pack-objects: move 'layer' into 'struct packing_data'

This reduces the size of 'struct object_entry' from 88 bytes
to 80 and therefore makes packing objects more efficient.

For example on a Linux repo with 12M objects,
`git pack-objects --all` needs extra 96MB memory even if the
layer feature is not used.

Helped-by: Jeff King <peff@peff.net>
Helped-by: Duy Nguyen <pclouds@gmail.com>
Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/pack-objects.c

@@ -611,7 +611,7 @@ static inline void add_to_write_order(struct object_entry **wo,
 			       unsigned int *endp,
 			       struct object_entry *e)
 {
-	if (e->filled || e->layer != write_layer)
+	if (e->filled || oe_layer(&to_pack, e) != write_layer)
 		return;
 	wo[(*endp)++] = e;
 	e->filled = 1;
@@ -714,7 +714,7 @@ static void compute_layer_order(struct object_entry **wo, unsigned int *wo_end)
 	 * Finally all the rest in really tight order
 	 */
 	for (i = last_untagged; i < to_pack.nr_objects; i++) {
-		if (!objects[i].filled && objects[i].layer == write_layer)
+		if (!objects[i].filled && oe_layer(&to_pack, &objects[i]) == write_layer)
 			add_family_to_write_order(wo, wo_end, &objects[i]);
 	}
 }

delta-islands.c

@@ -488,13 +488,13 @@ int compute_pack_layers(struct packing_data *to_pack)
 		struct object_entry *entry = &to_pack->objects[i];
 		khiter_t pos = kh_get_sha1(island_marks, entry->idx.oid.hash);
 
-		entry->layer = 1;
+		oe_set_layer(to_pack, entry, 1);
 
 		if (pos < kh_end(island_marks)) {
 			struct island_bitmap *bitmap = kh_value(island_marks, pos);
 
 			if (island_bitmap_get(bitmap, island_counter_core))
-				entry->layer = 0;
+				oe_set_layer(to_pack, entry, 0);
 		}
 	}
 

pack-objects.c

@@ -163,6 +163,9 @@ struct object_entry *packlist_alloc(struct packing_data *pdata,
 
 		if (pdata->tree_depth)
 			REALLOC_ARRAY(pdata->tree_depth, pdata->nr_alloc);
+
+		if (pdata->layer)
+			REALLOC_ARRAY(pdata->layer, pdata->nr_alloc);
 	}
 
 	new_entry = pdata->objects + pdata->nr_objects++;
@@ -181,5 +184,8 @@ struct object_entry *packlist_alloc(struct packing_data *pdata,
 	if (pdata->tree_depth)
 		pdata->tree_depth[pdata->nr_objects - 1] = 0;
 
+	if (pdata->layer)
+		pdata->layer[pdata->nr_objects - 1] = 0;
+
 	return new_entry;
 }

pack-objects.h

@@ -101,8 +101,6 @@ struct object_entry {
 	unsigned no_try_delta:1;
 	unsigned in_pack_type:TYPE_BITS; /* could be delta */
 
-	unsigned char layer;
-
 	unsigned preferred_base:1; /*
 				    * we do not pack this, but is available
 				    * to be used as the base object to delta
@@ -147,6 +145,7 @@ struct packing_data {
 
 	/* delta islands */
 	unsigned int *tree_depth;
+	unsigned char *layer;
 };
 
 void prepare_packing_data(struct packing_data *pdata);
@@ -369,4 +368,21 @@ static inline void oe_set_tree_depth(struct packing_data *pack,
 	pack->tree_depth[e - pack->objects] = tree_depth;
 }
 
+static inline unsigned char oe_layer(struct packing_data *pack,
+				     struct object_entry *e)
+{
+	if (!pack->layer)
+		return 0;
+	return pack->layer[e - pack->objects];
+}
+
+static inline void oe_set_layer(struct packing_data *pack,
+				struct object_entry *e,
+				unsigned char layer)
+{
+	if (!pack->layer)
+		ALLOC_ARRAY(pack->layer, pack->nr_objects);
+	pack->layer[e - pack->objects] = layer;
+}
+
 #endif