diff --git a/shallow.c b/shallow.c
index 4d0b005d39..11f7dde9d9 100644
--- a/shallow.c
+++ b/shallow.c
@@ -431,12 +431,14 @@ void remove_nonexistent_theirs_shallow(struct shallow_info *info)
 
 define_commit_slab(ref_bitmap, uint32_t *);
 
+#define POOL_SIZE (512 * 1024)
+
 struct paint_info {
 	struct ref_bitmap ref_bitmap;
 	unsigned nr_bits;
-	char **slab;
+	char **pools;
 	char *free, *end;
-	unsigned slab_count;
+	unsigned pool_count;
 };
 
 static uint32_t *paint_alloc(struct paint_info *info)
@@ -444,12 +446,15 @@ static uint32_t *paint_alloc(struct paint_info *info)
 	unsigned nr = (info->nr_bits + 31) / 32;
 	unsigned size = nr * sizeof(uint32_t);
 	void *p;
-	if (!info->slab_count || info->free + size > info->end) {
-		info->slab_count++;
-		REALLOC_ARRAY(info->slab, info->slab_count);
-		info->free = xmalloc(COMMIT_SLAB_SIZE);
-		info->slab[info->slab_count - 1] = info->free;
-		info->end = info->free + COMMIT_SLAB_SIZE;
+	if (!info->pool_count || size > info->end - info->free) {
+		if (size > POOL_SIZE)
+			die("BUG: pool size too small for %d in paint_alloc()",
+			    size);
+		info->pool_count++;
+		REALLOC_ARRAY(info->pools, info->pool_count);
+		info->free = xmalloc(POOL_SIZE);
+		info->pools[info->pool_count - 1] = info->free;
+		info->end = info->free + POOL_SIZE;
 	}
 	p = info->free;
 	info->free += size;
@@ -462,7 +467,7 @@ static uint32_t *paint_alloc(struct paint_info *info)
  * all walked commits.
  */
 static void paint_down(struct paint_info *info, const unsigned char *sha1,
-		       int id)
+		       unsigned int id)
 {
 	unsigned int i, nr;
 	struct commit_list *head = NULL;
@@ -474,7 +479,7 @@ static void paint_down(struct paint_info *info, const unsigned char *sha1,
 	if (!c)
 		return;
 	memset(bitmap, 0, bitmap_size);
-	bitmap[id / 32] |= (1 << (id % 32));
+	bitmap[id / 32] |= (1U << (id % 32));
 	commit_list_insert(c, &head);
 	while (head) {
 		struct commit_list *p;
@@ -507,12 +512,8 @@ static void paint_down(struct paint_info *info, const unsigned char *sha1,
 			    oid_to_hex(&c->object.oid));
 
 		for (p = c->parents; p; p = p->next) {
-			uint32_t **p_refs = ref_bitmap_at(&info->ref_bitmap,
-							  p->item);
 			if (p->item->object.flags & SEEN)
 				continue;
-			if (*p_refs == NULL || *p_refs == *refs)
-				*p_refs = *refs;
 			commit_list_insert(p->item, &head);
 		}
 	}
@@ -624,9 +625,9 @@ void assign_shallow_commits_to_refs(struct shallow_info *info,
 		post_assign_shallow(info, &pi.ref_bitmap, ref_status);
 
 	clear_ref_bitmap(&pi.ref_bitmap);
-	for (i = 0; i < pi.slab_count; i++)
-		free(pi.slab[i]);
-	free(pi.slab);
+	for (i = 0; i < pi.pool_count; i++)
+		free(pi.pools[i]);
+	free(pi.pools);
 	free(shallow);
 }
 
@@ -648,11 +649,11 @@ static int add_ref(const char *refname, const struct object_id *oid,
 
 static void update_refstatus(int *ref_status, int nr, uint32_t *bitmap)
 {
-	int i;
+	unsigned int i;
 	if (!ref_status)
 		return;
 	for (i = 0; i < nr; i++)
-		if (bitmap[i / 32] & (1 << (i % 32)))
+		if (bitmap[i / 32] & (1U << (i % 32)))
 			ref_status[i]++;
 }