[SPARC32]: Reduce fragmentation in the bitmap allocator

The existing allocator is first-fit with wraparound.  This allows
a large number of small holes to accumulate in the early part of the
region, leading to heavy fragmentation.  This adjusts the algorithm
to rescan the region when smaller sizes are requested, reducing
early fragmentation.

arch/sparc/lib/bitext.c

@@ -42,7 +42,10 @@ int bit_map_string_get(struct bit_map *t, int len, int align)
 		BUG();
 
 	spin_lock(&t->lock);
-	offset = t->last_off & ~align1;
+	if (len < t->last_size)
+		offset = t->first_free;
+	else
+		offset = t->last_off & ~align1;
 	count = 0;
 	for (;;) {
 		off_new = find_next_zero_bit(t->map, t->size, offset);
@@ -71,9 +74,14 @@ int bit_map_string_get(struct bit_map *t, int len, int align)
 			if (i == len) {
 				for (i = 0; i < len; i++)
 					__set_bit(offset + i, t->map);
+				if (offset == t->first_free)
+					t->first_free = find_next_zero_bit
+							(t->map, t->size,
+							 t->first_free + len);
 				if ((t->last_off = offset + len) >= t->size)
 					t->last_off = 0;
 				t->used += len;
+				t->last_size = len;
 				spin_unlock(&t->lock);
 				return offset;
 			}
@@ -96,6 +104,8 @@ void bit_map_clear(struct bit_map *t, int offset, int len)
 			BUG();
 		__clear_bit(offset + i, t->map);
 	}
+	if (offset < t->first_free)
+		t->first_free = offset;
 	t->used -= len;
 	spin_unlock(&t->lock);
 }
@@ -111,4 +121,6 @@ void bit_map_init(struct bit_map *t, unsigned long *map, int size)
 	spin_lock_init(&t->lock);
 	t->map = map;
 	t->size = size;
+	t->last_size = 0;
+	t->first_free = 0;
 }

include/asm-sparc/bitext.h

@@ -15,6 +15,8 @@ struct bit_map {
 	int size;
 	int used;
 	int last_off;
+	int last_size;
+	int first_free;
 };
 
 extern int bit_map_string_get(struct bit_map *t, int len, int align);