low, high, encrypted)
	int	flags;
	int	size;
	int	priority;
	int	low;
	int	high;
	boolean_t	encrypted;
{
	off_t		filesize = size;
	char 		subfile[512];
	int		error, fd = 0;

	file_count = 0;
	sprintf(subfile, "%s%d", fileroot, file_count);
	fd = open(subfile, O_CREAT|O_EXCL|O_RDWR, ((mode_t)(S_IRUSR|S_IWUSR)));
	if (fd == -1) {
		fprintf(stderr, "dynamic_pager: cannot create paging file %s!\n",
			subfile);
		exit(EXIT_FAILURE);
	}

#if TARGET_OS_EMBEDDED
	error = fcntl(fd, F_SETPROTECTIONCLASS, PROTECTION_CLASS_F);
	if (error == -1) {
		fprintf(stderr, "dynamic_pager: cannot set file protection class!\n");
		unlink(subfile);
		close(fd);
		exit(EXIT_FAILURE);
	}
#endif

	error = fcntl(fd, F_SETSIZE, &filesize);
	if(error) {
		error = ftruncate(fd, filesize);
	}
	close(fd);

	if (error == -1) {
		fprintf(stderr, "dynamic_pager: cannot extend paging file size %s to %llu!\n",
			subfile, filesize);
		exit(EXIT_FAILURE);
	}
        
	if (macx_triggers(0, 0,
			  (encrypted
			   ? SWAP_ENCRYPT_ON
			   : SWAP_ENCRYPT_OFF),
			  MACH_PORT_NULL) != 0) {
		fprintf(stderr,
			"dynamic_pager: warning: "
			"could not turn encrypted swap %s\n", 
			(encrypted ? "on" : "off"));
	}

	macx_swapon((uint64_t)(uintptr_t)subfile, flags, size, priority);

	if(hi_water) {
		mach_msg_type_name_t    poly;

		if (mach_port_allocate(mach_task_self(), 
				MACH_PORT_RIGHT_RECEIVE, 
				&trigger_port) != KERN_SUCCESS)  {
			fprintf(stderr,"dynamic_pager: allocation of trigger port failed\n");
			exit(EXIT_FAILURE);
		}
		/* create a send right on our local port */
		mach_port_extract_right(mach_task_self(), trigger_port,
			MACH_MSG_TYPE_MAKE_SEND, &trigger_port, &poly);
		macx_triggers(high, low, HI_WAT_ALERT, trigger_port);

		if(low) {
			macx_triggers(high, low, LO_WAT_ALERT, trigger_port);
		}
		/* register control port for applications wishing to */
		/* get backing store notifications or change dynamic */
		/* pager settings. */
		set_dp_control_port(mach_host_self(), trigger_port);
		wait_on_paging_trigger(trigger_port); 
	}
	exit(EXIT_SUCCESS);
}

static void
clean_swap_directory(const char *path)
{
	DIR *dir;
	struct dirent *entry;
	char buf[1024];

	dir = opendir(path);
	if (dir == NULL) {
		fprintf(stderr,"dynamic_pager: cannot open swap directory %s\n", path);
		exit(EXIT_FAILURE);
	}

	while ((entry = readdir(dir)) != NULL) {
		if (entry->d_namlen>= 4 && strncmp(entry->d_name, "swap", 4) == 0) {
			snprintf(buf, sizeof buf, "%s/%s", path, entry->d_name);
			unlink(buf);	
		}
	}

	closedir(dir);
}

#define VM_PREFS_PLIST				"/Library/Preferences/com.apple.virtualMemory.plist"
#define VM_PREFS_DISABLE_ENCRYPT_SWAP_KEY	"DisableEncryptedSwap"

static boolean_t
should_encrypt_swap(void)
{
	CFPropertyListRef 	propertyList;
	CFTypeID		propertyListType;	
	CFStringRef       	errorString;
	CFDataRef         	resourceData;
	SInt32            	errorCode;
	CFURLRef       		fileURL;
	CFTypeRef		disable_encrypted_swap;
	boolean_t		should_encrypt = TRUE;
	boolean_t		explicit_value = FALSE;

	fileURL = CFURLCreateFromFileSystemRepresentation(kCFAllocatorDefault, (const UInt8 *)VM_PREFS_PLIST, strlen(VM_PREFS_PLIST), false);
	if (fileURL == NULL) {
		/*fprintf(stderr, "%s: CFURLCreateFromFileSystemRepresentation(%s) failed\n", getprogname(), VM_PREFS_PLIST);*/
		goto done;
	}
	
	if (!CFURLCreateDataAndPropertiesFromResource(kCFAllocatorDefault, fileURL, &resourceData, NULL, NULL, &errorCode)) {
		/*fprintf(stderr, "%s: CFURLCreateDataAndPropertiesFromResource(%s) failed: %d\n", getprogname(), VM_PREFS_PLIST, (int)errorCode);*/
		CFRelease(fileURL);
		goto done;
	}
	
	CFRelease(fileURL);
	propertyList = CFPropertyListCreateFromXMLData(kCFAllocatorDefault, resourceData, kCFPropertyListMutableContainers, &errorString);
	if (propertyList == NULL) {
		/*fprintf(stderr, "%s: cannot get XML propertyList %s\n", getprogname(), VM_PREFS_PLIST);*/
		CFRelease(resourceData);
		goto done;
	}

	propertyListType = CFGetTypeID(propertyList);

	if (propertyListType == CFDictionaryGetTypeID()) {	
		disable_encrypted_swap = (CFTypeRef) CFDictionaryGetValue((CFDictionaryRef) propertyList, CFSTR(VM_PREFS_DISABLE_ENCRYPT_SWAP_KEY));
		if (disable_encrypted_swap == NULL) {
			/* no value: use the default value i.e. encrypted swap ON */
		} else if (CFGetTypeID(disable_encrypted_swap) != CFBooleanGetTypeID()) {
			fprintf(stderr, "%s: wrong type for key \"%s\"\n",
				getprogname(), VM_PREFS_DISABLE_ENCRYPT_SWAP_KEY);
			/* bogus value, assume it's "true" for safety's sake */
			should_encrypt = TRUE;
			explicit_value = TRUE;
		} else {
			should_encrypt = CFBooleanGetValue((CFBooleanRef)disable_encrypted_swap) ? FALSE : TRUE;
			explicit_value = TRUE;
		}
	}
	else {
		/*fprintf(stderr, "%s: invalid propertyList type %d (not a dictionary)\n", getprogname(), propertyListType);*/
	}
	CFRelease(resourceData);
	CFRelease(propertyList);

done:
	if (! explicit_value) {
#if TARGET_OS_EMBEDDED
		should_encrypt = FALSE;
#endif
	}

	return should_encrypt;
}

#if TARGET_OS_EMBEDDED

#define VM_PREFS_PAGING_MODE_PLIST	"com.apple.virtualMemoryMode.plist"
#define VM_PREFS_PAGING_MODE_KEY	"Mode"

static uint32_t
get_paging_mode(void)
{
	SCPreferencesRef paging_prefs;
	uint32_t paging_mode;
	
	paging_mode = VM_PAGING_MODE_FREEZE; /* default */
	
	paging_prefs = SCPreferencesCreate(NULL, CFSTR("dynamic_pager"), CFSTR(VM_PREFS_PAGING_MODE_PLIST));
	if (paging_prefs) {
		CFNumberRef value;

		value = SCPreferencesGetValue(paging_prefs, CFSTR(VM_PREFS_PAGING_MODE_KEY));
		
		if (value && (CFGetTypeID( value ) == CFNumberGetTypeID() ) ) {
			CFNumberGetValue((CFNumberRef)value, kCFNumberIntType, &paging_mode);
		} 

		CFRelease(paging_prefs);
	}
	
	return paging_mode;
}

#endif

int
main(int argc, char **argv)
{
	extern char *optarg;
	extern int optind;
	char default_filename[] = "/private/var/vm/swapfile";
	int ch;
	int variable_sized = 1,flags=0;
	boolean_t	encrypted_swap;
	static char tmp[1024];
	struct statfs sfs;
	char *q;
#if TARGET_OS_EMBEDDED
	int err;
	uint32_t paging_mode;
	size_t paging_mode_length;
#endif

/*
	setlinebuf(stdout);
	setlinebuf(stderr);
*/

	seteuid(getuid());
	strcpy(fileroot, default_filename);

retry:
	limits[0].size = 20000000;
	limits[0].low_water = 0;

	hi_water = 0;
	local_hi_water = 0;

	encrypted_swap = should_encrypt_swap();

	while ((ch = getopt(argc, argv, "EF:L:H:S:P:QO:")) != EOF) {
		switch((char)ch) {

		case 'E':
			encrypted_swap = TRUE;
			break;

		case 'F':
			strncpy(fileroot, optarg, 500);
			break;

		case 'L':
		        variable_sized = 0;
			limits[0].low_water = atoi(optarg);
			break;
		case 'H':
		        variable_sized = 0;
			hi_water = atoi(optarg);
			break;
		case 'S':
		        variable_sized = 0;
			limits[0].size = atoi(optarg);
			break;
		case 'P':
			priority = atoi(optarg);
			break;

		case 'Q':
			/* just query for "encrypted swap" default value */
			fprintf(stdout,
				"dynamic_pager: encrypted swap will be %s\n",
				encrypted_swap ? "ON": "OFF");
			exit(0);

		default:
			(void)fprintf(stderr,
			    "usage: dynamic_pager [-F filename] [-L low water alert trigger] [-H high water alert trigger] [-S file size] [-P priority]\n");
			exit(EXIT_FAILURE);
		}
	}

	/*
	 * get rid of the filename at the end of the swap file specification
	 * we only want the portion of the pathname that should already exist
	 */
	strcpy(tmp, fileroot);
	if ((q = strrchr(tmp, '/')))
	        *q = 0;

	/*
	 * Remove all files in the swap directory.
	 */
	clean_swap_directory(tmp);

#if TARGET_OS_EMBEDDED
	paging_mode = get_paging_mode();
	paging_mode_length = sizeof(paging_mode);
	
	switch (paging_mode) {
		case VM_PAGING_MODE_DISABLED:
			/* Paging disabled; nothing to do here so exit */
			exit(EXIT_SUCCESS);

		case VM_PAGING_MODE_FREEZE:
			/* Freeze mode; one swap file of fixed size, so enable and override defaults if set */
			err = sysctlbyname(VM_FREEZE_SYSCTL, NULL, 0, &paging_mode, paging_mode_length);
			if (err < 0) {
				(void)fprintf(stderr, "dynamic_pager: cannot set %s\n", VM_FREEZE_SYSCTL);
				exit(EXIT_FAILURE);
			}
			variable_sized = 0;
			limits[0].size = FREEZE_FIXED_SWAP_SIZE;
			break;

		case VM_PAGING_MODE_DYNAMIC:
			/* Dynamic paging selected; proceed normally */
			break;

		default:
			/* Invalid option */
			(void)fprintf(stderr, "dynamic_pager: invalid paging_mode %d\n", paging_mode); 
			exit(EXIT_FAILURE);
	}
#endif

	if (statfs(tmp, &sfs) == -1) {
	/*
	 * Setup the swap directory.
	 */
       	if (mkdir(tmp, 0755) == -1) {
		(void)fprintf(stderr, "dynamic_pager: cannot create swap directory %s\n", tmp); 
		exit(EXIT_FAILURE);
		}
	}
	chown(tmp, 0, 0);

	if (variable_sized) {
		int  i;
		int  mib[4];
		size_t len;
		unsigned int size;
		u_int64_t  memsize;
		u_int64_t  fs_limit = 0;

		/*
		 * if we get here, then none of the following options were specified... -L, H, or -S
		 * drop into a new mode that scales the size of the swap file based on how much free
		 * space is left on the volume being used for swap and the amount of physical ram 
		 * installed on the system...
		 * basically, we'll pick a maximum size that doesn't exceed the following limits...
		 *   1/8 the remaining free space of the swap volume 
		 *   the size of phsyical ram
		 *   MAXIMUM_SIZE - currently set to 1 Gbyte... 
		 * once we have the maximum, we'll create a list of sizes and low_water limits
		 * we'll start with 2 files of MINIMUM_SIZE - currently 64 Mbytes...
		 * subsequent entries will double in size up to the calculated maximum... the low_water
		 * limit will be the sum of the current file size and the previous file size for each entry...
		 * as we add or delete files, we'll use the current file_count as an index into this 
		 * table... if it's beyond the table size, we'll use the last entry
		 * the table entry will determine the size of the file to be created and the new low_water mark...
		 * the high_water mark is set to HI_WATER_DEFAULT which  must be smaller than MINIMUM_SIZE...
		 * currently it is set to 40,000,000 to match the size being requested by the application 
		 * monitoring low space conditions... having it set to the same size keeps us from creating
		 * an additional swap file when it really isn't necessary
		 */

		if (statfs(tmp, &sfs) == -1) {
			/*
			 * We really can't get filesystem status,
			 * so let's not limit the swap files...
			 */
			fs_limit = (u_int64_t) -1;
		}
		
		if (fs_limit != (u_int64_t) -1) {
			/*
			 * Limit the maximum size of a swap file to 1/8 the free
			 * space available on the filesystem where the swap files
			 * are to reside.  This will allow us to allocate and
			 * deallocate in finer increments on systems without much
			 * free space.
			 */
		        fs_limit = ((u_int64_t)sfs.f_bfree * (u_int64_t)sfs.f_bsize) / 8;
		}

		mib[0] = CTL_HW;
		mib[1] = HW_MEMSIZE;
		len = sizeof(u_int64_t);

		if (sysctl(mib, 2, &memsize, &len, NULL, 0) < 0) {
		        /*
			 * if the sysctl fails for some reason
			 * use the starting size as the default
			 */
		        memsize = MINIMUM_SIZE;
		}
		if (memsize > fs_limit)
		        /*
			 * clip based on filesystem space available
			 */
		        memsize = fs_limit;

		/*
		 * further limit the maximum size of a swap file
		 */
		if (memsize <= MINIMUM_SIZE) {
			(void)fprintf(stderr,  "dynamic_pager: Need more space on the disk to enable swapping.\n"); 
			sleep(30);
			goto retry;
		} else if (memsize <= (MINIMUM_SIZE*2)) {
			(void)fprintf(stderr,  "dynamic_pager: Activating emergency swap file immediately.\n"); 
			flags |= USE_EMERGENCY_SWAP_FILE_FIRST;
		} else if (memsize > MAXIMUM_SIZE) {
		        memsize = MAXIMUM_SIZE;
		} 
		
		size = MINIMUM_SIZE;

		/*
		 * start small and work our way up to the maximum
		 * sized allowed... this way, we don't tie up too
		 * much disk space if we never do any real paging
		 */
		for (max_valid = 0, i = 0; i < MAX_LIMITS; i++) {
		        limits[i].size = size;

			if (i == 0)
			        limits[i].low_water = size * 2;
			else {
			        if ((limits[i - 1].size / 2) > HI_WATER_DEFAULT)
				        limits[i].low_water = size + (limits[i - 1].size / 2);
				else
				        limits[i].low_water = size + limits[i - 1].size;
			}
			
			if (i) {
			        /*
				 * make the first 2 files the same size
				 */
			        size = size * 2;
				if (size > memsize)
					break;
			}
			max_valid++;
		}
		if (max_valid >= MAX_LIMITS)
		        max_valid = MAX_LIMITS - 1;

		hi_water = HI_WATER_DEFAULT;
	}
	local_hi_water = hi_water;

	if((limits[0].low_water != 0) && (limits[0].low_water <= (limits[0].size + hi_water))) {
		(void)fprintf(stderr,  "dynamic_pager: low water trigger must be larger than size + hi_water\n"); 
		exit(EXIT_FAILURE);
	}
	argc -= optind;
	argv += optind;

	paging_setup(flags, limits[0].size, priority, limits[0].low_water, hi_water,
		     encrypted_swap);

	return (0);
}