gc_stats.c

/**************************************************************************/
/*                                                                        */
/*                                 OCaml                                  */
/*                                                                        */
/*             Gabriel Scherer, projet Partout, INRIA Saclay              */
/*                                                                        */
/*   Copyright 2022 Institut National de Recherche en Informatique et     */
/*     en Automatique.                                                    */
/*                                                                        */
/*   All rights reserved.  This file is distributed under the terms of    */
/*   the GNU Lesser General Public License version 2.1, with the          */
/*   special exception on linking described in the file LICENSE.          */
/*                                                                        */
/**************************************************************************/

#define CAML_INTERNALS

#include "caml/gc_stats.h"
#include "caml/minor_gc.h"
#include "caml/shared_heap.h"

Caml_inline intnat intnat_max(intnat a, intnat b) {
  return (a > b ? a : b);
}

void caml_accum_heap_stats(struct heap_stats* acc, const struct heap_stats* h)
{
  acc->pool_words += h->pool_words;
  acc->pool_max_words = intnat_max(acc->pool_max_words, acc->pool_words);
  acc->pool_max_words = intnat_max(acc->pool_max_words, h->pool_max_words);
  acc->pool_live_words += h->pool_live_words;
  acc->pool_live_blocks += h->pool_live_blocks;
  acc->pool_frag_words += h->pool_frag_words;
  acc->large_words += h->large_words;
  acc->large_max_words = intnat_max(acc->large_max_words, acc->large_words);
  acc->large_max_words = intnat_max(acc->large_max_words, h->large_max_words);
  acc->large_blocks += h->large_blocks;
}

void caml_remove_heap_stats(struct heap_stats* acc, const struct heap_stats* h)
{
  acc->pool_words -= h->pool_words;
  acc->pool_live_words -= h->pool_live_words;
  acc->pool_live_blocks -= h->pool_live_blocks;
  acc->pool_frag_words -= h->pool_frag_words;
  acc->large_words -= h->large_words;
  acc->large_blocks -= h->large_blocks;
}

void caml_accum_alloc_stats(
  struct alloc_stats* acc,
  const struct alloc_stats* s)
{
  acc->minor_words += s->minor_words;
  acc->promoted_words += s->promoted_words;
  acc->major_words += s->major_words;
  acc->forced_major_collections += s->forced_major_collections;
}

void caml_collect_alloc_stats_sample(
  caml_domain_state *local,
  struct alloc_stats *sample)
{
  sample->minor_words = local->stat_minor_words;
  sample->promoted_words = local->stat_promoted_words;
  sample->major_words = local->stat_major_words;
  sample->forced_major_collections = local->stat_forced_major_collections;
}

void caml_reset_domain_alloc_stats(caml_domain_state *local)
{
  local->stat_minor_words = 0;
  local->stat_promoted_words = 0;
  local->stat_major_words = 0;
  local->stat_forced_major_collections = 0;
}


/* We handle orphaning allocation stats here,
   whereas orphaning of heap stats is done in shared_heap.c */
static caml_plat_mutex orphan_lock = CAML_PLAT_MUTEX_INITIALIZER;
static struct alloc_stats orphaned_alloc_stats = {0,};

void caml_accum_orphan_alloc_stats(struct alloc_stats *acc) {
  caml_plat_lock(&orphan_lock);
  caml_accum_alloc_stats(acc, &orphaned_alloc_stats);
  caml_plat_unlock(&orphan_lock);
}

void caml_orphan_alloc_stats(caml_domain_state *domain) {
  struct alloc_stats alloc_stats;

  /* move alloc stats from the domain to [alloc_stats] */
  caml_collect_alloc_stats_sample(domain, &alloc_stats);
  caml_reset_domain_alloc_stats(domain);

  /* push them into the orphan stats */
  caml_plat_lock(&orphan_lock);
  caml_accum_alloc_stats(&orphaned_alloc_stats, &alloc_stats);
  caml_plat_unlock(&orphan_lock);
}


/* The "sampled stats" of a domain are a recent copy of its
   domain-local stats, accessed without synchronization and only
   updated ("sampled") during stop-the-world events -- each minor
   collection, and on domain termination. */
static struct gc_stats sampled_gc_stats[Max_domains];

/* Update the sampled stats for the given domain. */
void caml_collect_gc_stats_sample(caml_domain_state* domain)
{
  struct gc_stats* stats = &sampled_gc_stats[domain->id];
  caml_collect_alloc_stats_sample(domain, &stats->alloc_stats);
  caml_collect_heap_stats_sample(domain->shared_heap, &stats->heap_stats);
}

void caml_clear_gc_stats_sample(caml_domain_state *domain) {
  struct gc_stats* stats = &sampled_gc_stats[domain->id];
  memset(stats, 0, sizeof(*stats));
}

/* Compute global stats for the whole runtime. */
void caml_compute_gc_stats(struct gc_stats* buf)
{
  int i;
  intnat pool_max = 0, large_max = 0;
  int my_id = Caml_state->id;
  memset(buf, 0, sizeof(*buf));

  caml_accum_orphan_heap_stats(&buf->heap_stats);
  caml_accum_orphan_alloc_stats(&buf->alloc_stats);

  /* The instantaneous maximum heap size cannot be computed
     from per-domain statistics, and would be very expensive
     to maintain directly. Here, we just sum the per-domain
     maxima, which is completely wrong.

     FIXME: maybe maintain coarse global maxima?

     The summation starts here from the orphan-heap maxima.
  */
  pool_max = buf->heap_stats.pool_max_words;
  large_max = buf->heap_stats.large_max_words;

  for (i=0; i<Max_domains; i++) {
    /* For allocation stats, we use the live stats of the current domain
       and the sampled stats of other domains.

       For the heap stats, we always used the sampled stats. */
    struct gc_stats* s = &sampled_gc_stats[i];
    if (i != my_id) {
      caml_accum_alloc_stats(&buf->alloc_stats, &s->alloc_stats);
      caml_accum_heap_stats(&buf->heap_stats, &s->heap_stats);
    }
    else {
      struct alloc_stats alloc_stats;
      caml_collect_alloc_stats_sample(Caml_state, &alloc_stats);
      caml_accum_alloc_stats(&buf->alloc_stats, &alloc_stats);
      caml_accum_heap_stats(&buf->heap_stats, &s->heap_stats);
      //FIXME use live heap stats instead of sampled heap stats below?
    }
    pool_max += s->heap_stats.pool_max_words;
    large_max += s->heap_stats.large_max_words;
  }
  buf->heap_stats.pool_max_words = pool_max;
  buf->heap_stats.large_max_words = large_max;
}