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pack-objects: shrink z_delta_size field in struct object_entry 

We only cache deltas when it's smaller than a certain limit. This limit
defaults to 1000 but save its compressed length in a 64-bit field.
Shrink that field down to 20 bits, so you can only cache 1MB deltas.
Larger deltas must be recomputed at when the pack is written down.

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 2018-04-14 17:35:07 +02:00 committed by Junio C Hamano
parent 898eba5e63
commit 0cb3c1427a
3 changed files with 22 additions and 8 deletions
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3
Documentation/config.txt
View File

@ -2459,7 +2459,8 @@ 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

24
builtin/pack-objects.c
View File

@ -2099,12 +2099,19 @@ static void find_deltas(struct object_entry **list, unsigned *list_size,
* between writes at that moment.
*/
if (entry->delta_data && !pack_to_stdout) {
entry->z_delta_size = do_compress(&entry->delta_data,
entry->delta_size);
cache_lock();
delta_cache_size -= entry->delta_size;
delta_cache_size += entry->z_delta_size;
cache_unlock();
unsigned long size;
size = do_compress(&entry->delta_data, entry->delta_size);
if (size < (1U << OE_Z_DELTA_BITS)) {
entry->z_delta_size = size;
cache_lock();
delta_cache_size -= entry->delta_size;
delta_cache_size += entry->z_delta_size;
cache_unlock();
} else {
FREE_AND_NULL(entry->delta_data);
entry->z_delta_size = 0;
}
}
/* if we made n a delta, and if n is already at max
@ -3087,6 +3094,11 @@ int cmd_pack_objects(int argc, const char **argv, const char *prefix)
depth, (1 << OE_DEPTH_BITS) - 1);
depth = (1 << OE_DEPTH_BITS) - 1;
}
if (cache_max_small_delta_size >= (1U << OE_Z_DELTA_BITS)) {
warning(_("pack.deltaCacheLimit is too high, forcing %d"),
(1U << OE_Z_DELTA_BITS) - 1);
cache_max_small_delta_size = (1U << OE_Z_DELTA_BITS) - 1;
}
argv_array_push(&rp, "pack-objects");
if (thin) {

3
pack-objects.h
View File

@ -6,6 +6,7 @@
#define OE_DFS_STATE_BITS 2
#define OE_DEPTH_BITS 12
#define OE_IN_PACK_BITS 10
#define OE_Z_DELTA_BITS 20
/*
* State flags for depth-first search used for analyzing delta cycles.
@ -77,7 +78,7 @@ struct object_entry {
*/
void *delta_data; /* cached delta (uncompressed) */
unsigned long delta_size; /* delta data size (uncompressed) */
unsigned long z_delta_size; /* delta data size (compressed) */
unsigned z_delta_size:OE_Z_DELTA_BITS;
unsigned type_:TYPE_BITS;
unsigned in_pack_type:TYPE_BITS; /* could be delta */
unsigned type_valid:1;