even though it's a lost cause, try a little harder to guess at the amout
of free memory on nix.  it's at least the free pages plus the unallocated
physical memory of any color

Reference: /n/atom/patch/applied/ventinixfreemem
Date: Thu Apr  3 18:25:17 CES 2014
Signed-off-by: quanstro@quanstro.net

--- /sys/src/cmd/venti/srv/venti.c	Thu Apr  3 18:25:12 2014
+++ /sys/src/cmd/venti/srv/venti.c	Thu Apr  3 18:25:13 2014
@@ -25,41 +25,91 @@
 
 static void	ventiserver(void*);
 
+static uvlong
+capmem(uvlong size)
+{
+	char buf[64], *s;
+	uvlong bos;
+	Biobuf *b;
+
+	/* don't run into the stack */
+	snprint(buf, sizeof buf, "/proc/%d/segment", getpid());
+	if((b = Bopen(buf, OREAD)) != nil){
+		for(; (s = Brdstr(b, '\n', 1)) != nil; free(s)){
+			if(strncmp(s, "Stack", 5) != 0)
+				continue;
+			bos = strtoull(s+10, 0, 16);
+			if(size >= bos){
+				fprint(2, "warning: memsize stack limited %lld\n", bos);
+				size = bos;
+			}
+		}
+		Bterm(b);
+	}
+
+	/* malloc is limited */
+//	if(sizeof(uintptr) < 8)
+	if (size >= 3840ull * 1024 * 1024)
+		size = 3840ull * 1024 * 1024;
+	return size;
+}
+
 static ulong
 freemem(void)
 {
 	int nf, pgsize = 0;
-	uvlong size, userpgs = 0, userused = 0;
+	uvlong size, n, userpgs = 0, userused = 0;
 	char *ln, *sl;
-	char *fields[2];
+	char *fields[10];
 	Biobuf *bp;
 
-	size = 64*1024*1024;
+	size = 0;
 	bp = Bopen("#c/swap", OREAD);
 	if (bp != nil) {
 		while ((ln = Brdline(bp, '\n')) != nil) {
 			ln[Blinelen(bp)-1] = '\0';
 			nf = tokenize(ln, fields, nelem(fields));
-			if (nf != 2)
-				continue;
-			if (strcmp(fields[1], "pagesize") == 0)
+			if (nf == 2 && strcmp(fields[1], "pagesize") == 0)
 				pgsize = atoi(fields[0]);
-			else if (strcmp(fields[1], "user") == 0) {
+			else if (nf == 2 && strcmp(fields[1], "user") == 0) {
 				sl = strchr(fields[0], '/');
 				if (sl == nil)
 					continue;
 				userpgs = atoll(sl+1);
 				userused = atoll(fields[0]);
 			}
+			else if (nf>2 && strcmp(fields[2], "user") == 0){
+				/* nix */
+				n = unittoull(fields[1]);
+				if(n == 0)
+					continue;
+				sl = strchr(fields[0], '/');
+				if (sl == nil)
+					continue;
+				if(0)fprint(2, "size += (%lld - %lld)*%lld\n", atoll(sl+1), atoll(fields[0]), n);
+				size += (atoll(sl+1) - atoll(fields[0]))*n;
+			}
+			else if(nf>2 && strcmp(fields[1], "blocks") == 0){
+				if(strcmp(fields[2], "avail") != 0)
+					continue;
+				/* nix: add in unpreallocated pages */
+				sl = strchr(fields[0], '/');
+				if (sl == nil)
+					continue;
+				n = unittoull(fields[3]);
+				if(n == 0)
+					continue;
+				if(0)fprint(2, "*size += %lld*%lld\n", atoll(sl+1), n);
+				size += atoll(sl+1)*n;
+			}
 		}
 		Bterm(bp);
-		if (pgsize > 0 && userpgs > 0 && userused > 0)
+		if (size == 0 && pgsize > 0 && userpgs > 0 && userused > 0)
 			size = (userpgs - userused) * pgsize;
 	}
-	/* cap it to keep the size within 32 bits */
-	if (size >= 3840UL * 1024 * 1024)
-		size = 3840UL * 1024 * 1024;
-	return size;
+	if(size == 0)
+		size = 64*1024*1024;
+	return capmem(size);
 }
 
 static void
@@ -97,8 +147,7 @@
 		fprint(2, "%s: bloom filter bigger than mem pcnt; "
 			"resorting to minimum values (9MB total)\n", argv0);
 	else {
-		if (avail >= 3840UL * 1024 * 1024)
-			avail = 3840UL * 1024 * 1024;	/* sanity */
+		avail = capmem(avail);
 		avail /= 2;
 		all.icmem = avail;
 		avail /= 3;
@@ -247,7 +296,7 @@
 		configfile = "venti.conf";
 
 	/* remember free memory before initventi & loadbloom, for auto-sizing */
-	stfree = freemem(); 	 
+	stfree = freemem();
 	fprint(2, "conf...");
 	if(initventi(configfile, &config) < 0)
 		sysfatal("can't init server: %r");