[PATCH 00/11] Reduce pack-objects memory footprint

The array of object_entry in pack-objects can take a lot of memory when pack-objects is run in "pack everything" mode. On linux-2.6.git, this array alone takes roughly 800MB.

This series reorders some fields and reduces field size... to keep this struct smaller. Its size goes from 136 bytes to 96 bytes (29%) on 64-bit linux and saves 260MB on linux-2.6.git.

Now the bad side:

- the number of pack files pack-objects can handle is reduced to 4096
  (previously unlimited)
- max delta chain is also limited to 4096 (previously practically
  unlimited)
- some patches are quite invasive (e.g. replacing pointer with
  uint32_t) and reduces readability a bit.
- it may be tricker to add more data in object_entry in the future.

Nguyễn Thái Ngọc Duy (11):
  pack-objects: document holes in struct object_entry.h
  pack-objects: turn type and in_pack_type to bitfields
  pack-objects: use bitfield for object_entry::dfs_state
  pack-objects: use bitfield for object_entry::depth
  pack-objects: note about in_pack_header_size
  pack-objects: move in_pack_pos out of struct object_entry
  pack-objects: move in_pack out of struct object_entry
  pack-objects: faster reverse packed_git lookup
  pack-objects: refer to delta objects by index instead of pointer
  pack-objects: reorder 'hash' to pack struct object_entry
  pack-objects: increase pack file limit to 4096

 builtin/pack-objects.c | 189 ++++++++++++++++++++++++++---------------
 cache.h                |   3 +
 object.h               |   1 -
 pack-bitmap-write.c    |   8 +-
 pack-bitmap.c          |   2 +-
 pack-bitmap.h          |   4 +-
 pack-objects.h         |  70 ++++++++++-----
 7 files changed, 180 insertions(+), 97 deletions(-)