/src/git/pseudo-merge.c

Source (jump to first uncovered line)
#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;
}

Coverage Report

Created: 2024-09-08 06:23