--- sys/dev/syscons/syscons.h.orig	2010-03-02 03:56:55.000000000 +0200
+++ sys/dev/syscons/syscons.h	2010-07-04 00:43:11.366661343 +0300
@@ -572,6 +572,7 @@
 
 /* schistory.c */
 #ifndef SC_NO_HISTORY
+void		sc_init_history(void);
 int		sc_alloc_history_buffer(scr_stat *scp, int lines,
 					int prev_ysize, int wait);
 void		sc_free_history_buffer(scr_stat *scp, int prev_ysize);
--- sys/dev/syscons/syscons.c.orig	2010-03-31 18:39:46.000000000 +0300
+++ sys/dev/syscons/syscons.c	2010-07-04 00:43:11.368678117 +0300
@@ -2726,8 +2726,12 @@
     int i;
 
     /* one time initialization */
-    if (init_done == COLD)
+    if (init_done == COLD) {
 	sc_get_bios_values(&bios_value);
+#ifndef SC_NO_HISTORY
+	sc_init_history();
+#endif
+    }
     init_done = WARM;
 
     /*
--- sys/dev/syscons/schistory.c.orig	2009-08-03 11:13:06.000000000 +0300
+++ sys/dev/syscons/schistory.c	2010-07-04 00:43:11.369673234 +0300
@@ -41,6 +41,7 @@
 #include <sys/tty.h>
 #include <sys/kernel.h>
 #include <sys/malloc.h>
+#include <sys/sysctl.h>
 
 #if defined(__sparc64__) || defined(__powerpc__)
 #include <machine/sc_machdep.h>
@@ -77,17 +78,37 @@
 static int		extra_history_size
 				= SC_MAX_HISTORY_SIZE - SC_HISTORY_SIZE*MAXCONS;
 
+static int		sc_history_size = SC_HISTORY_SIZE;
+
+SYSCTL_DECL(_hw_syscons);
+SYSCTL_INT(_hw_syscons, OID_AUTO, history_size, CTLFLAG_RDTUN, &sc_history_size, 0,
+    "Number of history buffer lines");
+
 /* local functions */
 static void copy_history(sc_vtb_t *from, sc_vtb_t *to);
 static void history_to_screen(scr_stat *scp);
 
+/* tune history buffer size */
+void
+sc_init_history(void)
+{
+
+	TUNABLE_INT_FETCH("hw.syscons.history_size", &sc_history_size);
+	if (sc_history_size < ROW * 4)
+	    sc_history_size = ROW * 4;
+	extra_history_size =
+	    ((sc_history_size * MAXCONS * MAXSC) > SC_MAX_HISTORY_SIZE ?
+		sc_history_size * MAXCONS * MAXSC : SC_MAX_HISTORY_SIZE) -
+		    sc_history_size * MAXCONS;
+}
+
 /* allocate a history buffer */
 int
 sc_alloc_history_buffer(scr_stat *scp, int lines, int prev_ysize, int wait)
 {
 	/*
 	 * syscons unconditionally allocates buffers upto 
-	 * SC_HISTORY_SIZE lines or scp->ysize lines, whichever 
+	 * sc_history_size lines or scp->ysize lines, whichever 
 	 * is larger. A value greater than that is allowed, 
 	 * subject to extra_history_size.
 	 */
@@ -98,7 +119,7 @@
 	int delta;				/* lines to put back */
 
 	if (lines <= 0)
-		lines = SC_HISTORY_SIZE;	/* use the default value */
+		lines = sc_history_size;	/* use the default value */
 
 	/* make it at least as large as the screen size */
 	lines = imax(lines, scp->ysize);
@@ -111,13 +132,13 @@
 	delta = 0;
 	if (prev_history) {
 		cur_lines = sc_vtb_rows(history);
-		min_lines = imax(SC_HISTORY_SIZE, prev_ysize);
+		min_lines = imax(sc_history_size, prev_ysize);
 		if (cur_lines > min_lines)
 			delta = cur_lines - min_lines;
 	}
 
 	/* lines upto min_lines are always allowed. */
-	min_lines = imax(SC_HISTORY_SIZE, scp->ysize);
+	min_lines = imax(sc_history_size, scp->ysize);
 	if (lines > min_lines) {
 		if (lines - min_lines > extra_history_size + delta) {
 			/* too many lines are requested */
@@ -196,7 +217,7 @@
 		return;
 
 	cur_lines = sc_vtb_rows(history);
-	min_lines = imax(SC_HISTORY_SIZE, prev_ysize);
+	min_lines = imax(sc_history_size, prev_ysize);
 	extra_history_size += (cur_lines > min_lines) ? 
 				  cur_lines - min_lines : 0;
 
--- share/man/man4/syscons.4.orig	2010-03-10 11:38:03.828597000 +0200
+++ share/man/man4/syscons.4	2010-07-04 18:41:03.496277934 +0300
@@ -442,6 +442,20 @@
 for a keyboard device if it is not currently attached to one.
 Otherwise, the driver only probes for a keyboard once during bootup.
 .El
+.Ss Loader Tunables
+Tunables can be set at the
+.Xr loader 8
+prompt before booting the kernel or stored in
+.Pa /boot/loader.conf .
+Some of these tunables also have a matching
+.Xr sysctl 8
+entry for access after boot.
+.Bl -tag -width indent
+.It hw.syscons.history_size
+Override the size of back scroll buffer (specified by the
+.Dv SC_HISTORY_SIZE
+option).
+.El
 .Sh FILES
 .Bl -tag -width /usr/share/syscons/xxxxyyyyzzz -compact
 .It Pa /dev/console