[PATCH 14/15] pack-objects: reorder members to shrink struct object_entry
- From
Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
- Date
- Apr 14, 2018, 15:35 UTC
- Message-ID
- <20180414153513.9902-15-pclouds@gmail.com>
- In-Reply-To
- <20180414153513.9902-1-pclouds@gmail.com>
Previous patches leave lots of holes and padding in this struct. This patch reorders the members and shrinks the struct down to 80 bytes (from 136 bytes on 64-bit systems, before any field shrinking is done) with 16 bits to spare (and a couple more in in_pack_header_size when we really run out of bits).
This is the last in a series of memory reduction patches (see "pack-objects: a bit of document about struct object_entry" for the first one).
Overall they've reduced repack memory size on linux-2.6.git from 3.747G to 3.424G, or by around 320M, a decrease of 8.5%. The runtime of repack has stayed the same throughout this series. Ævar's testing on a big monorepo he has access to (bigger than linux-2.6.git) has shown a 7.9% reduction, so the overall expected improvement should be somewhere around 8%.
See 87po42cwql.fsf@evledraar.gmail.com on-list (https://public-inbox.org/git/87po42cwql.fsf@evledraar.gmail.com/) for more detailed numbers and a test script used to produce the numbers cited above.
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com> --- pack-objects.h | 28 +++++++++++++++++++++------- 1 file changed, 21 insertions(+), 7 deletions(-)
diff --git a/pack-objects.h b/pack-objects.h index 1c588184b2..e5456c6c89 100644 --- a/pack-objects.h +++ b/pack-objects.h @@ -28,6 +28,10 @@ enum dfs_state { }; /* + * 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 @@ -76,34 +80,44 @@ enum dfs_state { */ struct object_entry { struct pack_idx_entry idx; + void *delta_data; /* cached delta (uncompressed) */ + off_t in_pack_offset; + uint32_t hash; /* name hint hash */ unsigned size_:OE_SIZE_BITS; unsigned size_valid:1; - unsigned in_pack_idx:OE_IN_PACK_BITS; /* already in pack */ - off_t in_pack_offset; 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 */ - void *delta_data; /* cached delta (uncompressed) */ 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 type_valid:1; - uint32_t hash; /* name hint hash */ - unsigned char in_pack_header_size; 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; + + /* + * pahole results on 64-bit linux (gcc and clang) + * + * size: 80, bit_padding: 20 bits, holes: 8 bits + * + * and on 32-bit (gcc) + * + * size: 76, bit_padding: 20 bits, holes: 8 bits + */ }; struct packing_data {
-- 2.17.0.367.g5dd2e386c3