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

Author: gitster

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

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`;

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`.