Once we know the number of objects in the input pack, we allocate an
array of nr_objects of struct delta_entry. On x86-64, this struct is
32 bytes long. The union delta_base, which is part of struct
delta_entry, provides enough space to store either ofs-delta (8 bytes)
or ref-delta (20 bytes).
Because ofs-delta encoding is more efficient space-wise and more
performant at runtime than ref-delta encoding, Git packers try to use
ofs-delta whenever possible, and it is expected that objects encoded
as ref-delta are minority.
In the best clone case where no ref-delta object is present, we waste
(20-8) * nr_objects bytes because of this union. That's about 38MB out
of 100MB for deltas[] with 3.4M objects, or 38%. deltas[] would be
around 62MB without the waste.
This patch attempts to eliminate that. deltas[] array is split into
two: one for ofs-delta and one for ref-delta. Many functions are also
duplicated because of this split. With this patch, ofs_deltas[] array
takes 51MB. ref_deltas[] should remain unallocated in clone case (0
bytes). This array grows as we see ref-delta. We save about half in
this case, or 25% of total bookkeeping.
The saving is more than the calculation above because some padding in
the old delta_entry struct is removed. ofs_delta_entry is 16 bytes,
including the 4 bytes padding. That's 13MB for padding, but packing
the struct could break platforms that do not support unaligned
access. If someone on 32-bit is really low on memory and only deals
with packs smaller than 2G, using 32-bit off_t would eliminate the
padding and save 27MB on top.
A note about ofs_deltas allocation. We could use ref_deltas memory
allocation strategy for ofs_deltas. But that probably just adds more
overhead on top. ofs-deltas are generally the majority (1/2 to 2/3) in
any pack. Incremental realloc may lead to too many memcpy. And if we
preallocate, say 1/2 or 2/3 of nr_objects initially, the growth rate
of ALLOC_GROW() could make this array larger than nr_objects, wasting
more memory.
Brought-up-by: Matthew Sporleder <msporleder@xxxxxxxxx>
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@xxxxxxxxx>
---
builtin/index-pack.c | 260 +++++++++++++++++++++++++++++++--------------------
1 file changed, 160 insertions(+), 100 deletions(-)
diff --git a/builtin/index-pack.c b/builtin/index-pack.c
index 9d854fb..3ed53e3 100644
--- a/builtin/index-pack.c
+++ b/builtin/index-pack.c
@@ -28,11 +28,6 @@ struct object_stat {
int base_object_no;
};
-union delta_base {
- unsigned char sha1[20];
- off_t offset;
-};
-
struct base_data {
struct base_data *base;
struct base_data *child;
@@ -52,26 +47,28 @@ struct thread_local {
int pack_fd;
};
-/*
- * Even if sizeof(union delta_base) == 24 on 64-bit archs, we really want
- * to memcmp() only the first 20 bytes.
- */
-#define UNION_BASE_SZ 20
-
#define FLAG_LINK (1u<<20)
#define FLAG_CHECKED (1u<<21)
-struct delta_entry {
- union delta_base base;
+struct ofs_delta_entry {
+ off_t offset;
+ int obj_no;
+};
+
+struct ref_delta_entry {
+ unsigned char sha1[20];
int obj_no;
};
static struct object_entry *objects;
static struct object_stat *obj_stat;
-static struct delta_entry *deltas;
+static struct ofs_delta_entry *ofs_deltas;
+static struct ref_delta_entry *ref_deltas;
static struct thread_local nothread_data;
static int nr_objects;
-static int nr_deltas;
+static int nr_ofs_deltas;
+static int nr_ref_deltas;
+static int ref_deltas_alloc;
static int nr_resolved_deltas;
static int nr_threads;
@@ -480,7 +477,8 @@ static void *unpack_entry_data(unsigned long offset, unsigned long size,
}
static void *unpack_raw_entry(struct object_entry *obj,
- union delta_base *delta_base,
+ off_t *ofs_offset,
+ unsigned char *ref_sha1,
unsigned char *sha1)
{
unsigned char *p;
@@ -509,11 +507,10 @@ static void *unpack_raw_entry(struct object_entry *obj,
switch (obj->type) {
case OBJ_REF_DELTA:
- hashcpy(delta_base->sha1, fill(20));
+ hashcpy(ref_sha1, fill(20));
use(20);
break;
case OBJ_OFS_DELTA:
- memset(delta_base, 0, sizeof(*delta_base));
p = fill(1);
c = *p;
use(1);
@@ -527,8 +524,8 @@ static void *unpack_raw_entry(struct object_entry *obj,
use(1);
base_offset = (base_offset << 7) + (c & 127);
}
- delta_base->offset = obj->idx.offset - base_offset;
- if (delta_base->offset <= 0 || delta_base->offset >= obj->idx.offset)
+ *ofs_offset = obj->idx.offset - base_offset;
+ if (*ofs_offset <= 0 || *ofs_offset >= obj->idx.offset)
bad_object(obj->idx.offset, _("delta base offset is out of bound"));
break;
case OBJ_COMMIT:
@@ -612,55 +609,108 @@ static void *get_data_from_pack(struct object_entry *obj)
return unpack_data(obj, NULL, NULL);
}
-static int compare_delta_bases(const union delta_base *base1,
- const union delta_base *base2,
- enum object_type type1,
- enum object_type type2)
+static int compare_ofs_delta_bases(off_t offset1, off_t offset2,
+ enum object_type type1,
+ enum object_type type2)
{
int cmp = type1 - type2;
if (cmp)
return cmp;
- return memcmp(base1, base2, UNION_BASE_SZ);
+ return offset1 - offset2;
}
-static int find_delta(const union delta_base *base, enum object_type type)
+static int find_ofs_delta(const off_t offset, enum object_type type)
{
- int first = 0, last = nr_deltas;
-
- while (first < last) {
- int next = (first + last) / 2;
- struct delta_entry *delta = &deltas[next];
- int cmp;
-
- cmp = compare_delta_bases(base, &delta->base,
- type, objects[delta->obj_no].type);
- if (!cmp)
- return next;
- if (cmp < 0) {
- last = next;
- continue;
- }
- first = next+1;
- }
- return -first-1;
+ int first = 0, last = nr_ofs_deltas;
+
+ while (first < last) {
+ int next = (first + last) / 2;
+ struct ofs_delta_entry *delta = &ofs_deltas[next];
+ int cmp;
+
+ cmp = compare_ofs_delta_bases(offset, delta->offset,
+ type, objects[delta->obj_no].type);
+ if (!cmp)
+ return next;
+ if (cmp < 0) {
+ last = next;
+ continue;
+ }
+ first = next+1;
+ }
+ return -first-1;
}
-static void find_delta_children(const union delta_base *base,
- int *first_index, int *last_index,
- enum object_type type)
+static void find_ofs_delta_children(off_t offset,
+ int *first_index, int *last_index,
+ enum object_type type)
{
- int first = find_delta(base, type);
+ int first = find_ofs_delta(offset, type);
int last = first;
- int end = nr_deltas - 1;
+ int end = nr_ofs_deltas - 1;
if (first < 0) {
*first_index = 0;
*last_index = -1;
return;
}
- while (first > 0 && !memcmp(&deltas[first - 1].base, base, UNION_BASE_SZ))
+ while (first > 0 && ofs_deltas[first - 1].offset == offset)
--first;
- while (last < end && !memcmp(&deltas[last + 1].base, base, UNION_BASE_SZ))
+ while (last < end && ofs_deltas[last + 1].offset == offset)
+ ++last;
+ *first_index = first;
+ *last_index = last;
+}
+
+static int compare_ref_delta_bases(const unsigned char *sha1,
+ const unsigned char *sha2,
+ enum object_type type1,
+ enum object_type type2)
+{
+ int cmp = type1 - type2;
+ if (cmp)
+ return cmp;
+ return hashcmp(sha1, sha2);
+}
+
+static int find_ref_delta(const unsigned char *sha1, enum object_type type)
+{
+ int first = 0, last = nr_ref_deltas;
+
+ while (first < last) {
+ int next = (first + last) / 2;
+ struct ref_delta_entry *delta = &ref_deltas[next];
+ int cmp;
+
+ cmp = compare_ref_delta_bases(sha1, delta->sha1,
+ type, objects[delta->obj_no].type);
+ if (!cmp)
+ return next;
+ if (cmp < 0) {
+ last = next;
+ continue;
+ }
+ first = next+1;
+ }
+ return -first-1;
+}
+
+static void find_ref_delta_children(const unsigned char *sha1,
+ int *first_index, int *last_index,
+ enum object_type type)
+{
+ int first = find_ref_delta(sha1, type);
+ int last = first;
+ int end = nr_ref_deltas - 1;
+
+ if (first < 0) {
+ *first_index = 0;
+ *last_index = -1;
+ return;
+ }
+ while (first > 0 && !hashcmp(ref_deltas[first - 1].sha1, sha1))
+ --first;
+ while (last < end && !hashcmp(ref_deltas[last + 1].sha1, sha1))
++last;
*first_index = first;
*last_index = last;
@@ -927,16 +977,13 @@ static struct base_data *find_unresolved_deltas_1(struct base_data *base,
struct base_data *prev_base)
{
if (base->ref_last == -1 && base->ofs_last == -1) {
- union delta_base base_spec;
-
- hashcpy(base_spec.sha1, base->obj->idx.sha1);
- find_delta_children(&base_spec,
- &base->ref_first, &base->ref_last, OBJ_REF_DELTA);
+ find_ref_delta_children(base->obj->idx.sha1,
+ &base->ref_first, &base->ref_last,
+ OBJ_REF_DELTA);
- memset(&base_spec, 0, sizeof(base_spec));
- base_spec.offset = base->obj->idx.offset;
- find_delta_children(&base_spec,
- &base->ofs_first, &base->ofs_last, OBJ_OFS_DELTA);
+ find_ofs_delta_children(base->obj->idx.offset,
+ &base->ofs_first, &base->ofs_last,
+ OBJ_OFS_DELTA);
if (base->ref_last == -1 && base->ofs_last == -1) {
free(base->data);
@@ -947,7 +994,7 @@ static struct base_data *find_unresolved_deltas_1(struct base_data *base,
}
if (base->ref_first <= base->ref_last) {
- struct object_entry *child = objects + deltas[base->ref_first].obj_no;
+ struct object_entry *child = objects + ref_deltas[base->ref_first].obj_no;
struct base_data *result = alloc_base_data();
if (!compare_and_swap_type(&child->real_type, OBJ_REF_DELTA,
@@ -963,7 +1010,7 @@ static struct base_data *find_unresolved_deltas_1(struct base_data *base,
}
if (base->ofs_first <= base->ofs_last) {
- struct object_entry *child = objects + deltas[base->ofs_first].obj_no;
+ struct object_entry *child = objects + ofs_deltas[base->ofs_first].obj_no;
struct base_data *result = alloc_base_data();
assert(child->real_type == OBJ_OFS_DELTA);
@@ -999,15 +1046,20 @@ static void find_unresolved_deltas(struct base_data *base)
}
}
-static int compare_delta_entry(const void *a, const void *b)
+static int compare_ofs_delta_entry(const void *a, const void *b)
+{
+ const struct ofs_delta_entry *delta_a = a;
+ const struct ofs_delta_entry *delta_b = b;
+
+ return delta_a->offset - delta_b->offset;
+}
+
+static int compare_ref_delta_entry(const void *a, const void *b)
{
- const struct delta_entry *delta_a = a;
- const struct delta_entry *delta_b = b;
+ const struct ref_delta_entry *delta_a = a;
+ const struct ref_delta_entry *delta_b = b;
- /* group by type (ref vs ofs) and then by value (sha-1 or offset) */
- return compare_delta_bases(&delta_a->base, &delta_b->base,
- objects[delta_a->obj_no].type,
- objects[delta_b->obj_no].type);
+ return hashcmp(delta_a->sha1, delta_b->sha1);
}
static void resolve_base(struct object_entry *obj)
@@ -1053,7 +1105,8 @@ static void *threaded_second_pass(void *data)
static void parse_pack_objects(unsigned char *sha1)
{
int i, nr_delays = 0;
- struct delta_entry *delta = deltas;
+ struct ofs_delta_entry *ofs_delta = ofs_deltas;
+ unsigned char ref_delta_sha1[20];
struct stat st;
if (verbose)
@@ -1062,12 +1115,18 @@ static void parse_pack_objects(unsigned char *sha1)
nr_objects);
for (i = 0; i < nr_objects; i++) {
struct object_entry *obj = &objects[i];
- void *data = unpack_raw_entry(obj, &delta->base, obj->idx.sha1);
+ void *data = unpack_raw_entry(obj, &ofs_delta->offset,
+ ref_delta_sha1, obj->idx.sha1);
obj->real_type = obj->type;
- if (is_delta_type(obj->type)) {
- nr_deltas++;
- delta->obj_no = i;
- delta++;
+ if (obj->type == OBJ_OFS_DELTA) {
+ nr_ofs_deltas++;
+ ofs_delta->obj_no = i;
+ ofs_delta++;
+ } else if (obj->type == OBJ_REF_DELTA) {
+ ALLOC_GROW(ref_deltas, nr_ref_deltas + 1, ref_deltas_alloc);
+ hashcpy(ref_deltas[nr_ref_deltas].sha1, ref_delta_sha1);
+ ref_deltas[nr_ref_deltas].obj_no = i;
+ nr_ref_deltas++;
} else if (!data) {
/* large blobs, check later */
obj->real_type = OBJ_BAD;
@@ -1118,15 +1177,18 @@ static void resolve_deltas(void)
{
int i;
- if (!nr_deltas)
+ if (!nr_ofs_deltas && !nr_ref_deltas)
return;
/* Sort deltas by base SHA1/offset for fast searching */
- qsort(deltas, nr_deltas, sizeof(struct delta_entry),
- compare_delta_entry);
+ qsort(ofs_deltas, nr_ofs_deltas, sizeof(struct ofs_delta_entry),
+ compare_ofs_delta_entry);
+ qsort(ref_deltas, nr_ref_deltas, sizeof(struct ref_delta_entry),
+ compare_ref_delta_entry);
if (verbose)
- progress = start_progress(_("Resolving deltas"), nr_deltas);
+ progress = start_progress(_("Resolving deltas"),
+ nr_ref_deltas + nr_ofs_deltas);
#ifndef NO_PTHREADS
nr_dispatched = 0;
@@ -1164,7 +1226,7 @@ static void resolve_deltas(void)
static void fix_unresolved_deltas(struct sha1file *f, int nr_unresolved);
static void conclude_pack(int fix_thin_pack, const char *curr_pack, unsigned char *pack_sha1)
{
- if (nr_deltas == nr_resolved_deltas) {
+ if (nr_ref_deltas + nr_ofs_deltas == nr_resolved_deltas) {
stop_progress(&progress);
/* Flush remaining pack final 20-byte SHA1. */
flush();
@@ -1175,7 +1237,7 @@ static void conclude_pack(int fix_thin_pack, const char *curr_pack, unsigned cha
struct sha1file *f;
unsigned char read_sha1[20], tail_sha1[20];
struct strbuf msg = STRBUF_INIT;
- int nr_unresolved = nr_deltas - nr_resolved_deltas;
+ int nr_unresolved = nr_ofs_deltas + nr_ref_deltas - nr_resolved_deltas;
int nr_objects_initial = nr_objects;
if (nr_unresolved <= 0)
die(_("confusion beyond insanity"));
@@ -1197,11 +1259,11 @@ static void conclude_pack(int fix_thin_pack, const char *curr_pack, unsigned cha
die(_("Unexpected tail checksum for %s "
"(disk corruption?)"), curr_pack);
}
- if (nr_deltas != nr_resolved_deltas)
+ if (nr_ofs_deltas + nr_ref_deltas != nr_resolved_deltas)
die(Q_("pack has %d unresolved delta",
"pack has %d unresolved deltas",
- nr_deltas - nr_resolved_deltas),
- nr_deltas - nr_resolved_deltas);
+ nr_ofs_deltas + nr_ref_deltas - nr_resolved_deltas),
+ nr_ofs_deltas + nr_ref_deltas - nr_resolved_deltas);
}
static int write_compressed(struct sha1file *f, void *in, unsigned int size)
@@ -1261,14 +1323,14 @@ static struct object_entry *append_obj_to_pack(struct sha1file *f,
static int delta_pos_compare(const void *_a, const void *_b)
{
- struct delta_entry *a = *(struct delta_entry **)_a;
- struct delta_entry *b = *(struct delta_entry **)_b;
+ struct ref_delta_entry *a = *(struct ref_delta_entry **)_a;
+ struct ref_delta_entry *b = *(struct ref_delta_entry **)_b;
return a->obj_no - b->obj_no;
}
static void fix_unresolved_deltas(struct sha1file *f, int nr_unresolved)
{
- struct delta_entry **sorted_by_pos;
+ struct ref_delta_entry **sorted_by_pos;
int i, n = 0;
/*
@@ -1282,28 +1344,25 @@ static void fix_unresolved_deltas(struct sha1file *f, int nr_unresolved)
* resolving deltas in the same order as their position in the pack.
*/
sorted_by_pos = xmalloc(nr_unresolved * sizeof(*sorted_by_pos));
- for (i = 0; i < nr_deltas; i++) {
- if (objects[deltas[i].obj_no].real_type != OBJ_REF_DELTA)
- continue;
- sorted_by_pos[n++] = &deltas[i];
- }
+ for (i = 0; i < nr_ref_deltas; i++)
+ sorted_by_pos[n++] = &ref_deltas[i];
qsort(sorted_by_pos, n, sizeof(*sorted_by_pos), delta_pos_compare);
for (i = 0; i < n; i++) {
- struct delta_entry *d = sorted_by_pos[i];
+ struct ref_delta_entry *d = sorted_by_pos[i];
enum object_type type;
struct base_data *base_obj = alloc_base_data();
if (objects[d->obj_no].real_type != OBJ_REF_DELTA)
continue;
- base_obj->data = read_sha1_file(d->base.sha1, &type, &base_obj->size);
+ base_obj->data = read_sha1_file(d->sha1, &type, &base_obj->size);
if (!base_obj->data)
continue;
- if (check_sha1_signature(d->base.sha1, base_obj->data,
+ if (check_sha1_signature(d->sha1, base_obj->data,
base_obj->size, typename(type)))
- die(_("local object %s is corrupt"), sha1_to_hex(d->base.sha1));
- base_obj->obj = append_obj_to_pack(f, d->base.sha1,
+ die(_("local object %s is corrupt"), sha1_to_hex(d->sha1));
+ base_obj->obj = append_obj_to_pack(f, d->sha1,
base_obj->data, base_obj->size, type);
find_unresolved_deltas(base_obj);
display_progress(progress, nr_resolved_deltas);
@@ -1495,7 +1554,7 @@ static void read_idx_option(struct pack_idx_option *opts, const char *pack_name)
static void show_pack_info(int stat_only)
{
- int i, baseobjects = nr_objects - nr_deltas;
+ int i, baseobjects = nr_objects - nr_ref_deltas - nr_ofs_deltas;
unsigned long *chain_histogram = NULL;
if (deepest_delta)
@@ -1680,11 +1739,12 @@ int cmd_index_pack(int argc, const char **argv, const char *prefix)
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));
+ ofs_deltas = xcalloc(nr_objects, sizeof(struct ofs_delta_entry));
parse_pack_objects(pack_sha1);
resolve_deltas();
conclude_pack(fix_thin_pack, curr_pack, pack_sha1);
- free(deltas);
+ free(ofs_deltas);
+ free(ref_deltas);
if (strict)
foreign_nr = check_objects();
--
2.3.0.rc1.137.g477eb31
--
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