diff --git a/pack-bitmap-write.c b/pack-bitmap-write.c
index 1c8070f99c..1bcb3f98a4 100644
--- a/pack-bitmap-write.c
+++ b/pack-bitmap-write.c
@@ -32,6 +32,7 @@ struct bitmapped_commit {
 	struct commit *commit;
 	struct ewah_bitmap *bitmap;
 	struct ewah_bitmap *write_as;
+	struct ewah_bitmap *pseudo_merge_parents;
 	int flags;
 	int xor_offset;
 	uint32_t commit_pos;
@@ -89,6 +90,7 @@ void bitmap_writer_free(struct bitmap_writer *writer)
 	ewah_free(writer->tags);
 
 	kh_destroy_oid_map(writer->bitmaps);
+	free(writer->pos_cache);
 
 	kh_foreach_value(writer->pseudo_merge_commits, idx,
 			 free_pseudo_merge_commit_idx(idx));
@@ -101,6 +103,7 @@ void bitmap_writer_free(struct bitmap_writer *writer)
 		if (bc->write_as != bc->bitmap)
 			ewah_free(bc->write_as);
 		ewah_free(bc->bitmap);
+		ewah_free(bc->pseudo_merge_parents);
 	}
 	free(writer->selected);
 }
@@ -209,38 +212,116 @@ void bitmap_writer_push_commit(struct bitmap_writer *writer,
 	writer->selected[writer->selected_nr].write_as = NULL;
 	writer->selected[writer->selected_nr].flags = 0;
 	writer->selected[writer->selected_nr].pseudo_merge = pseudo_merge;
+	writer->selected[writer->selected_nr].pseudo_merge_parents = NULL;
 
 	writer->selected_nr++;
 }
 
+struct bitmap_pos_cache_entry {
+	struct object_id oid;
+	uint32_t pos;
+};
+
+#define BITMAP_POS_MIN_CACHE_SIZE (1U << 10)
+#define BITMAP_POS_MAX_CACHE_SIZE (1U << 21)
+#define BITMAP_POS_CACHE_VALID    (1U << 31)
+
+static void bitmap_writer_init_pos_cache(struct bitmap_writer *writer)
+{
+	if (writer->pos_cache)
+		return;
+
+	writer->pos_cache_nr = BITMAP_POS_MIN_CACHE_SIZE;
+
+	while (writer->pos_cache_nr < writer->to_pack->nr_objects &&
+	       writer->pos_cache_nr < BITMAP_POS_MAX_CACHE_SIZE)
+		writer->pos_cache_nr <<= 1;
+
+	CALLOC_ARRAY(writer->pos_cache, writer->pos_cache_nr);
+}
+
+static size_t bitmap_writer_pos_cache_slot(struct bitmap_writer *writer,
+					   const struct object_id *oid)
+{
+	return oidhash(oid) & (writer->pos_cache_nr - 1);
+}
+
+static bool bitmap_writer_pos_cache_valid(struct bitmap_writer *writer,
+					  size_t slot)
+{
+	return !!(writer->pos_cache[slot].pos & BITMAP_POS_CACHE_VALID);
+}
+
+static int find_cached_object_pos(struct bitmap_writer *writer,
+				  const struct object_id *oid, uint32_t *pos)
+{
+	size_t slot = bitmap_writer_pos_cache_slot(writer, oid);
+
+	if (bitmap_writer_pos_cache_valid(writer, slot) &&
+	    oideq(&writer->pos_cache[slot].oid, oid)) {
+		writer->pos_cache_hits++;
+		*pos = writer->pos_cache[slot].pos & ~BITMAP_POS_CACHE_VALID;
+		return 1;
+	}
+
+	writer->pos_cache_misses++;
+	return 0;
+}
+
+static uint32_t store_cached_object_pos(struct bitmap_writer *writer,
+					const struct object_id *oid,
+					uint32_t pos)
+{
+	size_t slot;
+
+	if (pos & BITMAP_POS_CACHE_VALID)
+		return pos; /* too large to cache */
+
+	slot = bitmap_writer_pos_cache_slot(writer, oid);
+
+	oidcpy(&writer->pos_cache[slot].oid, oid);
+	writer->pos_cache[slot].pos = pos | BITMAP_POS_CACHE_VALID;
+
+	return pos;
+}
+
 static uint32_t find_object_pos(struct bitmap_writer *writer,
 				const struct object_id *oid, int *found)
 {
 	struct object_entry *entry;
+	uint32_t pos;
+
+	bitmap_writer_init_pos_cache(writer);
+
+	if (find_cached_object_pos(writer, oid, &pos)) {
+		if (found)
+			*found = 1;
+		return pos;
+	}
 
 	entry = packlist_find(writer->to_pack, oid);
 	if (entry) {
 		uint32_t base_objects = 0;
+
 		if (writer->midx)
 			base_objects = writer->midx->num_objects +
 				writer->midx->num_objects_in_base;
-
-		if (found)
-			*found = 1;
-		return oe_in_pack_pos(writer->to_pack, entry) + base_objects;
+		pos = oe_in_pack_pos(writer->to_pack, entry) + base_objects;
 	} else if (writer->midx) {
-		uint32_t at, pos;
+		uint32_t at;
 
 		if (!bsearch_midx(oid, writer->midx, &at))
 			goto missing;
 		if (midx_to_pack_pos(writer->midx, at, &pos) < 0)
 			goto missing;
-
-		if (found)
-			*found = 1;
-		return pos;
+	} else {
+		goto missing;
 	}
 
+	if (found)
+		*found = 1;
+	return store_cached_object_pos(writer, oid, pos);
+
 missing:
 	if (found)
 		*found = 0;
@@ -249,11 +330,40 @@ missing:
 	return 0;
 }
 
+static int bitmapped_commit_date_cmp(const void *_a, const void *_b)
+{
+	const struct bitmapped_commit *a = _a;
+	const struct bitmapped_commit *b = _b;
+
+	if (a->commit->date < b->commit->date)
+		return -1;
+	if (a->commit->date > b->commit->date)
+		return 1;
+	return 0;
+}
+
 static void compute_xor_offsets(struct bitmap_writer *writer)
 {
 	static const int MAX_XOR_OFFSET_SEARCH = 10;
 
 	int i, next = 0;
+	int nr = bitmap_writer_nr_selected_commits(writer);
+
+	if (nr > 1) {
+		QSORT(writer->selected, nr, bitmapped_commit_date_cmp);
+
+		for (i = 0; i < nr; i++) {
+			struct bitmapped_commit *stored = &writer->selected[i];
+			khiter_t hash_pos = kh_get_oid_map(writer->bitmaps,
+							   stored->commit->object.oid);
+
+			if (hash_pos == kh_end(writer->bitmaps))
+				BUG("selected commit missing from bitmap map: %s",
+				    oid_to_hex(&stored->commit->object.oid));
+
+			kh_value(writer->bitmaps, hash_pos) = stored;
+		}
+	}
 
 	while (next < writer->selected_nr) {
 		struct bitmapped_commit *stored = &writer->selected[next];
@@ -336,13 +446,17 @@ static void bitmap_builder_init(struct bitmap_builder *bb,
 	revs.topo_order = 1;
 	revs.first_parent_only = 1;
 
-	for (i = 0; i < writer->selected_nr; i++) {
+	for (i = 0; i < bitmap_writer_nr_selected_commits(writer); i++) {
 		struct bitmapped_commit *bc = &writer->selected[i];
 		struct bb_commit *ent = bb_data_at(&bb->data, bc->commit);
 
+		if (bc->pseudo_merge)
+			BUG("unexpected pseudo-merge at %"PRIuMAX,
+			    (uintmax_t)i);
+
 		ent->selected = 1;
 		ent->maximal = 1;
-		ent->pseudo_merge = bc->pseudo_merge;
+		ent->pseudo_merge = 0;
 		ent->idx = i;
 
 		ent->commit_mask = bitmap_new();
@@ -456,22 +570,13 @@ static void bitmap_builder_clear(struct bitmap_builder *bb)
 
 static int fill_bitmap_tree(struct bitmap_writer *writer,
 			    struct bitmap *bitmap,
-			    struct tree *tree)
+			    struct tree *tree,
+			    uint32_t pos)
 {
 	int found;
-	uint32_t pos;
 	struct tree_desc desc;
 	struct name_entry entry;
 
-	/*
-	 * If our bit is already set, then there is nothing to do. Both this
-	 * tree and all of its children will be set.
-	 */
-	pos = find_object_pos(writer, &tree->object.oid, &found);
-	if (!found)
-		return -1;
-	if (bitmap_get(bitmap, pos))
-		return 0;
 	bitmap_set(bitmap, pos);
 
 	if (repo_parse_tree(writer->repo, tree) < 0)
@@ -482,8 +587,21 @@ static int fill_bitmap_tree(struct bitmap_writer *writer,
 	while (tree_entry(&desc, &entry)) {
 		switch (object_type(entry.mode)) {
 		case OBJ_TREE:
+			pos = find_object_pos(writer, &entry.oid, &found);
+			if (!found)
+				return -1;
+			if (bitmap_get(bitmap, pos)) {
+				/*
+				 * If our bit is already set, then there
+				 * is nothing to do. Both this tree and
+				 * all of its children will be set.
+				 */
+				break;
+			}
+
 			if (fill_bitmap_tree(writer, bitmap,
-					     lookup_tree(writer->repo, &entry.oid)) < 0)
+					     lookup_tree(writer->repo,
+							 &entry.oid), pos) < 0)
 				return -1;
 			break;
 		case OBJ_BLOB:
@@ -504,6 +622,11 @@ static int fill_bitmap_tree(struct bitmap_writer *writer,
 
 static int reused_bitmaps_nr;
 static int reused_pseudo_merge_bitmaps_nr;
+static int pseudo_merge_bitmap_nr;
+static int pseudo_merge_bitmap_parents;
+
+static int fill_bitmap_commit_calls_nr;
+static int fill_bitmap_commit_found_ancestor_nr;
 
 static int fill_bitmap_commit(struct bitmap_writer *writer,
 			      struct bb_commit *ent,
@@ -514,7 +637,14 @@ static int fill_bitmap_commit(struct bitmap_writer *writer,
 			      const uint32_t *mapping)
 {
 	int found;
+	int from_pseudo_merge = commit->object.flags & BITMAP_PSEUDO_MERGE;
 	uint32_t pos;
+
+	if (ent->pseudo_merge)
+		BUG("unexpected pseudo-merge commit in fill_bitmap_commit()");
+
+	fill_bitmap_commit_calls_nr++;
+
 	if (!ent->bitmap)
 		ent->bitmap = bitmap_new();
 
@@ -528,10 +658,7 @@ static int fill_bitmap_commit(struct bitmap_writer *writer,
 			struct ewah_bitmap *old;
 			struct bitmap *remapped = bitmap_new();
 
-			if (commit->object.flags & BITMAP_PSEUDO_MERGE)
-				old = pseudo_merge_bitmap_for_commit(old_bitmap, c);
-			else
-				old = bitmap_for_commit(old_bitmap, c);
+			old = bitmap_for_commit(old_bitmap, c);
 			/*
 			 * If this commit has an old bitmap, then translate that
 			 * bitmap and add its bits to this one. No need to walk
@@ -540,26 +667,65 @@ static int fill_bitmap_commit(struct bitmap_writer *writer,
 			if (old && !rebuild_bitmap(mapping, old, remapped)) {
 				bitmap_or(ent->bitmap, remapped);
 				bitmap_free(remapped);
-				if (commit->object.flags & BITMAP_PSEUDO_MERGE)
-					reused_pseudo_merge_bitmaps_nr++;
-				else
-					reused_bitmaps_nr++;
+				reused_bitmaps_nr++;
 				continue;
 			}
 			bitmap_free(remapped);
 		}
 
+		/*
+		 * If we encounter an ancestor for which we have already
+		 * computed a bitmap during this build (i.e. a regular
+		 * selected commit processed earlier in topo order), we can
+		 * short-circuit the walk: its stored bitmap already covers
+		 * the commit itself, its tree, and all of its ancestors.
+		 */
+		if (c != commit) {
+			khiter_t hash_pos = kh_get_oid_map(writer->bitmaps,
+							   c->object.oid);
+			if (hash_pos != kh_end(writer->bitmaps)) {
+				struct bitmapped_commit *stored =
+					kh_value(writer->bitmaps, hash_pos);
+				if (stored && stored->bitmap) {
+					fill_bitmap_commit_found_ancestor_nr++;
+					bitmap_or_ewah(ent->bitmap,
+						       stored->bitmap);
+					continue;
+				}
+			}
+		}
+
 		/*
 		 * Mark ourselves and queue our tree. The commit
 		 * walk ensures we cover all parents.
 		 */
 		if (!(c->object.flags & BITMAP_PSEUDO_MERGE)) {
+			struct tree *tree;
+
+			if (from_pseudo_merge && !c->object.parsed) {
+				/*
+				 * Commits reachable from selected
+				 * non-pseudo-merges are already parsed
+				 * by the regular bitmap build.
+				 *
+				 * However, pseudo-merge fills can also
+				 * reach commits that were not covered
+				 * there, so parse any such leftovers
+				 * before reading their tree or parents.
+				 */
+				if (repo_parse_commit(writer->repo, c))
+					return -1;
+			}
+
 			pos = find_object_pos(writer, &c->object.oid, &found);
 			if (!found)
 				return -1;
 			bitmap_set(ent->bitmap, pos);
-			prio_queue_put(tree_queue,
-				       repo_get_commit_tree(writer->repo, c));
+
+			tree = repo_get_commit_tree(writer->repo, c);
+			if (!tree)
+				return -1;
+			prio_queue_put(tree_queue, tree);
 		}
 
 		for (p = c->parents; p; p = p->next) {
@@ -575,13 +741,158 @@ static int fill_bitmap_commit(struct bitmap_writer *writer,
 	}
 
 	while (tree_queue->nr) {
-		if (fill_bitmap_tree(writer, ent->bitmap,
-				     prio_queue_get(tree_queue)) < 0)
+		struct tree *t = prio_queue_get(tree_queue);
+		int found;
+
+		pos = find_object_pos(writer, &t->object.oid, &found);
+		if (!found)
+			return -1;
+		if (bitmap_get(ent->bitmap, pos)) {
+			/*
+			 * If our bit is already set, then there is
+			 * nothing to do. Both this tree and all of its
+			 * children will be set.
+			 */
+			continue;
+		}
+
+		if (fill_bitmap_tree(writer, ent->bitmap, t, pos) < 0)
 			return -1;
 	}
 	return 0;
 }
 
+static int reuse_pseudo_merge_bitmap(struct bitmap_index *old_bitmap,
+				     const uint32_t *mapping,
+				     struct commit *merge,
+				     struct ewah_bitmap **out)
+{
+	struct ewah_bitmap *old;
+	struct bitmap *remapped;
+
+	if (!old_bitmap || !mapping)
+		return 0;
+
+	old = pseudo_merge_bitmap_for_commit(old_bitmap, merge);
+	if (!old)
+		return 0;
+
+	remapped = bitmap_new();
+	if (rebuild_bitmap(mapping, old, remapped) < 0) {
+		bitmap_free(remapped);
+		return 0;
+	}
+
+	*out = bitmap_to_ewah(remapped);
+	bitmap_free(remapped);
+	reused_pseudo_merge_bitmaps_nr++;
+	return 1;
+}
+
+static int build_pseudo_merge_bitmap(struct bitmap_writer *writer,
+				     struct bitmap_index *old_bitmap,
+				     const uint32_t *mapping,
+				     struct commit *merge,
+				     struct ewah_bitmap **out)
+{
+	struct bb_commit ent = { 0 };
+	struct prio_queue queue = { NULL };
+	struct prio_queue tree_queue = { NULL };
+	unsigned parents = commit_list_count(merge->parents);
+	int ret;
+
+	ent.bitmap = bitmap_new();
+
+	pseudo_merge_bitmap_nr++;
+	pseudo_merge_bitmap_parents += parents;
+
+	if (reuse_pseudo_merge_bitmap(old_bitmap, mapping, merge, out)) {
+		ret = 0;
+		goto done;
+	}
+
+	ret = fill_bitmap_commit(writer, &ent, merge, &queue, &tree_queue,
+				 old_bitmap, mapping);
+
+	if (!ret)
+		*out = bitmap_to_ewah(ent.bitmap);
+
+done:
+	bitmap_free(ent.bitmap);
+	clear_prio_queue(&queue);
+	clear_prio_queue(&tree_queue);
+
+	return ret;
+}
+
+static int build_pseudo_merge_bitmaps(struct bitmap_writer *writer,
+				      struct bitmap_index *old_bitmap,
+				      const uint32_t *mapping,
+				      int *nr_stored)
+{
+	size_t i = bitmap_writer_nr_selected_commits(writer);
+	int ret = 0;
+
+	if (!writer->pseudo_merges_nr)
+		return 0;
+
+	trace2_region_enter("pack-bitmap-write", "building_pseudo_merge_bitmaps",
+			    writer->repo);
+
+	for (; i < writer->selected_nr; i++) {
+		struct bitmapped_commit *merge = &writer->selected[i];
+		struct commit_list *p;
+		struct bitmap *parents = bitmap_new();
+		struct ewah_bitmap *objects = NULL;
+
+		if (!merge->pseudo_merge)
+			BUG("found non-pseudo merge commit at %"PRIuMAX,
+			    (uintmax_t)i);
+
+		for (p = merge->commit->parents; p; p = p->next) {
+			int found;
+			uint32_t pos = find_object_pos(writer,
+						       &p->item->object.oid,
+						       &found);
+			if (!found) {
+				bitmap_free(parents);
+				ret = -1;
+				goto done;
+			}
+			bitmap_set(parents, pos);
+		}
+
+		merge->pseudo_merge_parents = bitmap_to_ewah(parents);
+		bitmap_free(parents);
+
+		if (build_pseudo_merge_bitmap(writer, old_bitmap, mapping,
+					      merge->commit, &objects) < 0) {
+			ret = -1;
+			goto done;
+		}
+		merge->bitmap = objects;
+
+		(*nr_stored)++;
+		display_progress(writer->progress, *nr_stored);
+	}
+
+done:
+	trace2_region_leave("pack-bitmap-write", "building_pseudo_merge_bitmaps",
+			    writer->repo);
+
+	trace2_data_intmax("pack-bitmap-write", writer->repo,
+			   "pseudo_merge_bitmap_nr",
+			   pseudo_merge_bitmap_nr);
+	trace2_data_intmax("pack-bitmap-write", writer->repo,
+			   "building_bitmaps_pseudo_merge_reused",
+			   reused_pseudo_merge_bitmaps_nr);
+	trace2_data_intmax("pack-bitmap-write", writer->repo,
+			   "pseudo_merge_bitmap_parents",
+			   pseudo_merge_bitmap_parents);
+
+	return ret;
+}
+
 static void store_selected(struct bitmap_writer *writer,
 			   struct bb_commit *ent, struct commit *commit)
 {
@@ -616,6 +927,10 @@ int bitmap_writer_build(struct bitmap_writer *writer)
 		writer->progress = start_progress(writer->repo,
 						  "Building bitmaps",
 						  writer->selected_nr);
+
+	writer->pos_cache_hits = 0;
+	writer->pos_cache_misses = 0;
+
 	trace2_region_enter("pack-bitmap-write", "building_bitmaps_total",
 			    writer->repo);
 
@@ -661,6 +976,10 @@ int bitmap_writer_build(struct bitmap_writer *writer)
 			bitmap_free(ent->bitmap);
 		ent->bitmap = NULL;
 	}
+	if (closed &&
+	    build_pseudo_merge_bitmaps(writer, old_bitmap, mapping,
+				       &nr_stored) < 0)
+		closed = 0;
 	clear_prio_queue(&queue);
 	clear_prio_queue(&tree_queue);
 	bitmap_builder_clear(&bb);
@@ -672,8 +991,15 @@ int bitmap_writer_build(struct bitmap_writer *writer)
 	trace2_data_intmax("pack-bitmap-write", writer->repo,
 			   "building_bitmaps_reused", reused_bitmaps_nr);
 	trace2_data_intmax("pack-bitmap-write", writer->repo,
-			   "building_bitmaps_pseudo_merge_reused",
-			   reused_pseudo_merge_bitmaps_nr);
+			   "fill_bitmap_commit_calls_nr",
+			   fill_bitmap_commit_calls_nr);
+	trace2_data_intmax("pack-bitmap-write", writer->repo,
+			   "fill_bitmap_commit_found_ancestor_nr",
+			   fill_bitmap_commit_found_ancestor_nr);
+	trace2_data_intmax("pack-bitmap-write", writer->repo,
+			   "bitmap_pos_cache_hits", writer->pos_cache_hits);
+	trace2_data_intmax("pack-bitmap-write", writer->repo,
+			   "bitmap_pos_cache_misses", writer->pos_cache_misses);
 
 	stop_progress(&writer->progress);
 
@@ -837,42 +1163,29 @@ static void write_pseudo_merges(struct bitmap_writer *writer,
 				struct hashfile *f)
 {
 	struct oid_array commits = OID_ARRAY_INIT;
-	struct bitmap **commits_bitmap = NULL;
 	off_t *pseudo_merge_ofs = NULL;
 	off_t start, table_start, next_ext;
 
 	uint32_t base = bitmap_writer_nr_selected_commits(writer);
 	size_t i, j = 0;
 
-	CALLOC_ARRAY(commits_bitmap, writer->pseudo_merges_nr);
 	CALLOC_ARRAY(pseudo_merge_ofs, writer->pseudo_merges_nr);
 
-	for (i = 0; i < writer->pseudo_merges_nr; i++) {
-		struct bitmapped_commit *merge = &writer->selected[base + i];
-		struct commit_list *p;
-
-		if (!merge->pseudo_merge)
-			BUG("found non-pseudo merge commit at %"PRIuMAX, (uintmax_t)i);
-
-		commits_bitmap[i] = bitmap_new();
-
-		for (p = merge->commit->parents; p; p = p->next)
-			bitmap_set(commits_bitmap[i],
-				   find_object_pos(writer, &p->item->object.oid,
-						   NULL));
-	}
-
 	start = hashfile_total(f);
 
 	for (i = 0; i < writer->pseudo_merges_nr; i++) {
-		struct ewah_bitmap *commits_ewah = bitmap_to_ewah(commits_bitmap[i]);
+		struct bitmapped_commit *merge = &writer->selected[base + i];
+
+		if (!merge->pseudo_merge)
+			BUG("found non-pseudo merge commit at %"PRIuMAX, (uintmax_t)i);
+
+		if (!merge->pseudo_merge_parents || !merge->bitmap)
+			BUG("missing pseudo-merge bitmap for commit %s",
+			    oid_to_hex(&merge->commit->object.oid));
 
 		pseudo_merge_ofs[i] = hashfile_total(f);
-
-		dump_bitmap(f, commits_ewah);
-		dump_bitmap(f, writer->selected[base+i].write_as);
-
-		ewah_free(commits_ewah);
+		dump_bitmap(f, merge->pseudo_merge_parents);
+		dump_bitmap(f, merge->bitmap);
 	}
 
 	next_ext = st_add(hashfile_total(f),
@@ -955,12 +1268,8 @@ static void write_pseudo_merges(struct bitmap_writer *writer,
 	hashwrite_be64(f, table_start - start);
 	hashwrite_be64(f, hashfile_total(f) - start + sizeof(uint64_t));
 
-	for (i = 0; i < writer->pseudo_merges_nr; i++)
-		bitmap_free(commits_bitmap[i]);
-
 	oid_array_clear(&commits);
 	free(pseudo_merge_ofs);
-	free(commits_bitmap);
 }
 
 static int table_cmp(const void *_va, const void *_vb, void *_data)
diff --git a/pack-bitmap.h b/pack-bitmap.h
index a95e1c2d11..19a8655457 100644
--- a/pack-bitmap.h
+++ b/pack-bitmap.h
@@ -132,6 +132,8 @@ int bitmap_has_oid_in_uninteresting(struct bitmap_index *, const struct object_i
 
 off_t get_disk_usage_from_bitmap(struct bitmap_index *, struct rev_info *);
 
+struct bitmap_pos_cache_entry;
+
 struct bitmap_writer {
 	struct repository *repo;
 	struct ewah_bitmap *commits;
@@ -143,6 +145,11 @@ struct bitmap_writer {
 	struct packing_data *to_pack;
 	struct multi_pack_index *midx; /* if appending to a MIDX chain */
 
+	struct bitmap_pos_cache_entry *pos_cache;
+	size_t pos_cache_nr;
+	uint64_t pos_cache_hits;
+	uint64_t pos_cache_misses;
+
 	struct bitmapped_commit *selected;
 	unsigned int selected_nr, selected_alloc;