Merge branch 'nd/pack-objects-pack-struct'

"git pack-objects" needs to allocate tons of "struct object_entry"
while doing its work, and shrinking its size helps the performance
quite a bit.

* nd/pack-objects-pack-struct:
  ci: exercise the whole test suite with uncommon code in pack-objects
  pack-objects: reorder members to shrink struct object_entry
  pack-objects: shrink delta_size field in struct object_entry
  pack-objects: shrink size field in struct object_entry
  pack-objects: clarify the use of object_entry::size
  pack-objects: don't check size when the object is bad
  pack-objects: shrink z_delta_size field in struct object_entry
  pack-objects: refer to delta objects by index instead of pointer
  pack-objects: move in_pack out of struct object_entry
  pack-objects: move in_pack_pos out of struct object_entry
  pack-objects: use bitfield for object_entry::depth
  pack-objects: use bitfield for object_entry::dfs_state
  pack-objects: turn type and in_pack_type to bitfields
  pack-objects: a bit of document about struct object_entry
  read-cache.c: make $GIT_TEST_SPLIT_INDEX boolean

16 files changed, 656 insertions, 167 deletions

diff --git a/Documentation/config.txt b/Documentation/config.txt
index 8df48d0c3e..4874364f17 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -2472,6 +2472,7 @@ pack.window::
 pack.depth::
 	The maximum delta depth used by linkgit:git-pack-objects[1] when no
 	maximum depth is given on the command line. Defaults to 50.
+	Maximum value is 4095.
 
 pack.windowMemory::
 	The maximum size of memory that is consumed by each thread
@@ -2508,7 +2509,8 @@ pack.deltaCacheLimit::
 	The maximum size of a delta, that is cached in
 	linkgit:git-pack-objects[1]. This cache is used to speed up the
 	writing object phase by not having to recompute the final delta
-	result once the best match for all objects is found. Defaults to 1000.
+	result once the best match for all objects is found.
+	Defaults to 1000. Maximum value is 65535.
 
 pack.threads::
 	Specifies the number of threads to spawn when searching for best
diff --git a/Documentation/git-pack-objects.txt b/Documentation/git-pack-objects.txt
index 403524652a..6bfac6b7ff 100644
--- a/Documentation/git-pack-objects.txt
+++ b/Documentation/git-pack-objects.txt
@@ -96,7 +96,9 @@ base-name::
 	it too deep affects the performance on the unpacker
 	side, because delta data needs to be applied that many
 	times to get to the necessary object.
-	The default value for --window is 10 and --depth is 50.
++
+The default value for --window is 10 and --depth is 50. The maximum
+depth is 4095.
 
 --window-memory=<n>::
 	This option provides an additional limit on top of `--window`;
diff --git a/Documentation/git-repack.txt b/Documentation/git-repack.txt
index ce497d9d12..d90e7907f4 100644
--- a/Documentation/git-repack.txt
+++ b/Documentation/git-repack.txt
@@ -90,7 +90,9 @@ other objects in that pack they already have locally.
 	space. `--depth` limits the maximum delta depth; making it too deep
 	affects the performance on the unpacker side, because delta data needs
 	to be applied that many times to get to the necessary object.
-	The default value for --window is 10 and --depth is 50.
++
+The default value for --window is 10 and --depth is 50. The maximum
+depth is 4095.
 
 --threads=<n>::
 	This option is passed through to `git pack-objects`.
diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
index 4ce6a93281..8552d7e42e 100644
--- a/builtin/pack-objects.c
+++ b/builtin/pack-objects.c
@@ -32,6 +32,18 @@
 #include "object-store.h"
 #include "dir.h"
 
+#define IN_PACK(obj) oe_in_pack(&to_pack, obj)
+#define SIZE(obj) oe_size(&to_pack, obj)
+#define SET_SIZE(obj,size) oe_set_size(&to_pack, obj, size)
+#define DELTA_SIZE(obj) oe_delta_size(&to_pack, obj)
+#define DELTA(obj) oe_delta(&to_pack, obj)
+#define DELTA_CHILD(obj) oe_delta_child(&to_pack, obj)
+#define DELTA_SIBLING(obj) oe_delta_sibling(&to_pack, obj)
+#define SET_DELTA(obj, val) oe_set_delta(&to_pack, obj, val)
+#define SET_DELTA_SIZE(obj, val) oe_set_delta_size(&to_pack, obj, val)
+#define SET_DELTA_CHILD(obj, val) oe_set_delta_child(&to_pack, obj, val)
+#define SET_DELTA_SIBLING(obj, val) oe_set_delta_sibling(&to_pack, obj, val)
+
 static const char *pack_usage[] = {
 	N_("git pack-objects --stdout [<options>...] [< <ref-list> | < <object-list>]"),
 	N_("git pack-objects [<options>...] <base-name> [< <ref-list> | < <object-list>]"),
@@ -129,13 +141,14 @@ static void *get_delta(struct object_entry *entry)
 	buf = read_object_file(&entry->idx.oid, &type, &size);
 	if (!buf)
 		die("unable to read %s", oid_to_hex(&entry->idx.oid));
-	base_buf = read_object_file(&entry->delta->idx.oid, &type, &base_size);
+	base_buf = read_object_file(&DELTA(entry)->idx.oid, &type,
+				    &base_size);
 	if (!base_buf)
 		die("unable to read %s",
-		    oid_to_hex(&entry->delta->idx.oid));
+		    oid_to_hex(&DELTA(entry)->idx.oid));
 	delta_buf = diff_delta(base_buf, base_size,
 			       buf, size, &delta_size, 0);
-	if (!delta_buf || delta_size != entry->delta_size)
+	if (!delta_buf || delta_size != DELTA_SIZE(entry))
 		die("delta size changed");
 	free(buf);
 	free(base_buf);
@@ -268,8 +281,8 @@ static unsigned long write_no_reuse_object(struct hashfile *f, struct object_ent
 	struct git_istream *st = NULL;
 
 	if (!usable_delta) {
-		if (entry->type == OBJ_BLOB &&
-		    entry->size > big_file_threshold &&
+		if (oe_type(entry) == OBJ_BLOB &&
+		    oe_size_greater_than(&to_pack, entry, big_file_threshold) &&
 		    (st = open_istream(&entry->idx.oid, &type, &size, NULL)) != NULL)
 			buf = NULL;
 		else {
@@ -285,15 +298,15 @@ static unsigned long write_no_reuse_object(struct hashfile *f, struct object_ent
 		FREE_AND_NULL(entry->delta_data);
 		entry->z_delta_size = 0;
 	} else if (entry->delta_data) {
-		size = entry->delta_size;
+		size = DELTA_SIZE(entry);
 		buf = entry->delta_data;
 		entry->delta_data = NULL;
-		type = (allow_ofs_delta && entry->delta->idx.offset) ?
+		type = (allow_ofs_delta && DELTA(entry)->idx.offset) ?
 			OBJ_OFS_DELTA : OBJ_REF_DELTA;
 	} else {
 		buf = get_delta(entry);
-		size = entry->delta_size;
-		type = (allow_ofs_delta && entry->delta->idx.offset) ?
+		size = DELTA_SIZE(entry);
+		type = (allow_ofs_delta && DELTA(entry)->idx.offset) ?
 			OBJ_OFS_DELTA : OBJ_REF_DELTA;
 	}
 
@@ -317,7 +330,7 @@ static unsigned long write_no_reuse_object(struct hashfile *f, struct object_ent
 		 * encoding of the relative offset for the delta
 		 * base from this object's position in the pack.
 		 */
-		off_t ofs = entry->idx.offset - entry->delta->idx.offset;
+		off_t ofs = entry->idx.offset - DELTA(entry)->idx.offset;
 		unsigned pos = sizeof(dheader) - 1;
 		dheader[pos] = ofs & 127;
 		while (ofs >>= 7)
@@ -343,7 +356,7 @@ static unsigned long write_no_reuse_object(struct hashfile *f, struct object_ent
 			return 0;
 		}
 		hashwrite(f, header, hdrlen);
-		hashwrite(f, entry->delta->idx.oid.hash, 20);
+		hashwrite(f, DELTA(entry)->idx.oid.hash, 20);
 		hdrlen += 20;
 	} else {
 		if (limit && hdrlen + datalen + 20 >= limit) {
@@ -369,21 +382,22 @@ static unsigned long write_no_reuse_object(struct hashfile *f, struct object_ent
 static off_t write_reuse_object(struct hashfile *f, struct object_entry *entry,
 				unsigned long limit, int usable_delta)
 {
-	struct packed_git *p = entry->in_pack;
+	struct packed_git *p = IN_PACK(entry);
 	struct pack_window *w_curs = NULL;
 	struct revindex_entry *revidx;
 	off_t offset;
-	enum object_type type = entry->type;
+	enum object_type type = oe_type(entry);
 	off_t datalen;
 	unsigned char header[MAX_PACK_OBJECT_HEADER],
 		      dheader[MAX_PACK_OBJECT_HEADER];
 	unsigned hdrlen;
+	unsigned long entry_size = SIZE(entry);
 
-	if (entry->delta)
-		type = (allow_ofs_delta && entry->delta->idx.offset) ?
+	if (DELTA(entry))
+		type = (allow_ofs_delta && DELTA(entry)->idx.offset) ?
 			OBJ_OFS_DELTA : OBJ_REF_DELTA;
 	hdrlen = encode_in_pack_object_header(header, sizeof(header),
-					      type, entry->size);
+					      type, entry_size);
 
 	offset = entry->in_pack_offset;
 	revidx = find_pack_revindex(p, offset);
@@ -400,7 +414,7 @@ static off_t write_reuse_object(struct hashfile *f, struct object_entry *entry,
 	datalen -= entry->in_pack_header_size;
 
 	if (!pack_to_stdout && p->index_version == 1 &&
-	    check_pack_inflate(p, &w_curs, offset, datalen, entry->size)) {
+	    check_pack_inflate(p, &w_curs, offset, datalen, entry_size)) {
 		error("corrupt packed object for %s",
 		      oid_to_hex(&entry->idx.oid));
 		unuse_pack(&w_curs);
@@ -408,7 +422,7 @@ static off_t write_reuse_object(struct hashfile *f, struct object_entry *entry,
 	}
 
 	if (type == OBJ_OFS_DELTA) {
-		off_t ofs = entry->idx.offset - entry->delta->idx.offset;
+		off_t ofs = entry->idx.offset - DELTA(entry)->idx.offset;
 		unsigned pos = sizeof(dheader) - 1;
 		dheader[pos] = ofs & 127;
 		while (ofs >>= 7)
@@ -427,7 +441,7 @@ static off_t write_reuse_object(struct hashfile *f, struct object_entry *entry,
 			return 0;
 		}
 		hashwrite(f, header, hdrlen);
-		hashwrite(f, entry->delta->idx.oid.hash, 20);
+		hashwrite(f, DELTA(entry)->idx.oid.hash, 20);
 		hdrlen += 20;
 		reused_delta++;
 	} else {
@@ -467,28 +481,29 @@ static off_t write_object(struct hashfile *f,
 	else
 		limit = pack_size_limit - write_offset;
 
-	if (!entry->delta)
+	if (!DELTA(entry))
 		usable_delta = 0;	/* no delta */
 	else if (!pack_size_limit)
 	       usable_delta = 1;	/* unlimited packfile */
-	else if (entry->delta->idx.offset == (off_t)-1)
+	else if (DELTA(entry)->idx.offset == (off_t)-1)
 		usable_delta = 0;	/* base was written to another pack */
-	else if (entry->delta->idx.offset)
+	else if (DELTA(entry)->idx.offset)
 		usable_delta = 1;	/* base already exists in this pack */
 	else
 		usable_delta = 0;	/* base could end up in another pack */
 
 	if (!reuse_object)
 		to_reuse = 0;	/* explicit */
-	else if (!entry->in_pack)
+	else if (!IN_PACK(entry))
 		to_reuse = 0;	/* can't reuse what we don't have */
-	else if (entry->type == OBJ_REF_DELTA || entry->type == OBJ_OFS_DELTA)
+	else if (oe_type(entry) == OBJ_REF_DELTA ||
+		 oe_type(entry) == OBJ_OFS_DELTA)
 				/* check_object() decided it for us ... */
 		to_reuse = usable_delta;
 				/* ... but pack split may override that */
-	else if (entry->type != entry->in_pack_type)
+	else if (oe_type(entry) != entry->in_pack_type)
 		to_reuse = 0;	/* pack has delta which is unusable */
-	else if (entry->delta)
+	else if (DELTA(entry))
 		to_reuse = 0;	/* we want to pack afresh */
 	else
 		to_reuse = 1;	/* we have it in-pack undeltified,
@@ -540,12 +555,12 @@ static enum write_one_status write_one(struct hashfile *f,
 	}
 
 	/* if we are deltified, write out base object first. */
-	if (e->delta) {
+	if (DELTA(e)) {
 		e->idx.offset = 1; /* now recurse */
-		switch (write_one(f, e->delta, offset)) {
+		switch (write_one(f, DELTA(e), offset)) {
 		case WRITE_ONE_RECURSIVE:
 			/* we cannot depend on this one */
-			e->delta = NULL;
+			SET_DELTA(e, NULL);
 			break;
 		default:
 			break;
@@ -607,34 +622,34 @@ static void add_descendants_to_write_order(struct object_entry **wo,
 			/* add this node... */
 			add_to_write_order(wo, endp, e);
 			/* all its siblings... */
-			for (s = e->delta_sibling; s; s = s->delta_sibling) {
+			for (s = DELTA_SIBLING(e); s; s = DELTA_SIBLING(s)) {
 				add_to_write_order(wo, endp, s);
 			}
 		}
 		/* drop down a level to add left subtree nodes if possible */
-		if (e->delta_child) {
+		if (DELTA_CHILD(e)) {
 			add_to_order = 1;
-			e = e->delta_child;
+			e = DELTA_CHILD(e);
 		} else {
 			add_to_order = 0;
 			/* our sibling might have some children, it is next */
-			if (e->delta_sibling) {
-				e = e->delta_sibling;
+			if (DELTA_SIBLING(e)) {
+				e = DELTA_SIBLING(e);
 				continue;
 			}
 			/* go back to our parent node */
-			e = e->delta;
-			while (e && !e->delta_sibling) {
+			e = DELTA(e);
+			while (e && !DELTA_SIBLING(e)) {
 				/* we're on the right side of a subtree, keep
 				 * going up until we can go right again */
-				e = e->delta;
+				e = DELTA(e);
 			}
 			if (!e) {
 				/* done- we hit our original root node */
 				return;
 			}
 			/* pass it off to sibling at this level */
-			e = e->delta_sibling;
+			e = DELTA_SIBLING(e);
 		}
 	};
 }
@@ -645,7 +660,7 @@ static void add_family_to_write_order(struct object_entry **wo,
 {
 	struct object_entry *root;
 
-	for (root = e; root->delta; root = root->delta)
+	for (root = e; DELTA(root); root = DELTA(root))
 		; /* nothing */
 	add_descendants_to_write_order(wo, endp, root);
 }
@@ -660,8 +675,8 @@ static struct object_entry **compute_write_order(void)
 	for (i = 0; i < to_pack.nr_objects; i++) {
 		objects[i].tagged = 0;
 		objects[i].filled = 0;
-		objects[i].delta_child = NULL;
-		objects[i].delta_sibling = NULL;
+		SET_DELTA_CHILD(&objects[i], NULL);
+		SET_DELTA_SIBLING(&objects[i], NULL);
 	}
 
 	/*
@@ -671,11 +686,11 @@ static struct object_entry **compute_write_order(void)
 	 */
 	for (i = to_pack.nr_objects; i > 0;) {
 		struct object_entry *e = &objects[--i];
-		if (!e->delta)
+		if (!DELTA(e))
 			continue;
 		/* Mark me as the first child */
-		e->delta_sibling = e->delta->delta_child;
-		e->delta->delta_child = e;
+		e->delta_sibling_idx = DELTA(e)->delta_child_idx;
+		SET_DELTA_CHILD(DELTA(e), e);
 	}
 
 	/*
@@ -707,8 +722,8 @@ static struct object_entry **compute_write_order(void)
 	 * And then all remaining commits and tags.
 	 */
 	for (i = last_untagged; i < to_pack.nr_objects; i++) {
-		if (objects[i].type != OBJ_COMMIT &&
-		    objects[i].type != OBJ_TAG)
+		if (oe_type(&objects[i]) != OBJ_COMMIT &&
+		    oe_type(&objects[i]) != OBJ_TAG)
 			continue;
 		add_to_write_order(wo, &wo_end, &objects[i]);
 	}
@@ -717,7 +732,7 @@ static struct object_entry **compute_write_order(void)
 	 * And then all the trees.
 	 */
 	for (i = last_untagged; i < to_pack.nr_objects; i++) {
-		if (objects[i].type != OBJ_TREE)
+		if (oe_type(&objects[i]) != OBJ_TREE)
 			continue;
 		add_to_write_order(wo, &wo_end, &objects[i]);
 	}
@@ -880,7 +895,8 @@ static void write_pack_file(void)
 
 			if (write_bitmap_index) {
 				bitmap_writer_set_checksum(oid.hash);
-				bitmap_writer_build_type_index(written_list, nr_written);
+				bitmap_writer_build_type_index(
+					&to_pack, written_list, nr_written);
 			}
 
 			finish_tmp_packfile(&tmpname, pack_tmp_name,
@@ -1071,14 +1087,13 @@ static void create_object_entry(const struct object_id *oid,
 
 	entry = packlist_alloc(&to_pack, oid->hash, index_pos);
 	entry->hash = hash;
-	if (type)
-		entry->type = type;
+	oe_set_type(entry, type);
 	if (exclude)
 		entry->preferred_base = 1;
 	else
 		nr_result++;
 	if (found_pack) {
-		entry->in_pack = found_pack;
+		oe_set_in_pack(&to_pack, entry, found_pack);
 		entry->in_pack_offset = found_offset;
 	}
 
@@ -1403,8 +1418,10 @@ static void cleanup_preferred_base(void)
 
 static void check_object(struct object_entry *entry)
 {
-	if (entry->in_pack) {
-		struct packed_git *p = entry->in_pack;
+	unsigned long canonical_size;
+
+	if (IN_PACK(entry)) {
+		struct packed_git *p = IN_PACK(entry);
 		struct pack_window *w_curs = NULL;
 		const unsigned char *base_ref = NULL;
 		struct object_entry *base_entry;
@@ -1412,6 +1429,8 @@ static void check_object(struct object_entry *entry)
 		unsigned long avail;
 		off_t ofs;
 		unsigned char *buf, c;
+		enum object_type type;
+		unsigned long in_pack_size;
 
 		buf = use_pack(p, &w_curs, entry->in_pack_offset, &avail);
 
@@ -1420,11 +1439,15 @@ static void check_object(struct object_entry *entry)
 		 * since non-delta representations could still be reused.
 		 */
 		used = unpack_object_header_buffer(buf, avail,
-						   &entry->in_pack_type,
-						   &entry->size);
+						   &type,
+						   &in_pack_size);
 		if (used == 0)
 			goto give_up;
 
+		if (type < 0)
+			BUG("invalid type %d", type);
+		entry->in_pack_type = type;
+
 		/*
 		 * Determine if this is a delta and if so whether we can
 		 * reuse it or not.  Otherwise let's find out as cheaply as
@@ -1433,9 +1456,10 @@ static void check_object(struct object_entry *entry)
 		switch (entry->in_pack_type) {
 		default:
 			/* Not a delta hence we've already got all we need. */
-			entry->type = entry->in_pack_type;
+			oe_set_type(entry, entry->in_pack_type);
+			SET_SIZE(entry, in_pack_size);
 			entry->in_pack_header_size = used;
-			if (entry->type < OBJ_COMMIT || entry->type > OBJ_BLOB)
+			if (oe_type(entry) < OBJ_COMMIT || oe_type(entry) > OBJ_BLOB)
 				goto give_up;
 			unuse_pack(&w_curs);
 			return;
@@ -1489,25 +1513,29 @@ static void check_object(struct object_entry *entry)
 			 * deltify other objects against, in order to avoid
 			 * circular deltas.
 			 */
-			entry->type = entry->in_pack_type;
-			entry->delta = base_entry;
-			entry->delta_size = entry->size;
-			entry->delta_sibling = base_entry->delta_child;
-			base_entry->delta_child = entry;
+			oe_set_type(entry, entry->in_pack_type);
+			SET_SIZE(entry, in_pack_size); /* delta size */
+			SET_DELTA(entry, base_entry);
+			SET_DELTA_SIZE(entry, in_pack_size);
+			entry->delta_sibling_idx = base_entry->delta_child_idx;
+			SET_DELTA_CHILD(base_entry, entry);
 			unuse_pack(&w_curs);
 			return;
 		}
 
-		if (entry->type) {
+		if (oe_type(entry)) {
+			off_t delta_pos;
+
 			/*
 			 * This must be a delta and we already know what the
 			 * final object type is.  Let's extract the actual
 			 * object size from the delta header.
 			 */
-			entry->size = get_size_from_delta(p, &w_curs,
-					entry->in_pack_offset + entry->in_pack_header_size);
-			if (entry->size == 0)
+			delta_pos = entry->in_pack_offset + entry->in_pack_header_size;
+			canonical_size = get_size_from_delta(p, &w_curs, delta_pos);
+			if (canonical_size == 0)
 				goto give_up;
+			SET_SIZE(entry, canonical_size);
 			unuse_pack(&w_curs);
 			return;
 		}
@@ -1521,28 +1549,34 @@ static void check_object(struct object_entry *entry)
 		unuse_pack(&w_curs);
 	}
 
-	entry->type = oid_object_info(the_repository, &entry->idx.oid,
-				      &entry->size);
-	/*
-	 * The error condition is checked in prepare_pack().  This is
-	 * to permit a missing preferred base object to be ignored
-	 * as a preferred base.  Doing so can result in a larger
-	 * pack file, but the transfer will still take place.
-	 */
+	oe_set_type(entry,
+		    oid_object_info(the_repository, &entry->idx.oid, &canonical_size));
+	if (entry->type_valid) {
+		SET_SIZE(entry, canonical_size);
+	} else {
+		/*
+		 * Bad object type is checked in prepare_pack().  This is
+		 * to permit a missing preferred base object to be ignored
+		 * as a preferred base.  Doing so can result in a larger
+		 * pack file, but the transfer will still take place.
+		 */
+	}
 }
 
 static int pack_offset_sort(const void *_a, const void *_b)
 {
 	const struct object_entry *a = *(struct object_entry **)_a;
 	const struct object_entry *b = *(struct object_entry **)_b;
+	const struct packed_git *a_in_pack = IN_PACK(a);
+	const struct packed_git *b_in_pack = IN_PACK(b);
 
 	/* avoid filesystem trashing with loose objects */
-	if (!a->in_pack && !b->in_pack)
+	if (!a_in_pack && !b_in_pack)
 		return oidcmp(&a->idx.oid, &b->idx.oid);
 
-	if (a->in_pack < b->in_pack)
+	if (a_in_pack < b_in_pack)
 		return -1;
-	if (a->in_pack > b->in_pack)
+	if (a_in_pack > b_in_pack)
 		return 1;
 	return a->in_pack_offset < b->in_pack_offset ? -1 :
 			(a->in_pack_offset > b->in_pack_offset);
@@ -1563,31 +1597,37 @@ static int pack_offset_sort(const void *_a, const void *_b)
  */
 static void drop_reused_delta(struct object_entry *entry)
 {
-	struct object_entry **p = &entry->delta->delta_child;
+	unsigned *idx = &to_pack.objects[entry->delta_idx - 1].delta_child_idx;
 	struct object_info oi = OBJECT_INFO_INIT;
+	enum object_type type;
+	unsigned long size;
+
+	while (*idx) {
+		struct object_entry *oe = &to_pack.objects[*idx - 1];
 
-	while (*p) {
-		if (*p == entry)
-			*p = (*p)->delta_sibling;
+		if (oe == entry)
+			*idx = oe->delta_sibling_idx;
 		else
-			p = &(*p)->delta_sibling;
+			idx = &oe->delta_sibling_idx;
 	}
-	entry->delta = NULL;
+	SET_DELTA(entry, NULL);
 	entry->depth = 0;
 
-	oi.sizep = &entry->size;
-	oi.typep = &entry->type;
-	if (packed_object_info(the_repository, entry->in_pack,
-			       entry->in_pack_offset, &oi) < 0) {
+	oi.sizep = &size;
+	oi.typep = &type;
+	if (packed_object_info(the_repository, IN_PACK(entry), entry->in_pack_offset, &oi) < 0) {
 		/*
 		 * We failed to get the info from this pack for some reason;
 		 * fall back to sha1_object_info, which may find another copy.
-		 * And if that fails, the error will be recorded in entry->type
+		 * And if that fails, the error will be recorded in oe_type(entry)
 		 * and dealt with in prepare_pack().
 		 */
-		entry->type = oid_object_info(the_repository, &entry->idx.oid,
-					      &entry->size);
+		oe_set_type(entry,
+			    oid_object_info(the_repository, &entry->idx.oid, &size));
+	} else {
+		oe_set_type(entry, type);
 	}
+	SET_SIZE(entry, size);
 }
 
 /*
@@ -1611,7 +1651,7 @@ static void break_delta_chains(struct object_entry *entry)
 
 	for (cur = entry, total_depth = 0;
 	     cur;
-	     cur = cur->delta, total_depth++) {
+	     cur = DELTA(cur), total_depth++) {
 		if (cur->dfs_state == DFS_DONE) {
 			/*
 			 * We've already seen this object and know it isn't
@@ -1636,7 +1676,7 @@ static void break_delta_chains(struct object_entry *entry)
 		 * it's not a delta, we're done traversing, but we'll mark it
 		 * done to save time on future traversals.
 		 */
-		if (!cur->delta) {
+		if (!DELTA(cur)) {
 			cur->dfs_state = DFS_DONE;
 			break;
 		}
@@ -1659,7 +1699,7 @@ static void break_delta_chains(struct object_entry *entry)
 		 * We keep all commits in the chain that we examined.
 		 */
 		cur->dfs_state = DFS_ACTIVE;
-		if (cur->delta->dfs_state == DFS_ACTIVE) {
+		if (DELTA(cur)->dfs_state == DFS_ACTIVE) {
 			drop_reused_delta(cur);
 			cur->dfs_state = DFS_DONE;
 			break;
@@ -1674,7 +1714,7 @@ static void break_delta_chains(struct object_entry *entry)
 	 * an extra "next" pointer to keep going after we reset cur->delta.
 	 */
 	for (cur = entry; cur; cur = next) {
-		next = cur->delta;
+		next = DELTA(cur);
 
 		/*
 		 * We should have a chain of zero or more ACTIVE states down to
@@ -1731,7 +1771,8 @@ static void get_object_details(void)
 	for (i = 0; i < to_pack.nr_objects; i++) {
 		struct object_entry *entry = sorted_by_offset[i];
 		check_object(entry);
-		if (big_file_threshold < entry->size)
+		if (entry->type_valid &&
+		    oe_size_greater_than(&to_pack, entry, big_file_threshold))
 			entry->no_try_delta = 1;
 		display_progress(progress_state, i + 1);
 	}
@@ -1760,10 +1801,14 @@ static int type_size_sort(const void *_a, const void *_b)
 {
 	const struct object_entry *a = *(struct object_entry **)_a;
 	const struct object_entry *b = *(struct object_entry **)_b;
+	enum object_type a_type = oe_type(a);
+	enum object_type b_type = oe_type(b);
+	unsigned long a_size = SIZE(a);
+	unsigned long b_size = SIZE(b);
 
-	if (a->type > b->type)
+	if (a_type > b_type)
 		return -1;
-	if (a->type < b->type)
+	if (a_type < b_type)
 		return 1;
 	if (a->hash > b->hash)
 		return -1;
@@ -1773,9 +1818,9 @@ static int type_size_sort(const void *_a, const void *_b)
 		return -1;
 	if (a->preferred_base < b->preferred_base)
 		return 1;
-	if (a->size > b->size)
+	if (a_size > b_size)
 		return -1;
-	if (a->size < b->size)
+	if (a_size < b_size)
 		return 1;
 	return a < b ? -1 : (a > b);  /* newest first */
 }
@@ -1828,6 +1873,46 @@ static pthread_mutex_t progress_mutex;
 
 #endif
 
+/*
+ * Return the size of the object without doing any delta
+ * reconstruction (so non-deltas are true object sizes, but deltas
+ * return the size of the delta data).
+ */
+unsigned long oe_get_size_slow(struct packing_data *pack,
+			       const struct object_entry *e)
+{
+	struct packed_git *p;
+	struct pack_window *w_curs;
+	unsigned char *buf;
+	enum object_type type;
+	unsigned long used, avail, size;
+
+	if (e->type_ != OBJ_OFS_DELTA && e->type_ != OBJ_REF_DELTA) {
+		read_lock();
+		if (oid_object_info(the_repository, &e->idx.oid, &size) < 0)
+			die(_("unable to get size of %s"),
+			    oid_to_hex(&e->idx.oid));
+		read_unlock();
+		return size;
+	}
+
+	p = oe_in_pack(pack, e);
+	if (!p)
+		BUG("when e->type is a delta, it must belong to a pack");
+
+	read_lock();
+	w_curs = NULL;
+	buf = use_pack(p, &w_curs, e->in_pack_offset, &avail);
+	used = unpack_object_header_buffer(buf, avail, &type, &size);
+	if (used == 0)
+		die(_("unable to parse object header of %s"),
+		    oid_to_hex(&e->idx.oid));
+
+	unuse_pack(&w_curs);
+	read_unlock();
+	return size;
+}
+
 static int try_delta(struct unpacked *trg, struct unpacked *src,
 		     unsigned max_depth, unsigned long *mem_usage)
 {
@@ -1839,7 +1924,7 @@ static int try_delta(struct unpacked *trg, struct unpacked *src,
 	void *delta_buf;
 
 	/* Don't bother doing diffs between different types */
-	if (trg_entry->type != src_entry->type)
+	if (oe_type(trg_entry) != oe_type(src_entry))
 		return -1;
 
 	/*
@@ -1850,8 +1935,8 @@ static int try_delta(struct unpacked *trg, struct unpacked *src,
 	 * it, we will still save the transfer cost, as we already know
 	 * the other side has it and we won't send src_entry at all.
 	 */
-	if (reuse_delta && trg_entry->in_pack &&
-	    trg_entry->in_pack == src_entry->in_pack &&
+	if (reuse_delta && IN_PACK(trg_entry) &&
+	    IN_PACK(trg_entry) == IN_PACK(src_entry) &&
 	    !src_entry->preferred_base &&
 	    trg_entry->in_pack_type != OBJ_REF_DELTA &&
 	    trg_entry->in_pack_type != OBJ_OFS_DELTA)
@@ -1862,19 +1947,19 @@ static int try_delta(struct unpacked *trg, struct unpacked *src,
 		return 0;
 
 	/* Now some size filtering heuristics. */
-	trg_size = trg_entry->size;
-	if (!trg_entry->delta) {
+	trg_size = SIZE(trg_entry);
+	if (!DELTA(trg_entry)) {
 		max_size = trg_size/2 - 20;
 		ref_depth = 1;
 	} else {
-		max_size = trg_entry->delta_size;
+		max_size = DELTA_SIZE(trg_entry);
 		ref_depth = trg->depth;
 	}
 	max_size = (uint64_t)max_size * (max_depth - src->depth) /
 						(max_depth - ref_depth + 1);
 	if (max_size == 0)
 		return 0;
-	src_size = src_entry->size;
+	src_size = SIZE(src_entry);
 	sizediff = src_size < trg_size ? trg_size - src_size : 0;
 	if (sizediff >= max_size)
 		return 0;
@@ -1936,10 +2021,14 @@ static int try_delta(struct unpacked *trg, struct unpacked *src,
 	delta_buf = create_delta(src->index, trg->data, trg_size, &delta_size, max_size);
 	if (!delta_buf)
 		return 0;
+	if (delta_size >= (1U << OE_DELTA_SIZE_BITS)) {
+		free(delta_buf);
+		return 0;
+	}
 
-	if (trg_entry->delta) {
+	if (DELTA(trg_entry)) {
 		/* Prefer only shallower same-sized deltas. */
-		if (delta_size == trg_entry->delta_size &&
+		if (delta_size == DELTA_SIZE(trg_entry) &&
 		    src->depth + 1 >= trg->depth) {
 			free(delta_buf);
 			return 0;
@@ -1954,7 +2043,7 @@ static int try_delta(struct unpacked *trg, struct unpacked *src,
 	free(trg_entry->delta_data);
 	cache_lock();
 	if (trg_entry->delta_data) {
-		delta_cache_size -= trg_entry->delta_size;
+		delta_cache_size -= DELTA_SIZE(trg_entry);
 		trg_entry->delta_data = NULL;
 	}
 	if (delta_cacheable(src_size, trg_size, delta_size)) {
@@ -1966,8 +2055,8 @@ static int try_delta(struct unpacked *trg, struct unpacked *src,
 		free(delta_buf);
 	}
 
-	trg_entry->delta = src_entry;
-	trg_entry->delta_size = delta_size;
+	SET_DELTA(trg_entry, src_entry);
+	SET_DELTA_SIZE(trg_entry, delta_size);
 	trg->depth = src->depth + 1;
 
 	return 1;
@@ -1975,13 +2064,13 @@ static int try_delta(struct unpacked *trg, struct unpacked *src,
 
 static unsigned int check_delta_limit(struct object_entry *me, unsigned int n)
 {
-	struct object_entry *child = me->delta_child;
+	struct object_entry *child = DELTA_CHILD(me);
 	unsigned int m = n;
 	while (child) {
 		unsigned int c = check_delta_limit(child, n + 1);
 		if (m < c)
 			m = c;
-		child = child->delta_sibling;
+		child = DELTA_SIBLING(child);
 	}
 	return m;
 }
@@ -1992,7 +2081,7 @@ static unsigned long free_unpacked(struct unpacked *n)
 	free_delta_index(n->index);
 	n->index = NULL;
 	if (n->data) {
-		freed_mem += n->entry->size;
+		freed_mem += SIZE(n->entry);
 		FREE_AND_NULL(n->data);
 	}
 	n->entry = NULL;
@@ -2050,7 +2139,7 @@ static void find_deltas(struct object_entry **list, unsigned *list_size,
 		 * otherwise they would become too deep.
 		 */
 		max_depth = depth;
-		if (entry->delta_child) {
+		if (DELTA_CHILD(entry)) {
 			max_depth -= check_delta_limit(entry, 0);
 			if (max_depth <= 0)
 				goto next;
@@ -2088,19 +2177,26 @@ static void find_deltas(struct object_entry **list, unsigned *list_size,
 		 * between writes at that moment.
 		 */
 		if (entry->delta_data && !pack_to_stdout) {
-			entry->z_delta_size = do_compress(&entry->delta_data,
-							  entry->delta_size);
-			cache_lock();
-			delta_cache_size -= entry->delta_size;
-			delta_cache_size += entry->z_delta_size;
-			cache_unlock();
+			unsigned long size;
+
+			size = do_compress(&entry->delta_data, DELTA_SIZE(entry));
+			if (size < (1U << OE_Z_DELTA_BITS)) {
+				entry->z_delta_size = size;
+				cache_lock();
+				delta_cache_size -= DELTA_SIZE(entry);
+				delta_cache_size += entry->z_delta_size;
+				cache_unlock();
+			} else {
+				FREE_AND_NULL(entry->delta_data);
+				entry->z_delta_size = 0;
+			}
 		}
 
 		/* if we made n a delta, and if n is already at max
 		 * depth, leaving it in the window is pointless.  we
 		 * should evict it first.
 		 */
-		if (entry->delta && max_depth <= n->depth)
+		if (DELTA(entry) && max_depth <= n->depth)
 			continue;
 
 		/*
@@ -2108,7 +2204,7 @@ static void find_deltas(struct object_entry **list, unsigned *list_size,
 		 * currently deltified object, to keep it longer.  It will
 		 * be the first base object to be attempted next.
 		 */
-		if (entry->delta) {
+		if (DELTA(entry)) {
 			struct unpacked swap = array[best_base];
 			int dist = (window + idx - best_base) % window;
 			int dst = best_base;
@@ -2429,13 +2525,14 @@ static void prepare_pack(int window, int depth)
 	for (i = 0; i < to_pack.nr_objects; i++) {
 		struct object_entry *entry = to_pack.objects + i;
 
-		if (entry->delta)
+		if (DELTA(entry))
 			/* This happens if we decided to reuse existing
 			 * delta from a pack.  "reuse_delta &&" is implied.
 			 */
 			continue;
 
-		if (entry->size < 50)
+		if (!entry->type_valid ||
+		    oe_size_less_than(&to_pack, entry, 50))
 			continue;
 
 		if (entry->no_try_delta)
@@ -2443,11 +2540,11 @@ static void prepare_pack(int window, int depth)
 
 		if (!entry->preferred_base) {
 			nr_deltas++;
-			if (entry->type < 0)
+			if (oe_type(entry) < 0)
 				die("unable to get type of object %s",
 				    oid_to_hex(&entry->idx.oid));
 		} else {
-			if (entry->type < 0) {
+			if (oe_type(entry) < 0) {
 				/*
 				 * This object is not found, but we
 				 * don't have to include it anyway.
@@ -2556,7 +2653,7 @@ static void read_object_list_from_stdin(void)
 			die("expected object ID, got garbage:\n %s", line);
 
 		add_preferred_base_object(p + 1);
-		add_object_entry(&oid, 0, p + 1, 0);
+		add_object_entry(&oid, OBJ_NONE, p + 1, 0);
 	}
 }
 
@@ -3083,6 +3180,9 @@ int cmd_pack_objects(int argc, const char **argv, const char *prefix)
 		OPT_END(),
 	};
 
+	if (DFS_NUM_STATES > (1 << OE_DFS_STATE_BITS))
+		BUG("too many dfs states, increase OE_DFS_STATE_BITS");
+
 	check_replace_refs = 0;
 
 	reset_pack_idx_option(&pack_idx_opts);
@@ -3099,6 +3199,17 @@ int cmd_pack_objects(int argc, const char **argv, const char *prefix)
 	if (pack_to_stdout != !base_name || argc)
 		usage_with_options(pack_usage, pack_objects_options);
 
+	if (depth >= (1 << OE_DEPTH_BITS)) {
+		warning(_("delta chain depth %d is too deep, forcing %d"),
+			depth, (1 << OE_DEPTH_BITS) - 1);
+		depth = (1 << OE_DEPTH_BITS) - 1;
+	}
+	if (cache_max_small_delta_size >= (1U << OE_Z_DELTA_BITS)) {
+		warning(_("pack.deltaCacheLimit is too high, forcing %d"),
+			(1U << OE_Z_DELTA_BITS) - 1);
+		cache_max_small_delta_size = (1U << OE_Z_DELTA_BITS) - 1;
+	}
+
 	argv_array_push(&rp, "pack-objects");
 	if (thin) {
 		use_internal_rev_list = 1;
@@ -3217,6 +3328,8 @@ int cmd_pack_objects(int argc, const char **argv, const char *prefix)
 		}
 	}
 
+	prepare_packing_data(&to_pack);
+
 	if (progress)
 		progress_state = start_progress(_("Enumerating objects"), 0);
 	if (!use_internal_rev_list)
diff --git a/cache.h b/cache.h
index f436744363..6dedf3c4f9 100644
--- a/cache.h
+++ b/cache.h
@@ -373,6 +373,8 @@ extern void free_name_hash(struct index_state *istate);
 #define read_blob_data_from_cache(path, sz) read_blob_data_from_index(&the_index, (path), (sz))
 #endif
 
+#define TYPE_BITS 3
+
 /*
  * Values in this enum (except those outside the 3 bit range) are part
  * of pack file format. See Documentation/technical/pack-format.txt
diff --git a/ci/run-build-and-tests.sh b/ci/run-build-and-tests.sh
index 3735ce413f..4b04c75b7f 100755
--- a/ci/run-build-and-tests.sh
+++ b/ci/run-build-and-tests.sh
@@ -11,7 +11,10 @@ make --jobs=2
 make --quiet test
 if test "$jobname" = "linux-gcc"
 then
-	GIT_TEST_SPLIT_INDEX=YesPlease make --quiet test
+	export GIT_TEST_SPLIT_INDEX=yes
+	export GIT_TEST_FULL_IN_PACK_ARRAY=true
+	export GIT_TEST_OE_SIZE=10
+	make --quiet test
 fi
 
 check_unignored_build_artifacts
diff --git a/object-store.h b/object-store.h
index 485b819f00..d683112fd7 100644
--- a/object-store.h
+++ b/object-store.h
@@ -71,6 +71,7 @@ struct packed_git {
 	int index_version;
 	time_t mtime;
 	int pack_fd;
+	int index;              /* for builtin/pack-objects.c */
 	unsigned pack_local:1,
 		 pack_keep:1,
 		 pack_keep_in_core:1,
diff --git a/object.h b/object.h
index b8e70e5519..5c13955000 100644
--- a/object.h
+++ b/object.h
@@ -25,7 +25,6 @@ struct object_array {
 
 #define OBJECT_ARRAY_INIT { 0, 0, NULL }
 
-#define TYPE_BITS   3
 /*
  * object flag allocation:
  * revision.h:               0---------10                                26
diff --git a/pack-bitmap-write.c b/pack-bitmap-write.c
index f202b64911..72d9daec7e 100644
--- a/pack-bitmap-write.c
+++ b/pack-bitmap-write.c
@@ -48,7 +48,8 @@ void bitmap_writer_show_progress(int show)
 /**
  * Build the initial type index for the packfile
  */
-void bitmap_writer_build_type_index(struct pack_idx_entry **index,
+void bitmap_writer_build_type_index(struct packing_data *to_pack,
+				    struct pack_idx_entry **index,
 				    uint32_t index_nr)
 {
 	uint32_t i;
@@ -57,19 +58,20 @@ void bitmap_writer_build_type_index(struct pack_idx_entry **index,
 	writer.trees = ewah_new();
 	writer.blobs = ewah_new();
 	writer.tags = ewah_new();
+	ALLOC_ARRAY(to_pack->in_pack_pos, to_pack->nr_objects);
 
 	for (i = 0; i < index_nr; ++i) {
 		struct object_entry *entry = (struct object_entry *)index[i];
 		enum object_type real_type;
 
-		entry->in_pack_pos = i;
+		oe_set_in_pack_pos(to_pack, entry, i);
 
-		switch (entry->type) {
+		switch (oe_type(entry)) {
 		case OBJ_COMMIT:
 		case OBJ_TREE:
 		case OBJ_BLOB:
 		case OBJ_TAG:
-			real_type = entry->type;
+			real_type = oe_type(entry);
 			break;
 
 		default:
@@ -98,7 +100,7 @@ void bitmap_writer_build_type_index(struct pack_idx_entry **index,
 		default:
 			die("Missing type information for %s (%d/%d)",
 			    oid_to_hex(&entry->idx.oid), real_type,
-			    entry->type);
+			    oe_type(entry));
 		}
 	}
 }
@@ -147,7 +149,7 @@ static uint32_t find_object_pos(const unsigned char *sha1)
 			"(object %s is missing)", sha1_to_hex(sha1));
 	}
 
-	return entry->in_pack_pos;
+	return oe_in_pack_pos(writer.to_pack, entry);
 }
 
 static void show_object(struct object *object, const char *name, void *data)
diff --git a/pack-bitmap.c b/pack-bitmap.c
index 3f2dab340f..c9e90d1bb5 100644
--- a/pack-bitmap.c
+++ b/pack-bitmap.c
@@ -1033,7 +1033,7 @@ int rebuild_existing_bitmaps(struct packing_data *mapping,
 		oe = packlist_find(mapping, sha1, NULL);
 
 		if (oe)
-			reposition[i] = oe->in_pack_pos + 1;
+			reposition[i] = oe_in_pack_pos(mapping, oe) + 1;
 	}
 
 	rebuild = bitmap_new();
diff --git a/pack-bitmap.h b/pack-bitmap.h
index 3742a00e14..5ded2f139a 100644
--- a/pack-bitmap.h
+++ b/pack-bitmap.h
@@ -44,7 +44,9 @@ int rebuild_existing_bitmaps(struct packing_data *mapping, khash_sha1 *reused_bi
 
 void bitmap_writer_show_progress(int show);
 void bitmap_writer_set_checksum(unsigned char *sha1);
-void bitmap_writer_build_type_index(struct pack_idx_entry **index, uint32_t index_nr);
+void bitmap_writer_build_type_index(struct packing_data *to_pack,
+				    struct pack_idx_entry **index,
+				    uint32_t index_nr);
 void bitmap_writer_reuse_bitmaps(struct packing_data *to_pack);
 void bitmap_writer_select_commits(struct commit **indexed_commits,
 		unsigned int indexed_commits_nr, int max_bitmaps);
diff --git a/pack-objects.c b/pack-objects.c
index 9558d13834..e0c4600568 100644
--- a/pack-objects.c
+++ b/pack-objects.c
@@ -2,6 +2,8 @@
 #include "object.h"
 #include "pack.h"
 #include "pack-objects.h"
+#include "packfile.h"
+#include "config.h"
 
 static uint32_t locate_object_entry_hash(struct packing_data *pdata,
 					 const unsigned char *sha1,
@@ -86,6 +88,66 @@ struct object_entry *packlist_find(struct packing_data *pdata,
 	return &pdata->objects[pdata->index[i] - 1];
 }
 
+static void prepare_in_pack_by_idx(struct packing_data *pdata)
+{
+	struct packed_git **mapping, *p;
+	int cnt = 0, nr = 1U << OE_IN_PACK_BITS;
+
+	ALLOC_ARRAY(mapping, nr);
+	/*
+	 * oe_in_pack() on an all-zero'd object_entry
+	 * (i.e. in_pack_idx also zero) should return NULL.
+	 */
+	mapping[cnt++] = NULL;
+	for (p = get_packed_git(the_repository); p; p = p->next, cnt++) {
+		if (cnt == nr) {
+			free(mapping);
+			return;
+		}
+		p->index = cnt;
+		mapping[cnt] = p;
+	}
+	pdata->in_pack_by_idx = mapping;
+}
+
+/*
+ * A new pack appears after prepare_in_pack_by_idx() has been
+ * run. This is likely a race.
+ *
+ * We could map this new pack to in_pack_by_idx[] array, but then we
+ * have to deal with full array anyway. And since it's hard to test
+ * this fall back code, just stay simple and fall back to using
+ * in_pack[] array.
+ */
+void oe_map_new_pack(struct packing_data *pack,
+		     struct packed_git *p)
+{
+	uint32_t i;
+
+	REALLOC_ARRAY(pack->in_pack, pack->nr_alloc);
+
+	for (i = 0; i < pack->nr_objects; i++)
+		pack->in_pack[i] = oe_in_pack(pack, pack->objects + i);
+
+	FREE_AND_NULL(pack->in_pack_by_idx);
+}
+
+/* assume pdata is already zero'd by caller */
+void prepare_packing_data(struct packing_data *pdata)
+{
+	if (git_env_bool("GIT_TEST_FULL_IN_PACK_ARRAY", 0)) {
+		/*
+		 * do not initialize in_pack_by_idx[] to force the
+		 * slow path in oe_in_pack()
+		 */
+	} else {
+		prepare_in_pack_by_idx(pdata);
+	}
+
+	pdata->oe_size_limit = git_env_ulong("GIT_TEST_OE_SIZE",
+					     1U << OE_SIZE_BITS);
+}
+
 struct object_entry *packlist_alloc(struct packing_data *pdata,
 				    const unsigned char *sha1,
 				    uint32_t index_pos)
@@ -95,6 +157,9 @@ struct object_entry *packlist_alloc(struct packing_data *pdata,
 	if (pdata->nr_objects >= pdata->nr_alloc) {
 		pdata->nr_alloc = (pdata->nr_alloc  + 1024) * 3 / 2;
 		REALLOC_ARRAY(pdata->objects, pdata->nr_alloc);
+
+		if (!pdata->in_pack_by_idx)
+			REALLOC_ARRAY(pdata->in_pack, pdata->nr_alloc);
 	}
 
 	new_entry = pdata->objects + pdata->nr_objects++;
@@ -107,5 +172,8 @@ struct object_entry *packlist_alloc(struct packing_data *pdata,
 	else
 		pdata->index[index_pos] = pdata->nr_objects;
 
+	if (pdata->in_pack)
+		pdata->in_pack[pdata->nr_objects - 1] = NULL;
+
 	return new_entry;
 }
diff --git a/pack-objects.h b/pack-objects.h
index af4f46c026..edf74dabdd 100644
--- a/pack-objects.h
+++ b/pack-objects.h
@@ -1,47 +1,125 @@
 #ifndef PACK_OBJECTS_H
 #define PACK_OBJECTS_H
 
+#include "object-store.h"
+
 #define DEFAULT_DELTA_CACHE_SIZE (256 * 1024 * 1024)
 
+#define OE_DFS_STATE_BITS	2
+#define OE_DEPTH_BITS		12
+#define OE_IN_PACK_BITS		10
+#define OE_Z_DELTA_BITS		20
+/*
+ * Note that oe_set_size() becomes expensive when the given size is
+ * above this limit. Don't lower it too much.
+ */
+#define OE_SIZE_BITS		31
+#define OE_DELTA_SIZE_BITS	20
+
+/*
+ * State flags for depth-first search used for analyzing delta cycles.
+ *
+ * The depth is measured in delta-links to the base (so if A is a delta
+ * against B, then A has a depth of 1, and B a depth of 0).
+ */
+enum dfs_state {
+	DFS_NONE = 0,
+	DFS_ACTIVE,
+	DFS_DONE,
+	DFS_NUM_STATES
+};
+
+/*
+ * The size of struct nearly determines pack-objects's memory
+ * consumption. This struct is packed tight for that reason. When you
+ * add or reorder something in this struct, think a bit about this.
+ *
+ * basic object info
+ * -----------------
+ * idx.oid is filled up before delta searching starts. idx.crc32 is
+ * only valid after the object is written out and will be used for
+ * generating the index. idx.offset will be both gradually set and
+ * used in writing phase (base objects get offset first, then deltas
+ * refer to them)
+ *
+ * "size" is the uncompressed object size. Compressed size of the raw
+ * data for an object in a pack is not stored anywhere but is computed
+ * and made available when reverse .idx is made. Note that when a
+ * delta is reused, "size" is the uncompressed _delta_ size, not the
+ * canonical one after the delta has been applied.
+ *
+ * "hash" contains a path name hash which is used for sorting the
+ * delta list and also during delta searching. Once prepare_pack()
+ * returns it's no longer needed.
+ *
+ * source pack info
+ * ----------------
+ * The (in_pack, in_pack_offset) tuple contains the location of the
+ * object in the source pack. in_pack_header_size allows quickly
+ * skipping the header and going straight to the zlib stream.
+ *
+ * "type" and "in_pack_type" both describe object type. in_pack_type
+ * may contain a delta type, while type is always the canonical type.
+ *
+ * deltas
+ * ------
+ * Delta links (delta, delta_child and delta_sibling) are created to
+ * reflect that delta graph from the source pack then updated or added
+ * during delta searching phase when we find better deltas.
+ *
+ * delta_child and delta_sibling are last needed in
+ * compute_write_order(). "delta" and "delta_size" must remain valid
+ * at object writing phase in case the delta is not cached.
+ *
+ * If a delta is cached in memory and is compressed, delta_data points
+ * to the data and z_delta_size contains the compressed size. If it's
+ * uncompressed [1], z_delta_size must be zero. delta_size is always
+ * the uncompressed size and must be valid even if the delta is not
+ * cached.
+ *
+ * [1] during try_delta phase we don't bother with compressing because
+ * the delta could be quickly replaced with a better one.
+ */
 struct object_entry {
 	struct pack_idx_entry idx;
-	unsigned long size;	/* uncompressed size */
-	struct packed_git *in_pack;	/* already in pack */
-	off_t in_pack_offset;
-	struct object_entry *delta;	/* delta base object */
-	struct object_entry *delta_child; /* deltified objects who bases me */
-	struct object_entry *delta_sibling; /* other deltified objects who
-					     * uses the same base as me
-					     */
 	void *delta_data;	/* cached delta (uncompressed) */
-	unsigned long delta_size;	/* delta data size (uncompressed) */
-	unsigned long z_delta_size;	/* delta data size (compressed) */
-	enum object_type type;
-	enum object_type in_pack_type;	/* could be delta */
+	off_t in_pack_offset;
 	uint32_t hash;			/* name hint hash */
-	unsigned int in_pack_pos;
-	unsigned char in_pack_header_size;
+	unsigned size_:OE_SIZE_BITS;
+	unsigned size_valid:1;
+	uint32_t delta_idx;	/* delta base object */
+	uint32_t delta_child_idx; /* deltified objects who bases me */
+	uint32_t delta_sibling_idx; /* other deltified objects who
+				     * uses the same base as me
+				     */
+	unsigned delta_size_:OE_DELTA_SIZE_BITS; /* delta data size (uncompressed) */
+	unsigned delta_size_valid:1;
+	unsigned in_pack_idx:OE_IN_PACK_BITS;	/* already in pack */
+	unsigned z_delta_size:OE_Z_DELTA_BITS;
+	unsigned type_valid:1;
+	unsigned type_:TYPE_BITS;
+	unsigned no_try_delta:1;
+	unsigned in_pack_type:TYPE_BITS; /* could be delta */
 	unsigned preferred_base:1; /*
 				    * we do not pack this, but is available
 				    * to be used as the base object to delta
 				    * objects against.
 				    */
-	unsigned no_try_delta:1;
 	unsigned tagged:1; /* near the very tip of refs */
 	unsigned filled:1; /* assigned write-order */
+	unsigned dfs_state:OE_DFS_STATE_BITS;
+	unsigned char in_pack_header_size;
+	unsigned depth:OE_DEPTH_BITS;
 
 	/*
-	 * State flags for depth-first search used for analyzing delta cycles.
+	 * pahole results on 64-bit linux (gcc and clang)
 	 *
-	 * The depth is measured in delta-links to the base (so if A is a delta
-	 * against B, then A has a depth of 1, and B a depth of 0).
+	 *   size: 80, bit_padding: 20 bits, holes: 8 bits
+	 *
+	 * and on 32-bit (gcc)
+	 *
+	 *   size: 76, bit_padding: 20 bits, holes: 8 bits
 	 */
-	enum {
-		DFS_NONE = 0,
-		DFS_ACTIVE,
-		DFS_DONE
-	} dfs_state;
-	int depth;
 };
 
 struct packing_data {
@@ -50,8 +128,22 @@ struct packing_data {
 
 	int32_t *index;
 	uint32_t index_size;
+
+	unsigned int *in_pack_pos;
+
+	/*
+	 * Only one of these can be non-NULL and they have different
+	 * sizes. if in_pack_by_idx is allocated, oe_in_pack() returns
+	 * the pack of an object using in_pack_idx field. If not,
+	 * in_pack[] array is used the same way as in_pack_pos[]
+	 */
+	struct packed_git **in_pack_by_idx;
+	struct packed_git **in_pack;
+
+	uintmax_t oe_size_limit;
 };
 
+void prepare_packing_data(struct packing_data *pdata);
 struct object_entry *packlist_alloc(struct packing_data *pdata,
 				    const unsigned char *sha1,
 				    uint32_t index_pos);
@@ -80,4 +172,178 @@ static inline uint32_t pack_name_hash(const char *name)
 	return hash;
 }
 
+static inline enum object_type oe_type(const struct object_entry *e)
+{
+	return e->type_valid ? e->type_ : OBJ_BAD;
+}
+
+static inline void oe_set_type(struct object_entry *e,
+			       enum object_type type)
+{
+	if (type >= OBJ_ANY)
+		BUG("OBJ_ANY cannot be set in pack-objects code");
+
+	e->type_valid = type >= OBJ_NONE;
+	e->type_ = (unsigned)type;
+}
+
+static inline unsigned int oe_in_pack_pos(const struct packing_data *pack,
+					  const struct object_entry *e)
+{
+	return pack->in_pack_pos[e - pack->objects];
+}
+
+static inline void oe_set_in_pack_pos(const struct packing_data *pack,
+				      const struct object_entry *e,
+				      unsigned int pos)
+{
+	pack->in_pack_pos[e - pack->objects] = pos;
+}
+
+static inline struct packed_git *oe_in_pack(const struct packing_data *pack,
+					    const struct object_entry *e)
+{
+	if (pack->in_pack_by_idx)
+		return pack->in_pack_by_idx[e->in_pack_idx];
+	else
+		return pack->in_pack[e - pack->objects];
+}
+
+void oe_map_new_pack(struct packing_data *pack,
+		     struct packed_git *p);
+static inline void oe_set_in_pack(struct packing_data *pack,
+				  struct object_entry *e,
+				  struct packed_git *p)
+{
+	if (!p->index)
+		oe_map_new_pack(pack, p);
+	if (pack->in_pack_by_idx)
+		e->in_pack_idx = p->index;
+	else
+		pack->in_pack[e - pack->objects] = p;
+}
+
+static inline struct object_entry *oe_delta(
+		const struct packing_data *pack,
+		const struct object_entry *e)
+{
+	if (e->delta_idx)
+		return &pack->objects[e->delta_idx - 1];
+	return NULL;
+}
+
+static inline void oe_set_delta(struct packing_data *pack,
+				struct object_entry *e,
+				struct object_entry *delta)
+{
+	if (delta)
+		e->delta_idx = (delta - pack->objects) + 1;
+	else
+		e->delta_idx = 0;
+}
+
+static inline struct object_entry *oe_delta_child(
+		const struct packing_data *pack,
+		const struct object_entry *e)
+{
+	if (e->delta_child_idx)
+		return &pack->objects[e->delta_child_idx - 1];
+	return NULL;
+}
+
+static inline void oe_set_delta_child(struct packing_data *pack,
+				      struct object_entry *e,
+				      struct object_entry *delta)
+{
+	if (delta)
+		e->delta_child_idx = (delta - pack->objects) + 1;
+	else
+		e->delta_child_idx = 0;
+}
+
+static inline struct object_entry *oe_delta_sibling(
+		const struct packing_data *pack,
+		const struct object_entry *e)
+{
+	if (e->delta_sibling_idx)
+		return &pack->objects[e->delta_sibling_idx - 1];
+	return NULL;
+}
+
+static inline void oe_set_delta_sibling(struct packing_data *pack,
+					struct object_entry *e,
+					struct object_entry *delta)
+{
+	if (delta)
+		e->delta_sibling_idx = (delta - pack->objects) + 1;
+	else
+		e->delta_sibling_idx = 0;
+}
+
+unsigned long oe_get_size_slow(struct packing_data *pack,
+			       const struct object_entry *e);
+static inline unsigned long oe_size(struct packing_data *pack,
+				    const struct object_entry *e)
+{
+	if (e->size_valid)
+		return e->size_;
+
+	return oe_get_size_slow(pack, e);
+}
+
+static inline int oe_size_less_than(struct packing_data *pack,
+				    const struct object_entry *lhs,
+				    unsigned long rhs)
+{
+	if (lhs->size_valid)
+		return lhs->size_ < rhs;
+	if (rhs < pack->oe_size_limit) /* rhs < 2^x <= lhs ? */
+		return 0;
+	return oe_get_size_slow(pack, lhs) < rhs;
+}
+
+static inline int oe_size_greater_than(struct packing_data *pack,
+				       const struct object_entry *lhs,
+				       unsigned long rhs)
+{
+	if (lhs->size_valid)
+		return lhs->size_ > rhs;
+	if (rhs < pack->oe_size_limit) /* rhs < 2^x <= lhs ? */
+		return 1;
+	return oe_get_size_slow(pack, lhs) > rhs;
+}
+
+static inline void oe_set_size(struct packing_data *pack,
+			       struct object_entry *e,
+			       unsigned long size)
+{
+	if (size < pack->oe_size_limit) {
+		e->size_ = size;
+		e->size_valid = 1;
+	} else {
+		e->size_valid = 0;
+		if (oe_get_size_slow(pack, e) != size)
+			BUG("'size' is supposed to be the object size!");
+	}
+}
+
+static inline unsigned long oe_delta_size(struct packing_data *pack,
+					  const struct object_entry *e)
+{
+	if (e->delta_size_valid)
+		return e->delta_size_;
+	return oe_size(pack, e);
+}
+
+static inline void oe_set_delta_size(struct packing_data *pack,
+				     struct object_entry *e,
+				     unsigned long size)
+{
+	e->delta_size_ = size;
+	e->delta_size_valid = e->delta_size_ == size;
+	if (!e->delta_size_valid && size != oe_size(pack, e))
+		BUG("this can only happen in check_object() "
+		    "where delta size is the same as entry size");
+}
+
 #endif
diff --git a/read-cache.c b/read-cache.c
index 10f1c6bb8a..fa3df2e72e 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -2268,7 +2268,7 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile,
 
 	if (!istate->version) {
 		istate->version = get_index_format_default();
-		if (getenv("GIT_TEST_SPLIT_INDEX"))
+		if (git_env_bool("GIT_TEST_SPLIT_INDEX", 0))
 			init_split_index(istate);
 	}
 
@@ -2559,7 +2559,7 @@ int write_locked_index(struct index_state *istate, struct lock_file *lock,
 		goto out;
 	}
 
-	if (getenv("GIT_TEST_SPLIT_INDEX")) {
+	if (git_env_bool("GIT_TEST_SPLIT_INDEX", 0)) {
 		int v = si->base_sha1[0];
 		if ((v & 15) < 6)
 			istate->cache_changed |= SPLIT_INDEX_ORDERED;
diff --git a/t/README b/t/README
index 24ddebfabf..8373a27fea 100644
--- a/t/README
+++ b/t/README
@@ -293,6 +293,28 @@ and know what setup is needed for it.  Or when you want to run
 everything up to a certain test.
 
 
+Running tests with special setups
+---------------------------------
+
+The whole test suite could be run to test some special features
+that cannot be easily covered by a few specific test cases. These
+could be enabled by running the test suite with correct GIT_TEST_
+environment set.
+
+GIT_TEST_SPLIT_INDEX=<boolean> forces split-index mode on the whole
+test suite. Accept any boolean values that are accepted by git-config.
+
+GIT_TEST_FULL_IN_PACK_ARRAY=<boolean> exercises the uncommon
+pack-objects code path where there are more than 1024 packs even if
+the actual number of packs in repository is below this limit. Accept
+any boolean values that are accepted by git-config.
+
+GIT_TEST_OE_SIZE=<n> exercises the uncommon pack-objects code path
+where we do not cache object size in memory and read it from existing
+packs on demand. This normally only happens when the object size is
+over 2GB. This variable forces the code path on any object larger than
+<n> bytes.
+
 Naming Tests
 ------------
 
diff --git a/t/t5300-pack-object.sh b/t/t5300-pack-object.sh
index 65ff60f2ee..54eff03851 100755
--- a/t/t5300-pack-object.sh
+++ b/t/t5300-pack-object.sh
@@ -457,6 +457,11 @@ test_expect_success !PTHREADS,C_LOCALE_OUTPUT 'pack-objects --threads=N or pack.
 	grep -F "no threads support, ignoring pack.threads" err
 '
 
+test_expect_success 'pack-objects in too-many-packs mode' '
+	GIT_TEST_FULL_IN_PACK_ARRAY=1 git repack -ad &&
+	git fsck
+'
+
 #
 # WARNING!
 #