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Put off major collections to improve GC times. (#44215)
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* Updated GC Heuristics to avoid a full GC unless absolutely necessary.
This helps with #40644 and other programs which suffer from non-productive full collections.
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Christine Flood authored Mar 9, 2022
1 parent 4d04294 commit 80346c1
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Showing 3 changed files with 45 additions and 37 deletions.
16 changes: 16 additions & 0 deletions src/gc-debug.c
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Original file line number Diff line number Diff line change
Expand Up @@ -977,6 +977,22 @@ void gc_time_sweep_pause(uint64_t gc_end_t, int64_t actual_allocd,
jl_ns2ms(gc_postmark_end - gc_premark_end),
sweep_full ? "full" : "quick", -gc_num.allocd / 1024);
}

void gc_time_summary(int sweep_full, uint64_t start, uint64_t end,
uint64_t freed, uint64_t live, uint64_t interval,
uint64_t pause)
{
if (sweep_full > 0)
jl_safe_printf("%ld Major collection: estimate freed = %ld
live = %ldm new interval = %ldm time = %ldms\n",
end - start, freed, live/1024/1024,
interval/1024/1024, pause/1000000 );
else
jl_safe_printf("%ld Minor collection: estimate freed = %ld live = %ldm
new interval = %ldm time = %ldms\n",
end - start, freed, live/1024/1024,
interval/1024/1024, pause/1000000 );
}
#endif

void jl_gc_debug_init(void)
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61 changes: 24 additions & 37 deletions src/gc.c
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Original file line number Diff line number Diff line change
Expand Up @@ -653,9 +653,8 @@ static int prev_sweep_full = 1;
// Full collection heuristics
static int64_t live_bytes = 0;
static int64_t promoted_bytes = 0;
static int64_t last_full_live = 0; // live_bytes after last full collection
static int64_t last_live_bytes = 0; // live_bytes at last collection
static int64_t grown_heap_age = 0; // # of collects since live_bytes grew and remained
static int64_t t_start = 0; // Time GC starts;
#ifdef __GLIBC__
// maxrss at last malloc_trim
static int64_t last_trim_maxrss = 0;
Expand Down Expand Up @@ -3140,43 +3139,23 @@ static int _jl_gc_collect(jl_ptls_t ptls, jl_gc_collection_t collection)
int nptr = 0;
for (int i = 0;i < jl_n_threads;i++)
nptr += jl_all_tls_states[i]->heap.remset_nptr;
int large_frontier = nptr*sizeof(void*) >= default_collect_interval; // many pointers in the intergen frontier => "quick" mark is not quick
// trigger a full collection if the number of live bytes doubles since the last full
// collection and then remains at least that high for a while.
if (grown_heap_age == 0) {
if (live_bytes > 2 * last_full_live)
grown_heap_age = 1;
}
else if (live_bytes >= last_live_bytes) {
grown_heap_age++;
}

// many pointers in the intergen frontier => "quick" mark is not quick
int large_frontier = nptr*sizeof(void*) >= default_collect_interval;
int sweep_full = 0;
int recollect = 0;
if ((large_frontier ||
((not_freed_enough || promoted_bytes >= gc_num.interval) &&
(promoted_bytes >= default_collect_interval || prev_sweep_full)) ||
grown_heap_age > 1) && gc_num.pause > 1) {
sweep_full = 1;
}

// update heuristics only if this GC was automatically triggered
if (collection == JL_GC_AUTO) {
if (sweep_full) {
if (large_frontier)
gc_num.interval = last_long_collect_interval;
if (not_freed_enough || large_frontier) {
if (gc_num.interval <= 2*(max_collect_interval/5)) {
gc_num.interval = 5 * (gc_num.interval / 2);
}
}
last_long_collect_interval = gc_num.interval;
if (not_freed_enough) {
gc_num.interval = gc_num.interval * 2;
}
else {
// reset interval to default, or at least half of live_bytes
int64_t half = live_bytes/2;
if (default_collect_interval < half && half <= max_collect_interval)
gc_num.interval = half;
else
gc_num.interval = default_collect_interval;
if (large_frontier) {
sweep_full = 1;
}
if (gc_num.interval > max_collect_interval) {
sweep_full = 1;
gc_num.interval = max_collect_interval;
}
}
if (gc_sweep_always_full) {
Expand Down Expand Up @@ -3249,10 +3228,17 @@ static int _jl_gc_collect(jl_ptls_t ptls, jl_gc_collection_t collection)
gc_num.allocd = 0;
last_live_bytes = live_bytes;
live_bytes += -gc_num.freed + gc_num.since_sweep;
if (prev_sweep_full) {
last_full_live = live_bytes;
grown_heap_age = 0;

if (collection == JL_GC_AUTO) {
// If the current interval is larger than half the live data decrease the interval
int64_t half = live_bytes/2;
if (gc_num.interval > half) gc_num.interval = half;
// But never go below default
if (gc_num.interval < default_collect_interval) gc_num.interval = default_collect_interval;
}

gc_time_summary(sweep_full, t_start, gc_end_t, gc_num.freed, live_bytes, gc_num.interval, pause);

prev_sweep_full = sweep_full;
gc_num.pause += !recollect;
gc_num.total_time += pause;
Expand Down Expand Up @@ -3420,6 +3406,7 @@ void jl_gc_init(void)
#endif
jl_gc_mark_sp_t sp = {NULL, NULL, NULL, NULL};
gc_mark_loop(NULL, sp);
t_start = jl_hrtime();
}

// callback for passing OOM errors from gmp
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5 changes: 5 additions & 0 deletions src/gc.h
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Original file line number Diff line number Diff line change
Expand Up @@ -557,6 +557,9 @@ void gc_time_mark_pause(int64_t t0, int64_t scanned_bytes,
void gc_time_sweep_pause(uint64_t gc_end_t, int64_t actual_allocd,
int64_t live_bytes, int64_t estimate_freed,
int sweep_full);
void gc_time_summary(int sweep_full, uint64_t start, uint64_t end,
uint64_t freed, uint64_t live, uint64_t interval,
uint64_t pause);
#else
#define gc_time_pool_start()
STATIC_INLINE void gc_time_count_page(int freedall, int pg_skpd) JL_NOTSAFEPOINT
Expand All @@ -582,6 +585,8 @@ STATIC_INLINE void gc_time_count_mallocd_array(int bits) JL_NOTSAFEPOINT
#define gc_time_mark_pause(t0, scanned_bytes, perm_scanned_bytes)
#define gc_time_sweep_pause(gc_end_t, actual_allocd, live_bytes, \
estimate_freed, sweep_full)
#define gc_time_summary(sweep_full, start, end, freed, live, \
interval, pause)
#endif

#ifdef MEMFENCE
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