free: support for MemAvailable

This commit adds a new switch -a/--available that
appends a new column called 'available' to the
output. The column displays an estimation
of how much memory is available for starting
new applications, without swapping. Unlike the data
provided by the 'cached' or 'free' fields, this
field takes into account page cache and also that
not all reclaimable memory slabs will be reclaimed
due to items being in use.

free.1

@@ -33,6 +33,14 @@ Memory used by kernel buffers (Buffers in /proc/meminfo)
 .TP
 \fBcached\fR
 Memory used by the page cache (Cached in /proc/meminfo)
+.TP
+\fBavailable\fR
+Estimation of how much memory is available for starting
+new applications, without swapping. Unlike the data
+provided by the \fBcached\fR or \fBfree\fR fields,
+this field takes into account page cache and also that
+not all reclaimable memory slabs will be reclaimed
+due to items being in use (MemAvailable in /proc/meminfo)
 .SH OPTIONS
 .TP
 \fB\-b\fR, \fB\-\-bytes\fR
@@ -65,6 +73,10 @@ display the units of print out.  Following units are used.
 If unit is missing, and you have petabyte of RAM or swap, the number is in
 terabytes and columns might not be aligned with header.
 .TP
+\fB\-a\fR, \fB\-\-available\fR
+Display the estimation of memory available for starting new applications,
+without swapping. This switch makes the output wider than 80 characters.
+.TP
 \fB\-c\fR, \fB\-\-count\fR \fIcount\fR
 Display the result
 .I count

free.c

@@ -54,6 +54,7 @@
 #define FREE_SI			(1 << 5)
 #define FREE_REPEAT		(1 << 6)
 #define FREE_REPEATCOUNT	(1 << 7)
+#define FREE_AVAILABLE		(1 << 8)
 
 struct commandline_arguments {
 	int exponent;		/* demanded in kilos, magas... */
@@ -85,6 +86,7 @@ static void __attribute__ ((__noreturn__))
 	fputs(_(" -t, --total         show total for RAM + swap\n"), out);
 	fputs(_(" -s N, --seconds N   repeat printing every N seconds\n"), out);
 	fputs(_(" -c N, --count N     repeat printing N times, then exit\n"), out);
+	fputs(_(" -a, --available     show available memory\n"), out);
 	fputs(USAGE_SEPARATOR, out);
 	fputs(_("     --help     display this help and exit\n"), out);
 	fputs(USAGE_VERSION, out);
@@ -213,6 +215,7 @@ int main(int argc, char **argv)
 		{  "total",	no_argument,	    NULL,  't'		},
 		{  "seconds",	required_argument,  NULL,  's'		},
 		{  "count",	required_argument,  NULL,  'c'		},
+		{  "available",	no_argument,	    NULL,  'a'		},
 		{  "help",	no_argument,	    NULL,  HELP_OPTION	},
 		{  "version",	no_argument,	    NULL,  'V'		},
 		{  NULL,	0,		    NULL,  0		}
@@ -231,7 +234,7 @@ int main(int argc, char **argv)
 	textdomain(PACKAGE);
 	atexit(close_stdout);
 
-	while ((c = getopt_long(argc, argv, "bkmghlotc:s:V", longopts, NULL)) != -1)
+	while ((c = getopt_long(argc, argv, "bkmghlotc:as:V", longopts, NULL)) != -1)
 		switch (c) {
 		case 'b':
 			args.exponent = 1;
@@ -281,6 +284,9 @@ int main(int argc, char **argv)
 			  error(EXIT_FAILURE, ERANGE,
 				  _("failed to parse count argument: '%s'"), optarg);
 			break;
+		case 'a':
+			flags |= FREE_AVAILABLE;
+			break;
 		case HELP_OPTION:
 			usage(stdout);
 		case 'V':
@@ -296,7 +302,9 @@ int main(int argc, char **argv)
 		/* Translation Hint: You can use 9 character words in
 		 * the header, and the words need to be right align to
 		 * beginning of a number. */
-		printf("%s\n", _("             total       used       free     shared    buffers     cached"));
+		printf(_("             total       used       free     shared    buffers     cached"));
+		if (flags & FREE_AVAILABLE) printf(_("  available"));
+		printf("\n");
 		printf("%-7s", _("Mem:"));
 		printf(" %10s", scale_size(kb_main_total, flags, args));
 		printf(" %10s", scale_size(kb_main_used, flags, args));
@@ -304,6 +312,7 @@ int main(int argc, char **argv)
 		printf(" %10s", scale_size(kb_main_shared, flags, args));
 		printf(" %10s", scale_size(kb_main_buffers, flags, args));
 		printf(" %10s", scale_size(kb_main_cached, flags, args));
+		if (flags & FREE_AVAILABLE) printf(" %10s", scale_size(kb_main_available, flags, args));
 		printf("\n");
 		/*
 		 * Print low vs. high information, if the user requested it.

proc/libprocps.sym

@@ -26,6 +26,7 @@ global:
 	kb_inactive;
 	kb_low_free;
 	kb_low_total;
+	kb_main_available;
 	kb_main_buffers;
 	kb_main_cached;
 	kb_main_free;

proc/sysinfo.c

@@ -573,6 +573,7 @@ unsigned long kb_high_free;
 unsigned long kb_high_total;
 unsigned long kb_low_free;
 unsigned long kb_low_total;
+unsigned long kb_main_available;
 /* 2.4.xx era */
 unsigned long kb_active;
 unsigned long kb_inact_laundry;
@@ -629,6 +630,7 @@ void meminfo(void){
   {"LowFree",      &kb_low_free},
   {"LowTotal",     &kb_low_total},
   {"Mapped",       &kb_mapped},       // kB version of vmstat nr_mapped
+  {"MemAvailable", &kb_main_available}, // important
   {"MemFree",      &kb_main_free},    // important
   {"MemTotal",     &kb_main_total},   // important
   {"NFS_Unstable", &kb_nfs_unstable},

proc/sysinfo.h

@@ -34,6 +34,7 @@ extern unsigned long kb_high_free;
 extern unsigned long kb_high_total;
 extern unsigned long kb_low_free;
 extern unsigned long kb_low_total;
+extern unsigned long kb_main_available;
 /* 2.4.xx era */
 extern unsigned long kb_active;
 extern unsigned long kb_inact_laundry;  // grrr...