Add HPA deferral functionality.

include/jemalloc/internal/arena_externs.h

@@ -51,6 +51,7 @@ bool arena_decay_ms_set(tsdn_t *tsdn, arena_t *arena, extent_state_t state,
 ssize_t arena_decay_ms_get(arena_t *arena, extent_state_t state);
 void arena_decay(tsdn_t *tsdn, arena_t *arena, bool is_background_thread,
     bool all);
+void arena_do_deferred_work(tsdn_t *tsdn, arena_t *arena);
 void arena_reset(tsd_t *tsd, arena_t *arena);
 void arena_destroy(tsd_t *tsd, arena_t *arena);
 void arena_cache_bin_fill_small(tsdn_t *tsdn, arena_t *arena,

include/jemalloc/internal/hpa.h

@@ -55,6 +55,7 @@ struct hpa_shard_s {
 	malloc_mutex_t mtx;
 	/* The base metadata allocator. */
 	base_t *base;
+
 	/*
 	 * This edata cache is the one we use when allocating a small extent
 	 * from a pageslab.  The pageslab itself comes from the centralized
@@ -122,6 +123,10 @@ void hpa_shard_stats_merge(tsdn_t *tsdn, hpa_shard_t *shard,
 void hpa_shard_disable(tsdn_t *tsdn, hpa_shard_t *shard);
 void hpa_shard_destroy(tsdn_t *tsdn, hpa_shard_t *shard);
 
+void hpa_shard_set_deferral_allowed(tsdn_t *tsdn, hpa_shard_t *shard,
+    bool deferral_allowed);
+void hpa_shard_do_deferred_work(tsdn_t *tsdn, hpa_shard_t *shard);
+
 /*
  * We share the fork ordering with the PA and arena prefork handling; that's why
  * these are 3 and 4 rather than 0 and 1.

include/jemalloc/internal/hpa_opts.h

@@ -32,6 +32,14 @@ struct hpa_shard_opts_s {
 	 * active_pages.  This may be set to (fxp_t)-1 to disable purging.
 	 */
 	fxp_t dirty_mult;
+
+	/*
+	 * Whether or not the PAI methods are allowed to defer work to a
+	 * subsequent hpa_shard_do_deferred_work() call.  Practically, this
+	 * corresponds to background threads being enabled.  We track this
+	 * ourselves for encapsulation purposes.
+	 */
+	bool deferral_allowed;
 };
 
 #define HPA_SHARD_OPTS_DEFAULT {					\
@@ -42,7 +50,15 @@ struct hpa_shard_opts_s {
 	/* dehugification_threshold */					\
 	HUGEPAGE * 20 / 100,						\
 	/* dirty_mult */						\
-	FXP_INIT_PERCENT(25)						\
+	FXP_INIT_PERCENT(25),						\
+	/*								\
+	 * deferral_allowed						\
+	 * 								\
+	 * Really, this is always set by the arena during creation	\
+	 * or by an hpa_shard_set_deferral_allowed call, so the value	\
+	 * we put here doesn't matter.					\
+	 */								\
+	false								\
 }
 
 #endif /* JEMALLOC_INTERNAL_HPA_OPTS_H */

src/arena.c

@@ -461,6 +461,12 @@ arena_decay(tsdn_t *tsdn, arena_t *arena, bool is_background_thread, bool all) {
 	arena_decay_muzzy(tsdn, arena, is_background_thread, all);
 }
 
+/* Called from background threads. */
+void
+arena_do_deferred_work(tsdn_t *tsdn, arena_t *arena) {
+	arena_decay(tsdn, arena, true, false);
+}
+
 void
 arena_slab_dalloc(tsdn_t *tsdn, arena_t *arena, edata_t *slab) {
 	bool generated_dirty;
@@ -1565,7 +1571,9 @@ arena_new(tsdn_t *tsdn, unsigned ind, extent_hooks_t *extent_hooks) {
 	 *   so arena_hpa_global is not yet initialized.
 	 */
 	if (opt_hpa && ehooks_are_default(base_ehooks_get(base)) && ind != 0) {
-		if (pa_shard_enable_hpa(tsdn, &arena->pa_shard, &opt_hpa_opts,
+		hpa_shard_opts_t hpa_shard_opts = opt_hpa_opts;
+		hpa_shard_opts.deferral_allowed = background_thread_enabled();
+		if (pa_shard_enable_hpa(tsdn, &arena->pa_shard, &hpa_shard_opts,
 		    &opt_hpa_sec_opts)) {
 			goto label_error;
 		}

src/background_thread.c

@@ -291,7 +291,7 @@ background_work_sleep_once(tsdn_t *tsdn, background_thread_info_t *info, unsigne
 		if (!arena) {
 			continue;
 		}
-		arena_decay(tsdn, arena, true, false);
+		arena_do_deferred_work(tsdn, arena);
 		if (min_interval == BACKGROUND_THREAD_MIN_INTERVAL_NS) {
 			/* Min interval will be used. */
 			continue;

src/hpa.c

@@ -426,17 +426,29 @@ hpa_try_hugify(tsdn_t *tsdn, hpa_shard_t *shard) {
 	return true;
 }
 
+/*
+ * Execution of deferred work is forced if it's triggered by an explicit
+ * hpa_shard_do_deferred_work() call.
+ */
 static void
-hpa_do_deferred_work(tsdn_t *tsdn, hpa_shard_t *shard) {
+hpa_shard_maybe_do_deferred_work(tsdn_t *tsdn, hpa_shard_t *shard,
+    bool forced) {
 	bool hugified;
 	bool purged;
 	size_t nloop = 0;
-	/* Just *some* bound, to impose a worst-case latency bound. */
-	size_t maxloops = 100;;
+	malloc_mutex_assert_owner(tsdn, &shard->mtx);
+	if (!forced && shard->opts.deferral_allowed) {
+		return;
+	}
+	/*
+	 * If we're on a background thread, do work so long as there's work to
+	 * be done.  Otherwise, bound latency to not be *too* bad by doing at
+	 * most a small fixed number of operations.
+	 */
+	size_t maxloops = (forced ? (size_t)-1 : 8);
 	do {
-		malloc_mutex_assert_owner(tsdn, &shard->mtx);
 		hugified = hpa_try_hugify(tsdn, shard);
-
+		malloc_mutex_assert_owner(tsdn, &shard->mtx);
 		purged = false;
 		if (hpa_should_purge(tsdn, shard)) {
 			purged = hpa_try_purge(tsdn, shard);
@@ -528,7 +540,7 @@ hpa_try_alloc_batch_no_grow(tsdn_t *tsdn, hpa_shard_t *shard, size_t size,
 		edata_list_active_append(results, edata);
 	}
 
-	hpa_do_deferred_work(tsdn, shard);
+	hpa_shard_maybe_do_deferred_work(tsdn, shard, /* forced */ false);
 	malloc_mutex_unlock(tsdn, &shard->mtx);
 	return nsuccess;
 }
@@ -740,7 +752,7 @@ hpa_dalloc_batch(tsdn_t *tsdn, pai_t *self, edata_list_active_t *list) {
 		edata_list_active_remove(list, edata);
 		hpa_dalloc_locked(tsdn, shard, edata);
 	}
-	hpa_do_deferred_work(tsdn, shard);
+	hpa_shard_maybe_do_deferred_work(tsdn, shard, /* forced */ false);
 	malloc_mutex_unlock(tsdn, &shard->mtx);
 }
 
@@ -800,6 +812,26 @@ hpa_shard_destroy(tsdn_t *tsdn, hpa_shard_t *shard) {
 	}
 }
 
+void
+hpa_shard_set_deferral_allowed(tsdn_t *tsdn, hpa_shard_t *shard,
+    bool deferral_allowed) {
+	malloc_mutex_lock(tsdn, &shard->mtx);
+	bool deferral_previously_allowed = shard->opts.deferral_allowed;
+	shard->opts.deferral_allowed = deferral_allowed;
+	if (deferral_previously_allowed && !deferral_allowed) {
+		hpa_shard_maybe_do_deferred_work(tsdn, shard,
+		    /* forced */ true);
+	}
+	malloc_mutex_unlock(tsdn, &shard->mtx);
+}
+
+void
+hpa_shard_do_deferred_work(tsdn_t *tsdn, hpa_shard_t *shard) {
+	malloc_mutex_lock(tsdn, &shard->mtx);
+	hpa_shard_maybe_do_deferred_work(tsdn, shard, /* forced */ true);
+	malloc_mutex_unlock(tsdn, &shard->mtx);
+}
+
 void
 hpa_shard_prefork3(tsdn_t *tsdn, hpa_shard_t *shard) {
 	malloc_mutex_prefork(tsdn, &shard->grow_mtx);

src/jemalloc.c

@@ -1788,8 +1788,10 @@ malloc_init_hard_a0_locked() {
 			opt_hpa = false;
 		}
 	} else if (opt_hpa) {
-		if (pa_shard_enable_hpa(TSDN_NULL, &a0->pa_shard, &opt_hpa_opts,
-		    &opt_hpa_sec_opts)) {
+		hpa_shard_opts_t hpa_shard_opts = opt_hpa_opts;
+		hpa_shard_opts.deferral_allowed = background_thread_enabled();
+		if (pa_shard_enable_hpa(TSDN_NULL, &a0->pa_shard,
+		    &hpa_shard_opts, &opt_hpa_sec_opts)) {
 			return true;
 		}
 	}