On Sat, Mar 17 2018, Nguyễn Thái Ngọc Duy jotted:
> 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, 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).
Given what I mentioned in 87po42cwql.fsf@xxxxxxxxxxxxxxxxxxx just now I
think we should add this to the commit message.
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.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.git) has shown a
7.9% reduction, so the overall expected improvement should be
somewhere around 8%.
See 87po42cwql.fsf@xxxxxxxxxxxxxxxxxxx on-list
(https://public-inbox.org/git/87po42cwql.fsf@xxxxxxxxxxxxxxxxxxx/)
for more detailed numbers and a test script used to produce the
numbers cited above.
Thanks again for working on this.
> Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@xxxxxxxxx>
> ---
> pack-objects.h | 17 +++++++++--------
> 1 file changed, 9 insertions(+), 8 deletions(-)
>
> diff --git a/pack-objects.h b/pack-objects.h
> index 2507b157d5..8979289f5f 100644
> --- a/pack-objects.h
> +++ b/pack-objects.h
> @@ -71,35 +71,36 @@ enum dfs_state {
> */
> struct object_entry {
> struct pack_idx_entry idx;
> - /* object uncompressed size _if_ size_valid is true */
> - uint32_t size_;
> - unsigned size_valid:1;
> - unsigned in_pack_idx:OE_IN_PACK_BITS; /* already in pack */
> + void *delta_data; /* cached delta (uncompressed) */
> off_t in_pack_offset;
> + uint32_t hash; /* name hint hash */
> + uint32_t size_; /* object uncompressed size _if_ size_valid is true */
> 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) */
> uint32_t delta_size_:OE_DELTA_SIZE_BITS; /* delta data size (uncompressed) */
> uint32_t delta_size_valid:1;
> + unsigned in_pack_idx:OE_IN_PACK_BITS; /* already in pack */
> + unsigned size_valid:1;
> unsigned z_delta_size:OE_Z_DELTA_BITS;
> + unsigned type_valid:1;
> unsigned type_:TYPE_BITS;
> 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 char in_pack_header_size;
> unsigned tagged:1; /* near the very tip of refs */
> unsigned filled:1; /* assigned write-order */
> unsigned dfs_state:OE_DFS_STATE_BITS;
> unsigned depth:OE_DEPTH_BITS;
> +
> + /* size: 80, bit_padding: 16 bits */
> };
>
> struct packing_data {
