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git/pseudo-merge.c

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#define USE_THE_REPOSITORY_VARIABLE
#include "git-compat-util.h"
#include "pseudo-merge.h"
#include "date.h"
#include "oid-array.h"
#include "strbuf.h"
#include "config.h"
#include "string-list.h"
#include "refs.h"
#include "pack-bitmap.h"
#include "commit.h"
#include "alloc.h"
#include "progress.h"
#include "hex.h"
#define DEFAULT_PSEUDO_MERGE_DECAY 1.0
#define DEFAULT_PSEUDO_MERGE_MAX_MERGES 64
#define DEFAULT_PSEUDO_MERGE_SAMPLE_RATE 1
#define DEFAULT_PSEUDO_MERGE_THRESHOLD approxidate("1.week.ago")
#define DEFAULT_PSEUDO_MERGE_STABLE_THRESHOLD approxidate("1.month.ago")
#define DEFAULT_PSEUDO_MERGE_STABLE_SIZE 512
static double gitexp(double base, int exp)
{
double result = 1;
while (1) {
if (exp % 2)
result *= base;
exp >>= 1;
if (!exp)
break;
base *= base;
}
return result;
}
static uint32_t pseudo_merge_group_size(const struct pseudo_merge_group *group,
const struct pseudo_merge_matches *matches,
uint32_t i)
{
double C = 0.0f;
uint32_t n;
/*
* The size of pseudo-merge groups decays according to a power series,
* which looks like:
*
* f(n) = C * n^-k
*
* , where 'n' is the n-th pseudo-merge group, 'f(n)' is its size, 'k'
* is the decay rate, and 'C' is a scaling value.
*
* The value of C depends on the number of groups, decay rate, and total
* number of commits. It is computed such that if there are M and N
* total groups and commits, respectively, that:
*
* N = f(0) + f(1) + ... f(M-1)
*
* Rearranging to isolate C, we get:
*
* N = \sum_{n=1}^M C / n^k
*
* N / C = \sum_{n=1}^M n^-k
*
* C = N / \sum_{n=1}^M n^-k
*
* For example, if we have a decay rate of 'k' being equal to 1.5, 'N'
* total commits equal to 10,000, and 'M' being equal to 6 groups, then
* the (rounded) group sizes are:
*
* { 5469, 1934, 1053, 684, 489, 372 }
*
* increasing the number of total groups, say to 10, scales the group
* sizes appropriately:
*
* { 5012, 1772, 964, 626, 448, 341, 271, 221, 186, 158 }
*/
for (n = 0; n < group->max_merges; n++)
C += 1.0 / gitexp(n + 1, group->decay);
C = matches->unstable_nr / C;
return (uint32_t)((C / gitexp(i + 1, group->decay)) + 0.5);
}
static void pseudo_merge_group_init(struct pseudo_merge_group *group)
{
memset(group, 0, sizeof(struct pseudo_merge_group));
strmap_init_with_options(&group->matches, NULL, 0);
group->decay = DEFAULT_PSEUDO_MERGE_DECAY;
group->max_merges = DEFAULT_PSEUDO_MERGE_MAX_MERGES;
group->sample_rate = DEFAULT_PSEUDO_MERGE_SAMPLE_RATE;
group->threshold = DEFAULT_PSEUDO_MERGE_THRESHOLD;
group->stable_threshold = DEFAULT_PSEUDO_MERGE_STABLE_THRESHOLD;
group->stable_size = DEFAULT_PSEUDO_MERGE_STABLE_SIZE;
}
static int pseudo_merge_config(const char *var, const char *value,
const struct config_context *ctx,
void *cb_data)
{
struct string_list *list = cb_data;
struct string_list_item *item;
struct pseudo_merge_group *group;
struct strbuf buf = STRBUF_INIT;
const char *sub, *key;
size_t sub_len;
int ret = 0;
if (parse_config_key(var, "bitmappseudomerge", &sub, &sub_len, &key))
goto done;
if (!sub_len)
goto done;
strbuf_add(&buf, sub, sub_len);
item = string_list_lookup(list, buf.buf);
if (!item) {
item = string_list_insert(list, buf.buf);
item->util = xmalloc(sizeof(struct pseudo_merge_group));
pseudo_merge_group_init(item->util);
}
group = item->util;
if (!strcmp(key, "pattern")) {
struct strbuf re = STRBUF_INIT;
free(group->pattern);
if (*value != '^')
strbuf_addch(&re, '^');
strbuf_addstr(&re, value);
group->pattern = xcalloc(1, sizeof(regex_t));
if (regcomp(group->pattern, re.buf, REG_EXTENDED))
die(_("failed to load pseudo-merge regex for %s: '%s'"),
sub, re.buf);
strbuf_release(&re);
} else if (!strcmp(key, "decay")) {
group->decay = git_config_double(var, value, ctx->kvi);
if (group->decay < 0) {
warning(_("%s must be non-negative, using default"), var);
group->decay = DEFAULT_PSEUDO_MERGE_DECAY;
}
} else if (!strcmp(key, "samplerate")) {
group->sample_rate = git_config_double(var, value, ctx->kvi);
if (!(0 <= group->sample_rate && group->sample_rate <= 1)) {
warning(_("%s must be between 0 and 1, using default"), var);
group->sample_rate = DEFAULT_PSEUDO_MERGE_SAMPLE_RATE;
}
} else if (!strcmp(key, "threshold")) {
if (git_config_expiry_date(&group->threshold, var, value)) {
ret = -1;
goto done;
}
} else if (!strcmp(key, "maxmerges")) {
group->max_merges = git_config_int(var, value, ctx->kvi);
if (group->max_merges < 0) {
warning(_("%s must be non-negative, using default"), var);
group->max_merges = DEFAULT_PSEUDO_MERGE_MAX_MERGES;
}
} else if (!strcmp(key, "stablethreshold")) {
if (git_config_expiry_date(&group->stable_threshold, var, value)) {
ret = -1;
goto done;
}
} else if (!strcmp(key, "stablesize")) {
group->stable_size = git_config_int(var, value, ctx->kvi);
if (group->stable_size <= 0) {
warning(_("%s must be positive, using default"), var);
group->stable_size = DEFAULT_PSEUDO_MERGE_STABLE_SIZE;
}
}
done:
strbuf_release(&buf);
return ret;
}
void load_pseudo_merges_from_config(struct repository *r,
struct string_list *list)
{
struct string_list_item *item;
repo_config(r, pseudo_merge_config, list);
for_each_string_list_item(item, list) {
struct pseudo_merge_group *group = item->util;
if (!group->pattern)
die(_("pseudo-merge group '%s' missing required pattern"),
item->string);
if (group->threshold < group->stable_threshold)
die(_("pseudo-merge group '%s' has unstable threshold "
"before stable one"), item->string);
}
}
static int find_pseudo_merge_group_for_ref(const char *refname,
const char *referent UNUSED,
const struct object_id *oid,
int flags UNUSED,
void *_data)
{
struct bitmap_writer *writer = _data;
struct object_id peeled;
struct commit *c;
uint32_t i;
int has_bitmap;
if (!peel_iterated_oid(the_repository, oid, &peeled))
oid = &peeled;
c = lookup_commit(the_repository, oid);
if (!c)
return 0;
if (!packlist_find(writer->to_pack, oid))
return 0;
has_bitmap = bitmap_writer_has_bitmapped_object_id(writer, oid);
for (i = 0; i < writer->pseudo_merge_groups.nr; i++) {
struct pseudo_merge_group *group;
struct pseudo_merge_matches *matches;
struct strbuf group_name = STRBUF_INIT;
regmatch_t captures[16];
size_t j;
group = writer->pseudo_merge_groups.items[i].util;
if (regexec(group->pattern, refname, ARRAY_SIZE(captures),
captures, 0))
continue;
if (captures[ARRAY_SIZE(captures) - 1].rm_so != -1)
warning(_("pseudo-merge regex from config has too many capture "
"groups (max=%"PRIuMAX")"),
(uintmax_t)ARRAY_SIZE(captures) - 2);
for (j = !!group->pattern->re_nsub; j < ARRAY_SIZE(captures); j++) {
regmatch_t *match = &captures[j];
if (match->rm_so == -1)
continue;
if (group_name.len)
strbuf_addch(&group_name, '-');
strbuf_add(&group_name, refname + match->rm_so,
match->rm_eo - match->rm_so);
}
matches = strmap_get(&group->matches, group_name.buf);
if (!matches) {
matches = xcalloc(1, sizeof(*matches));
strmap_put(&group->matches, strbuf_detach(&group_name, NULL),
matches);
}
if (c->date <= group->stable_threshold) {
ALLOC_GROW(matches->stable, matches->stable_nr + 1,
matches->stable_alloc);
matches->stable[matches->stable_nr++] = c;
} else if (c->date <= group->threshold && !has_bitmap) {
ALLOC_GROW(matches->unstable, matches->unstable_nr + 1,
matches->unstable_alloc);
matches->unstable[matches->unstable_nr++] = c;
}
strbuf_release(&group_name);
}
return 0;
}
static struct commit *push_pseudo_merge(struct pseudo_merge_group *group)
{
struct commit *merge;
ALLOC_GROW(group->merges, group->merges_nr + 1, group->merges_alloc);
merge = alloc_commit_node(the_repository);
merge->object.parsed = 1;
merge->object.flags |= BITMAP_PSEUDO_MERGE;
group->merges[group->merges_nr++] = merge;
return merge;
}
static struct pseudo_merge_commit_idx *pseudo_merge_idx(kh_oid_map_t *pseudo_merge_commits,
const struct object_id *oid)
{
struct pseudo_merge_commit_idx *pmc;
int hash_ret;
khiter_t hash_pos = kh_put_oid_map(pseudo_merge_commits, *oid,
&hash_ret);
if (hash_ret) {
CALLOC_ARRAY(pmc, 1);
kh_value(pseudo_merge_commits, hash_pos) = pmc;
} else {
pmc = kh_value(pseudo_merge_commits, hash_pos);
}
return pmc;
}
#define MIN_PSEUDO_MERGE_SIZE 8
static void select_pseudo_merges_1(struct bitmap_writer *writer,
struct pseudo_merge_group *group,
struct pseudo_merge_matches *matches)
{
uint32_t i, j;
uint32_t stable_merges_nr;
if (!matches->stable_nr && !matches->unstable_nr)
return; /* all tips in this group already have bitmaps */
stable_merges_nr = matches->stable_nr / group->stable_size;
if (matches->stable_nr % group->stable_size)
stable_merges_nr++;
/* make stable_merges_nr pseudo merges for stable commits */
for (i = 0, j = 0; i < stable_merges_nr; i++) {
struct commit *merge;
struct commit_list **p;
merge = push_pseudo_merge(group);
p = &merge->parents;
/*
* For each pseudo-merge created above, add parents to the
* allocated commit node from the stable set of commits
* (un-bitmapped, newer than the stable threshold).
*/
do {
struct commit *c;
struct pseudo_merge_commit_idx *pmc;
if (j >= matches->stable_nr)
break;
c = matches->stable[j++];
/*
* Here and below, make sure that we keep our mapping of
* commits -> pseudo-merge(s) which include the key'd
* commit up-to-date.
*/
pmc = pseudo_merge_idx(writer->pseudo_merge_commits,
&c->object.oid);
ALLOC_GROW(pmc->pseudo_merge, pmc->nr + 1, pmc->alloc);
pmc->pseudo_merge[pmc->nr++] = writer->pseudo_merges_nr;
p = commit_list_append(c, p);
} while (j % group->stable_size);
if (merge->parents) {
bitmap_writer_push_commit(writer, merge, 1);
writer->pseudo_merges_nr++;
}
}
/* make up to group->max_merges pseudo merges for unstable commits */
for (i = 0, j = 0; i < group->max_merges; i++) {
struct commit *merge;
struct commit_list **p;
uint32_t size, end;
merge = push_pseudo_merge(group);
p = &merge->parents;
size = pseudo_merge_group_size(group, matches, i);
end = size < MIN_PSEUDO_MERGE_SIZE ? matches->unstable_nr : j + size;
/*
* For each pseudo-merge commit created above, add parents to
* the allocated commit node from the unstable set of commits
* (newer than the stable threshold).
*
* Account for the sample rate, since not every candidate from
* the set of stable commits will be included as a pseudo-merge
* parent.
*/
for (; j < end && j < matches->unstable_nr; j++) {
struct commit *c = matches->unstable[j];
struct pseudo_merge_commit_idx *pmc;
if (j % (uint32_t)(1.0 / group->sample_rate))
continue;
pmc = pseudo_merge_idx(writer->pseudo_merge_commits,
&c->object.oid);
ALLOC_GROW(pmc->pseudo_merge, pmc->nr + 1, pmc->alloc);
pmc->pseudo_merge[pmc->nr++] = writer->pseudo_merges_nr;
p = commit_list_append(c, p);
}
if (merge->parents) {
bitmap_writer_push_commit(writer, merge, 1);
writer->pseudo_merges_nr++; }
if (end >= matches->unstable_nr)
break;
}
}
static int commit_date_cmp(const void *va, const void *vb)
{
timestamp_t a = (*(const struct commit **)va)->date;
timestamp_t b = (*(const struct commit **)vb)->date;
if (a < b)
return -1;
else if (a > b)
return 1;
return 0;
}
static void sort_pseudo_merge_matches(struct pseudo_merge_matches *matches)
{
QSORT(matches->stable, matches->stable_nr, commit_date_cmp);
QSORT(matches->unstable, matches->unstable_nr, commit_date_cmp);
}
void select_pseudo_merges(struct bitmap_writer *writer)
{
struct progress *progress = NULL;
uint32_t i;
if (!writer->pseudo_merge_groups.nr)
return;
if (writer->show_progress)
progress = start_progress("Selecting pseudo-merge commits",
writer->pseudo_merge_groups.nr);
refs_for_each_ref(get_main_ref_store(the_repository),
find_pseudo_merge_group_for_ref, writer);
for (i = 0; i < writer->pseudo_merge_groups.nr; i++) {
struct pseudo_merge_group *group;
struct hashmap_iter iter;
struct strmap_entry *e;
group = writer->pseudo_merge_groups.items[i].util;
strmap_for_each_entry(&group->matches, &iter, e) {
struct pseudo_merge_matches *matches = e->value;
sort_pseudo_merge_matches(matches);
select_pseudo_merges_1(writer, group, matches);
}
display_progress(progress, i + 1);
}
stop_progress(&progress);
}
void free_pseudo_merge_map(struct pseudo_merge_map *pm)
{
uint32_t i;
for (i = 0; i < pm->nr; i++) {
ewah_pool_free(pm->v[i].commits);
ewah_pool_free(pm->v[i].bitmap);
}
free(pm->v);
}
struct pseudo_merge_commit_ext {
uint32_t nr;
const unsigned char *ptr;
};
static int pseudo_merge_ext_at(const struct pseudo_merge_map *pm,
struct pseudo_merge_commit_ext *ext, size_t at)
{
if (at >= pm->map_size)
return error(_("extended pseudo-merge read out-of-bounds "
"(%"PRIuMAX" >= %"PRIuMAX")"),
(uintmax_t)at, (uintmax_t)pm->map_size);
if (at + 4 >= pm->map_size)
return error(_("extended pseudo-merge entry is too short "
"(%"PRIuMAX" >= %"PRIuMAX")"),
(uintmax_t)(at + 4), (uintmax_t)pm->map_size);
ext->nr = get_be32(pm->map + at);
ext->ptr = pm->map + at + sizeof(uint32_t);
return 0;
}
struct ewah_bitmap *pseudo_merge_bitmap(const struct pseudo_merge_map *pm,
struct pseudo_merge *merge)
{
if (!merge->loaded_commits)
BUG("cannot use unloaded pseudo-merge bitmap");
if (!merge->loaded_bitmap) {
size_t at = merge->bitmap_at;
merge->bitmap = read_bitmap(pm->map, pm->map_size, &at);
merge->loaded_bitmap = 1;
}
return merge->bitmap;
}
struct pseudo_merge *use_pseudo_merge(const struct pseudo_merge_map *pm,
struct pseudo_merge *merge)
{
if (!merge->loaded_commits) {
size_t pos = merge->at;
merge->commits = read_bitmap(pm->map, pm->map_size, &pos);
merge->bitmap_at = pos;
merge->loaded_commits = 1;
}
return merge;
}
static struct pseudo_merge *pseudo_merge_at(const struct pseudo_merge_map *pm,
struct object_id *oid,
size_t want)
{
size_t lo = 0;
size_t hi = pm->nr;
while (lo < hi) {
size_t mi = lo + (hi - lo) / 2;
size_t got = pm->v[mi].at;
if (got == want)
return use_pseudo_merge(pm, &pm->v[mi]);
else if (got < want)
hi = mi;
else
lo = mi + 1;
}
warning(_("could not find pseudo-merge for commit %s at offset %"PRIuMAX),
oid_to_hex(oid), (uintmax_t)want);
return NULL;
}
struct pseudo_merge_commit {
uint32_t commit_pos;
uint64_t pseudo_merge_ofs;
};
#define PSEUDO_MERGE_COMMIT_RAWSZ (sizeof(uint32_t)+sizeof(uint64_t))
static void read_pseudo_merge_commit_at(struct pseudo_merge_commit *merge,
const unsigned char *at)
{
merge->commit_pos = get_be32(at);
merge->pseudo_merge_ofs = get_be64(at + sizeof(uint32_t));
}
static int nth_pseudo_merge_ext(const struct pseudo_merge_map *pm,
struct pseudo_merge_commit_ext *ext,
struct pseudo_merge_commit *merge,
uint32_t n)
{
size_t ofs;
if (n >= ext->nr)
return error(_("extended pseudo-merge lookup out-of-bounds "
"(%"PRIu32" >= %"PRIu32")"), n, ext->nr);
ofs = get_be64(ext->ptr + st_mult(n, sizeof(uint64_t)));
if (ofs >= pm->map_size)
return error(_("out-of-bounds read: (%"PRIuMAX" >= %"PRIuMAX")"),
(uintmax_t)ofs, (uintmax_t)pm->map_size);
read_pseudo_merge_commit_at(merge, pm->map + ofs);
return 0;
}
static unsigned apply_pseudo_merge(const struct pseudo_merge_map *pm,
struct pseudo_merge *merge,
struct bitmap *result,
struct bitmap *roots)
{
if (merge->satisfied)
return 0;
if (!ewah_bitmap_is_subset(merge->commits, roots ? roots : result))
return 0;
bitmap_or_ewah(result, pseudo_merge_bitmap(pm, merge));
if (roots)
bitmap_or_ewah(roots, pseudo_merge_bitmap(pm, merge));
merge->satisfied = 1;
return 1;
}
static int pseudo_merge_commit_cmp(const void *va, const void *vb)
{
struct pseudo_merge_commit merge;
uint32_t key = *(uint32_t*)va;
read_pseudo_merge_commit_at(&merge, vb);
if (key < merge.commit_pos)
return -1;
if (key > merge.commit_pos)
return 1;
return 0;
}
static struct pseudo_merge_commit *find_pseudo_merge(const struct pseudo_merge_map *pm,
uint32_t pos)
{
if (!pm->commits_nr)
return NULL;
return bsearch(&pos, pm->commits, pm->commits_nr,
PSEUDO_MERGE_COMMIT_RAWSZ, pseudo_merge_commit_cmp);
}
int apply_pseudo_merges_for_commit(const struct pseudo_merge_map *pm,
struct bitmap *result,
struct commit *commit, uint32_t commit_pos)
{
struct pseudo_merge *merge;
struct pseudo_merge_commit *merge_commit;
int ret = 0;
merge_commit = find_pseudo_merge(pm, commit_pos);
if (!merge_commit)
return 0;
if (merge_commit->pseudo_merge_ofs & ((uint64_t)1<<63)) {
struct pseudo_merge_commit_ext ext = { 0 };
off_t ofs = merge_commit->pseudo_merge_ofs & ~((uint64_t)1<<63);
uint32_t i;
if (pseudo_merge_ext_at(pm, &ext, ofs) < -1) {
warning(_("could not read extended pseudo-merge table "
"for commit %s"),
oid_to_hex(&commit->object.oid));
return ret;
}
for (i = 0; i < ext.nr; i++) {
if (nth_pseudo_merge_ext(pm, &ext, merge_commit, i) < 0)
return ret;
merge = pseudo_merge_at(pm, &commit->object.oid,
merge_commit->pseudo_merge_ofs);
if (!merge)
return ret;
if (apply_pseudo_merge(pm, merge, result, NULL))
ret++;
}
} else {
merge = pseudo_merge_at(pm, &commit->object.oid,
merge_commit->pseudo_merge_ofs);
if (!merge)
return ret;
if (apply_pseudo_merge(pm, merge, result, NULL))
ret++;
}
if (ret)
cascade_pseudo_merges(pm, result, NULL);
return ret;
}
int cascade_pseudo_merges(const struct pseudo_merge_map *pm,
struct bitmap *result,
struct bitmap *roots)
{
unsigned any_satisfied;
int ret = 0;
do {
struct pseudo_merge *merge;
uint32_t i;
any_satisfied = 0;
for (i = 0; i < pm->nr; i++) {
merge = use_pseudo_merge(pm, &pm->v[i]);
if (apply_pseudo_merge(pm, merge, result, roots)) {
any_satisfied |= 1;
ret++;
}
}
} while (any_satisfied);
return ret;
}
struct pseudo_merge *pseudo_merge_for_parents(const struct pseudo_merge_map *pm,
struct bitmap *parents)
{
struct pseudo_merge *match = NULL;
size_t i;
if (!pm->nr)
return NULL;
/*
* NOTE: this loop is quadratic in the worst-case (where no
* matching pseudo-merge bitmaps are found), but in practice
* this is OK for a few reasons:
*
* - Rejecting pseudo-merge bitmaps that do not match the
* given commit is done quickly (i.e. `bitmap_equals_ewah()`
* returns early when we know the two bitmaps aren't equal.
*
* - Already matched pseudo-merge bitmaps (which we track with
* the `->satisfied` bit here) are skipped as potential
* candidates.
*
* - The number of pseudo-merges should be small (in the
* hundreds for most repositories).
*
* If in the future this semi-quadratic behavior does become a
* problem, another approach would be to keep track of which
* pseudo-merges are still "viable" after enumerating the
* pseudo-merge commit's parents:
*
* - A pseudo-merge bitmap becomes non-viable when the bit(s)
* corresponding to one or more parent(s) of the given
* commit are not set in a candidate pseudo-merge's commits
* bitmap.
*
* - After processing all bits, enumerate the remaining set of
* viable pseudo-merge bitmaps, and check that their
* popcount() matches the number of parents in the given
* commit.
*/
for (i = 0; i < pm->nr; i++) {
struct pseudo_merge *candidate = use_pseudo_merge(pm, &pm->v[i]);
if (!candidate || candidate->satisfied)
continue;
if (!bitmap_equals_ewah(parents, candidate->commits))
continue;
match = candidate;
match->satisfied = 1;
break;
}
return match;
}
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