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index-pack: reduce object_entry size to save memory

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For each object in the input pack, we need one struct object_entry. On
x86-64, this struct is 64 bytes long. Although:

 - The 8 bytes for delta_depth and base_object_no are only useful when
   show_stat is set. And it's never set unless someone is debugging.

 - The three fields hdr_size, type and real_type take 4 bytes each
   even though they never use more than 4 bits.

By moving delta_depth and base_object_no out of struct object_entry
and make the other 3 fields one byte long instead of 4, we shrink 25%
of this struct.

On a 3.4M object repo (*) that's about 53MB. The saving is less
impressive compared to index-pack memory use for basic bookkeeping (**),
about 16%.

(*) linux-2.6.git already has 4M objects as of v3.19-rc7 so this is
not an unrealistic number of objects that we have to deal with.

(**)  3.4M * (sizeof(object_entry) + sizeof(delta_entry)) = 311MB

Brought-up-by: Matthew Sporleder <msporleder@gmail.com>
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Nguyễn Thái Ngọc Duy 2015-02-26 17:52:07 +07:00 committed by Junio C Hamano
parent 9874fca712
commit 417305764a
1 changed files with 19 additions and 11 deletions
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30
builtin/index-pack.c
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@ -18,9 +18,12 @@ static const char index_pack_usage[] =
struct object_entry {
struct pack_idx_entry idx;
unsigned long size;
unsigned int hdr_size;
enum object_type type;
enum object_type real_type;
unsigned char hdr_size;
signed char type;
signed char real_type;
};
struct object_stat {
unsigned delta_depth;
int base_object_no;
};
@ -64,6 +67,7 @@ struct delta_entry {
};
static struct object_entry *objects;
static struct object_stat *obj_stat;
static struct delta_entry *deltas;
static struct thread_local nothread_data;
static int nr_objects;
@ -873,13 +877,15 @@ static void resolve_delta(struct object_entry *delta_obj,
void *base_data, *delta_data;
if (show_stat) {
delta_obj->delta_depth = base->obj->delta_depth + 1;
int i = delta_obj - objects;
int j = base->obj - objects;
obj_stat[i].delta_depth = obj_stat[j].delta_depth + 1;
deepest_delta_lock();
if (deepest_delta < delta_obj->delta_depth)
deepest_delta = delta_obj->delta_depth;
if (deepest_delta < obj_stat[i].delta_depth)
deepest_delta = obj_stat[i].delta_depth;
deepest_delta_unlock();
obj_stat[i].base_object_no = j;
}
delta_obj->base_object_no = base->obj - objects;
delta_data = get_data_from_pack(delta_obj);
base_data = get_base_data(base);
result->obj = delta_obj;
@ -902,7 +908,7 @@ static void resolve_delta(struct object_entry *delta_obj,
* "want"; if so, swap in "set" and return true. Otherwise, leave it untouched
* and return false.
*/
static int compare_and_swap_type(enum object_type *type,
static int compare_and_swap_type(signed char *type,
enum object_type want,
enum object_type set)
{
@ -1499,7 +1505,7 @@ static void show_pack_info(int stat_only)
struct object_entry *obj = &objects[i];
if (is_delta_type(obj->type))
chain_histogram[obj->delta_depth - 1]++;
chain_histogram[obj_stat[i].delta_depth - 1]++;
if (stat_only)
continue;
printf("%s %-6s %lu %lu %"PRIuMAX,
@ -1508,8 +1514,8 @@ static void show_pack_info(int stat_only)
(unsigned long)(obj[1].idx.offset - obj->idx.offset),
(uintmax_t)obj->idx.offset);
if (is_delta_type(obj->type)) {
struct object_entry *bobj = &objects[obj->base_object_no];
printf(" %u %s", obj->delta_depth, sha1_to_hex(bobj->idx.sha1));
struct object_entry *bobj = &objects[obj_stat[i].base_object_no];
printf(" %u %s", obj_stat[i].delta_depth, sha1_to_hex(bobj->idx.sha1));
}
putchar('\n');
}
@ -1672,6 +1678,8 @@ int cmd_index_pack(int argc, const char **argv, const char *prefix)
curr_pack = open_pack_file(pack_name);
parse_pack_header();
objects = xcalloc(nr_objects + 1, sizeof(struct object_entry));
if (show_stat)
obj_stat = xcalloc(nr_objects + 1, sizeof(struct object_stat));
deltas = xcalloc(nr_objects, sizeof(struct delta_entry));
parse_pack_objects(pack_sha1);
resolve_deltas();