Refactor deferral constants into corresponding headers.

Currently there are deferral-relevant constants in arena.c and
background_thread.c. This commit moves them out into corresponding PAC
and HPA headers. Those commonly needed by both are put into a new header
deferral.h where the contract of deferral are clearly stated.

include/jemalloc/internal/arena.h

@@ -177,12 +177,6 @@ struct arena_s {
 /* EXTERNS */
 /******************************************************************************/
 
-/*
- * When the amount of pages to be purged exceeds this amount, deferred purge
- * should happen.
- */
-#define ARENA_DEFERRED_PURGE_NPAGES_THRESHOLD UINT64_C(1024)
-
 extern ssize_t opt_dirty_decay_ms;
 extern ssize_t opt_muzzy_decay_ms;
 

include/jemalloc/internal/background_thread.h

@@ -13,17 +13,6 @@
 #define MAX_BACKGROUND_THREAD_LIMIT MALLOCX_ARENA_LIMIT
 #define DEFAULT_NUM_BACKGROUND_THREAD 4
 
-/*
- * These exist only as a transitional state.  Eventually, deferral should be
- * part of the PAI, and each implementation can indicate wait times with more
- * specificity.
- */
-#define BACKGROUND_THREAD_HPA_INTERVAL_MAX_UNINITIALIZED (-2)
-#define BACKGROUND_THREAD_HPA_INTERVAL_MAX_DEFAULT_WHEN_ENABLED 5000
-
-#define BACKGROUND_THREAD_DEFERRED_MIN UINT64_C(0)
-#define BACKGROUND_THREAD_DEFERRED_MAX UINT64_MAX
-
 typedef enum {
 	background_thread_stopped,
 	background_thread_started,

include/jemalloc/internal/deferral.h

@@ -0,0 +1,30 @@
+#ifndef JEMALLOC_INTERNAL_DEFERRAL_H
+#define JEMALLOC_INTERNAL_DEFERRAL_H
+
+#include "jemalloc/internal/jemalloc_preamble.h"
+
+/*
+ * The deferred-work contract shared by the page allocators that PRODUCE
+ * deferred work (PAC decay-purge, HPA purge/hugify) and the drivers that
+ * CONSUME it (the background thread, or the application-inline fallback).
+ *
+ * There is deliberately no polymorphic interface here: with only two
+ * page allocators, a vtable's indirect calls are needless and inefficient.
+ * Dispatch is direct pac_*()/hpa_*(), so the contract is a convention
+ * documented here, not an enforced type.  The only shared code it needs is the
+ * constants below; each allocator keeps its own policy definition (functions
+ * and constants) in its own header.
+ *
+ * The convention every page allocator follows:
+ *   - <alloc>_time_until_deferred_work(): nanoseconds until its next
+ *     deferred work is due.  DEFERRED_WORK_MIN = "due now",
+ *     DEFERRED_WORK_MAX = "nothing pending"; anything between is a real
+ *     ns deadline.
+ *   - <alloc>_do_deferred_work(): perform whatever work is due now.
+ * The pa layer reports the soonest deadline across its allocators; the
+ * background thread sleeps until then, or indefinitely on DEFERRED_WORK_MAX.
+ */
+#define DEFERRED_WORK_MIN UINT64_C(0)
+#define DEFERRED_WORK_MAX UINT64_MAX
+
+#endif /* JEMALLOC_INTERNAL_DEFERRAL_H */

include/jemalloc/internal/hpa.h

@@ -13,6 +13,14 @@
 #include "jemalloc/internal/psset.h"
 #include "jemalloc/internal/sec.h"
 
+/*
+ * HPA-specific deferral interval bounds (currently unused).  Deferral tuning
+ * is per-allocator policy, so it lives in the HPA header; see deferral.h for
+ * the shared deferred-work contract.
+ */
+#define HPA_INTERVAL_MAX_UNINITIALIZED (-2)
+#define HPA_INTERVAL_MAX_DEFAULT_WHEN_ENABLED 5000
+
 typedef struct hpa_shard_nonderived_stats_s hpa_shard_nonderived_stats_t;
 struct hpa_shard_nonderived_stats_s {
 	/*

include/jemalloc/internal/pac.h

@@ -13,7 +13,7 @@
 #include "san_bump.h"
 
 /*
- * Page allocator classic; an implementation of the PAI interface that:
+ * Page allocator classic (PAC), a page-level allocator that:
  * - Can be used for arenas with custom extent hooks.
  * - Can always satisfy any allocation request (including highly-fragmentary
  *   ones).
@@ -28,6 +28,14 @@ enum pac_purge_eagerness_e {
 };
 typedef enum pac_purge_eagerness_e pac_purge_eagerness_t;
 
+/*
+ * When a decay sweep would purge more than this many pages, its purge is
+ * treated as due (worth waking the background thread for) instead of left
+ * to accumulate.  PAC decay policy; the HPA defers on time intervals, not
+ * on a page count, so this constant is PAC-only.
+ */
+#define PAC_DECAY_PURGE_NPAGES_THRESHOLD UINT64_C(1024)
+
 typedef struct pac_decay_stats_s pac_decay_stats_t;
 struct pac_decay_stats_s {
 	/* Total number of purge sweeps. */

src/arena.c

@@ -595,7 +595,7 @@ arena_should_decay_early(tsdn_t *tsdn, arena_t *arena, decay_t *decay,
 	}
 	malloc_mutex_unlock(tsdn, &decay->mtx);
 	return info->npages_to_purge_new
-	    > ARENA_DEFERRED_PURGE_NPAGES_THRESHOLD;
+	    > PAC_DECAY_PURGE_NPAGES_THRESHOLD;
 }
 
 /*

src/background_thread.c

@@ -6,6 +6,7 @@
 #include "jemalloc/internal/background_thread.h"
 #include "jemalloc/internal/background_thread_inlines.h"
 #include "jemalloc/internal/ctl.h"
+#include "jemalloc/internal/deferral.h"
 #include "jemalloc/internal/jemalloc_internal_inlines_a.h"
 #include "jemalloc/internal/malloc_io.h"
 #include "jemalloc/internal/mutex.h"
@@ -262,7 +263,7 @@ background_thread_pause_check(tsdn_t *tsdn, background_thread_info_t *info) {
 static inline void
 background_work_sleep_once(
     tsdn_t *tsdn, background_thread_info_t *info, unsigned ind) {
-	uint64_t ns_until_deferred = BACKGROUND_THREAD_DEFERRED_MAX;
+	uint64_t ns_until_deferred = DEFERRED_WORK_MAX;
 	unsigned narenas = narenas_total_get();
 	bool     slept_indefinitely = background_thread_indefinite_sleep(info);
 
@@ -291,7 +292,7 @@ background_work_sleep_once(
 	}
 
 	uint64_t sleep_ns;
-	if (ns_until_deferred == BACKGROUND_THREAD_DEFERRED_MAX) {
+	if (ns_until_deferred == DEFERRED_WORK_MAX) {
 		sleep_ns = BACKGROUND_THREAD_INDEFINITE_SLEEP;
 	} else {
 		sleep_ns = (ns_until_deferred

src/hpa.c

@@ -1,6 +1,7 @@
 #include "jemalloc/internal/jemalloc_preamble.h"
 
 #include "jemalloc/internal/background_thread.h"
+#include "jemalloc/internal/deferral.h"
 #include "jemalloc/internal/hpa.h"
 #include "jemalloc/internal/hpa_utils.h"
 #include "jemalloc/internal/jemalloc_probe.h"
@@ -1081,7 +1082,7 @@ hpa_dalloc(tsdn_t *tsdn, hpa_shard_t *shard, edata_t *edata,
  */
 uint64_t
 hpa_time_until_deferred_work(tsdn_t *tsdn, hpa_shard_t *shard) {
-	uint64_t time_ns = BACKGROUND_THREAD_DEFERRED_MAX;
+	uint64_t time_ns = DEFERRED_WORK_MAX;
 
 	malloc_mutex_lock(tsdn, &shard->mtx);
 
@@ -1101,7 +1102,7 @@ hpa_time_until_deferred_work(tsdn_t *tsdn, hpa_shard_t *shard) {
 			time_ns *= 1000 * 1000;
 		} else {
 			malloc_mutex_unlock(tsdn, &shard->mtx);
-			return BACKGROUND_THREAD_DEFERRED_MIN;
+			return DEFERRED_WORK_MIN;
 		}
 	}
 
@@ -1112,7 +1113,7 @@ hpa_time_until_deferred_work(tsdn_t *tsdn, hpa_shard_t *shard) {
 		 */
 		if (shard->stats.npurge_passes == 0) {
 			malloc_mutex_unlock(tsdn, &shard->mtx);
-			return BACKGROUND_THREAD_DEFERRED_MIN;
+			return DEFERRED_WORK_MIN;
 		}
 		uint64_t since_last_purge_ms = shard->central->hooks.ms_since(
 		    &shard->last_purge);
@@ -1127,7 +1128,7 @@ hpa_time_until_deferred_work(tsdn_t *tsdn, hpa_shard_t *shard) {
 				time_ns = until_purge_ns;
 			}
 		} else {
-			time_ns = BACKGROUND_THREAD_DEFERRED_MIN;
+			time_ns = DEFERRED_WORK_MIN;
 		}
 	}
 	malloc_mutex_unlock(tsdn, &shard->mtx);

src/pa.c

@@ -1,6 +1,7 @@
 #include "jemalloc/internal/jemalloc_preamble.h"
 
 #include "jemalloc/internal/background_thread.h"
+#include "jemalloc/internal/deferral.h"
 #include "jemalloc/internal/hpa.h"
 #include "jemalloc/internal/pa.h"
 
@@ -272,7 +273,7 @@ pa_shard_do_deferred_work(
 uint64_t
 pa_shard_time_until_deferred_work(tsdn_t *tsdn, pa_shard_t *shard) {
 	uint64_t time = pac_time_until_deferred_work(tsdn, &shard->pac);
-	if (time == BACKGROUND_THREAD_DEFERRED_MIN) {
+	if (time == DEFERRED_WORK_MIN) {
 		return time;
 	}
 

src/pac.c

@@ -2,6 +2,7 @@
 
 #include "jemalloc/internal/arena.h"
 #include "jemalloc/internal/background_thread.h"
+#include "jemalloc/internal/deferral.h"
 #include "jemalloc/internal/extent.h"
 #include "jemalloc/internal/pac.h"
 #include "jemalloc/internal/san.h"
@@ -482,10 +483,10 @@ static inline uint64_t
 pac_ns_until_purge(tsdn_t *tsdn, decay_t *decay, size_t npages) {
 	if (malloc_mutex_trylock(tsdn, &decay->mtx)) {
 		/* Use minimal interval if decay is contended. */
-		return BACKGROUND_THREAD_DEFERRED_MIN;
+		return DEFERRED_WORK_MIN;
 	}
 	uint64_t result = decay_ns_until_purge(
-	    decay, npages, ARENA_DEFERRED_PURGE_NPAGES_THRESHOLD);
+	    decay, npages, PAC_DECAY_PURGE_NPAGES_THRESHOLD);
 
 	malloc_mutex_unlock(tsdn, &decay->mtx);
 	return result;
@@ -497,7 +498,7 @@ pac_time_until_deferred_work(tsdn_t *tsdn, pac_t *pac) {
 
 	time = pac_ns_until_purge(
 	    tsdn, &pac->decay_dirty, ecache_npages_get(&pac->ecache_dirty));
-	if (time == BACKGROUND_THREAD_DEFERRED_MIN) {
+	if (time == DEFERRED_WORK_MIN) {
 		return time;
 	}
 

test/unit/hpa.c

@@ -1,5 +1,6 @@
 #include "test/jemalloc_test.h"
 
+#include "jemalloc/internal/deferral.h"
 #include "jemalloc/internal/hpa.h"
 #include "jemalloc/internal/nstime.h"
 
@@ -1131,14 +1132,14 @@ TEST_BEGIN(test_deferred_until_time) {
 	/* Current time = 900ms, purge_eligible at 1300ms */
 	nstime_init(&defer_curtime, 900UL * 1000 * 1000);
 	uint64_t until_ns = hpa_time_until_deferred_work(tsdn, shard);
-	expect_u64_eq(until_ns, BACKGROUND_THREAD_DEFERRED_MIN,
+	expect_u64_eq(until_ns, DEFERRED_WORK_MIN,
 	    "First pass did not happen");
 
 	/* Fake that first pass happened more than min_purge_interval_ago */
 	nstime_init(&shard->last_purge, 350UL * 1000 * 1000);
 	shard->stats.npurge_passes = 1;
 	until_ns = hpa_time_until_deferred_work(tsdn, shard);
-	expect_u64_eq(until_ns, BACKGROUND_THREAD_DEFERRED_MIN,
+	expect_u64_eq(until_ns, DEFERRED_WORK_MIN,
 	    "No need to heck anything it is more than interval");
 
 	nstime_init(&shard->last_purge, 900UL * 1000 * 1000);