(re-factor) gc: Remove redundant since_sweep field (#49195)

This field is at all times 0 or identical to allocd, so this change
removes it in preference of `gc_num.allocd`. Hopefully this makes the
GC metrics a bit easier to interpret for newcomers.

base/timing.jl

@@ -12,7 +12,6 @@ struct GC_Num
  freecall ::Int64
  total_time ::Int64
  total_allocd ::Int64 # GC internal
- since_sweep ::Int64 # GC internal
  collect ::Csize_t # GC internal
  pause ::Cint
  full_sweep ::Cint

src/gc.c

@@ -3184,22 +3184,21 @@ static int _jl_gc_collect(jl_ptls_t ptls, jl_gc_collection_t collection)
  mark_reset_age = 0;
  }
 
- gc_num.since_sweep += gc_num.allocd;
  JL_PROBE_GC_MARK_END(scanned_bytes, perm_scanned_bytes);
  gc_settime_premark_end();
  gc_time_mark_pause(gc_start_time, scanned_bytes, perm_scanned_bytes);
  uint64_t end_mark_time = jl_hrtime();
  uint64_t mark_time = end_mark_time - start_mark_time;
  gc_num.mark_time = mark_time;
  gc_num.total_mark_time += mark_time;
- int64_t actual_allocd = gc_num.since_sweep;
+ int64_t allocd = gc_num.allocd;
  gc_settime_postmark_end();
  // marking is over
 
  // Flush everything in mark cache
  gc_sync_all_caches_nolock(ptls);
 
- int64_t live_sz_ub = live_bytes + actual_allocd;
+ int64_t live_sz_ub = live_bytes + allocd;
  int64_t live_sz_est = scanned_bytes + perm_scanned_bytes;
  int64_t estimate_freed = live_sz_ub - live_sz_est;
 
@@ -3209,11 +3208,11 @@ static int _jl_gc_collect(jl_ptls_t ptls, jl_gc_collection_t collection)
  gc_stats_big_obj();
  objprofile_printall();
  objprofile_reset();
- gc_num.total_allocd += gc_num.since_sweep;
+ gc_num.total_allocd += gc_num.allocd;
  if (!prev_sweep_full)
  promoted_bytes += perm_scanned_bytes - last_perm_scanned_bytes;
  // 5. next collection decision
- int not_freed_enough = (collection == JL_GC_AUTO) && estimate_freed < (7*(actual_allocd/10));
+ int not_freed_enough = (collection == JL_GC_AUTO) && estimate_freed < (7*(allocd/10));
  int nptr = 0;
  assert(gc_n_threads);
  for (int i = 0; i < gc_n_threads; i++) {
@@ -3334,17 +3333,16 @@ static int _jl_gc_collect(jl_ptls_t ptls, jl_gc_collection_t collection)
  _report_gc_finished(pause, gc_num.freed, sweep_full, recollect);
 
  gc_final_pause_end(gc_start_time, gc_end_time);
- gc_time_sweep_pause(gc_end_time, actual_allocd, live_bytes,
+ gc_time_sweep_pause(gc_end_time, allocd, live_bytes,
  estimate_freed, sweep_full);
  gc_num.full_sweep += sweep_full;
  uint64_t max_memory = last_live_bytes + gc_num.allocd;
  if (max_memory > gc_num.max_memory) {
  gc_num.max_memory = max_memory;
  }
 
- gc_num.allocd = 0;
  last_live_bytes = live_bytes;
- live_bytes += -gc_num.freed + gc_num.since_sweep;
+ live_bytes += -gc_num.freed + gc_num.allocd;
 
  if (collection == JL_GC_AUTO) {
  //If we aren't freeing enough or are seeing lots and lots of pointers let it increase faster
@@ -3386,7 +3384,7 @@ static int _jl_gc_collect(jl_ptls_t ptls, jl_gc_collection_t collection)
  prev_sweep_full = sweep_full;
  gc_num.pause += !recollect;
  gc_num.total_time += pause;
- gc_num.since_sweep = 0;
+ gc_num.allocd = 0;
  gc_num.freed = 0;
  if (pause > gc_num.max_pause) {
  gc_num.max_pause = pause;

src/gc.h

@@ -69,7 +69,6 @@ typedef struct {
  uint64_t freecall;
  uint64_t total_time;
  uint64_t total_allocd;
- uint64_t since_sweep;
  size_t interval;
  int pause;
  int full_sweep;