Option to guard hpa_min_purge_interval_ms fix

Change in `hpa_min_purge_interval_ms` handling logic is not backward
compatible as it might increase memory usage. Now this logic guarded by
`hpa_strict_min_purge_interval` option.

When `hpa_strict_min_purge_interval` is true, we will purge no more than
`hpa_min_purge_interval_ms`. When `hpa_strict_min_purge_interval` is
false, old purging logic behaviour is preserved.

Long term strategy migrate all users of hpa to new logic and then delete
`hpa_strict_min_purge_interval` option.

include/jemalloc/internal/hpa_opts.h

@@ -49,6 +49,14 @@ struct hpa_shard_opts_s {
 	 * Minimum amount of time between purges.
 	 */
 	uint64_t min_purge_interval_ms;
+
+	/*
+	 * Strictly respect minimum amout of time between purges.
+	 *
+	 * This is an option to provide backward compatibility for staged rollout of
+	 * purging logic fix.
+	 */
+	bool strict_min_purge_interval;
 };
 
 #define HPA_SHARD_OPTS_DEFAULT {					\
@@ -69,7 +77,9 @@ struct hpa_shard_opts_s {
 	/* hugify_delay_ms */						\
 	10 * 1000,							\
 	/* min_purge_interval_ms */					\
-	5 * 1000							\
+	5 * 1000,							\
+	/* strict_min_purge_interval */					\
+	false								\
 }
 
 #endif /* JEMALLOC_INTERNAL_HPA_OPTS_H */

src/ctl.c

@@ -103,6 +103,7 @@ CTL_PROTO(opt_hpa_slab_max_alloc)
 CTL_PROTO(opt_hpa_hugification_threshold)
 CTL_PROTO(opt_hpa_hugify_delay_ms)
 CTL_PROTO(opt_hpa_min_purge_interval_ms)
+CTL_PROTO(opt_hpa_strict_min_purge_interval)
 CTL_PROTO(opt_hpa_dirty_mult)
 CTL_PROTO(opt_hpa_sec_nshards)
 CTL_PROTO(opt_hpa_sec_max_alloc)
@@ -459,6 +460,7 @@ static const ctl_named_node_t opt_node[] = {
 		CTL(opt_hpa_hugification_threshold)},
 	{NAME("hpa_hugify_delay_ms"), CTL(opt_hpa_hugify_delay_ms)},
 	{NAME("hpa_min_purge_interval_ms"), CTL(opt_hpa_min_purge_interval_ms)},
+	{NAME("hpa_strict_min_purge_interval"), CTL(opt_hpa_strict_min_purge_interval)},
 	{NAME("hpa_dirty_mult"), CTL(opt_hpa_dirty_mult)},
 	{NAME("hpa_sec_nshards"),	CTL(opt_hpa_sec_nshards)},
 	{NAME("hpa_sec_max_alloc"),	CTL(opt_hpa_sec_max_alloc)},
@@ -2193,6 +2195,8 @@ CTL_RO_NL_GEN(opt_hpa_hugification_threshold,
 CTL_RO_NL_GEN(opt_hpa_hugify_delay_ms, opt_hpa_opts.hugify_delay_ms, uint64_t)
 CTL_RO_NL_GEN(opt_hpa_min_purge_interval_ms, opt_hpa_opts.min_purge_interval_ms,
     uint64_t)
+CTL_RO_NL_GEN(opt_hpa_strict_min_purge_interval,
+    opt_hpa_opts.strict_min_purge_interval, bool)
 
 /*
  * This will have to change before we publicly document this option; fxp_t and

src/hpa.c

@@ -382,10 +382,12 @@ hpa_try_purge(tsdn_t *tsdn, hpa_shard_t *shard) {
 	 * Make sure we respect purge interval setting and don't purge
 	 * too frequently.
 	 */
-	uint64_t since_last_purge_ms = shard->central->hooks.ms_since(
-	    &shard->last_purge);
-	if (since_last_purge_ms < shard->opts.min_purge_interval_ms) {
-	     return false;
+	if (shard->opts.strict_min_purge_interval) {
+		uint64_t since_last_purge_ms = shard->central->hooks.ms_since(
+		    &shard->last_purge);
+		if (since_last_purge_ms < shard->opts.min_purge_interval_ms) {
+		     return false;
+		}
 	}
 
 	hpdata_t *to_purge = psset_pick_purge(&shard->psset);

src/jemalloc.c

@@ -1554,6 +1554,10 @@ malloc_conf_init_helper(sc_data_t *sc_data, unsigned bin_shard_sizes[SC_NBINS],
 			    "hpa_min_purge_interval_ms", 0, 0,
 			    CONF_DONT_CHECK_MIN, CONF_DONT_CHECK_MAX, false);
 
+			CONF_HANDLE_BOOL(
+			    opt_hpa_opts.strict_min_purge_interval,
+			    "hpa_strict_min_purge_interval");
+
 			if (CONF_MATCH("hpa_dirty_mult")) {
 				if (CONF_MATCH_VALUE("-1")) {
 					opt_hpa_opts.dirty_mult = (fxp_t)-1;

src/stats.c

@@ -1564,6 +1564,7 @@ stats_general_print(emitter_t *emitter) {
 	OPT_WRITE_SIZE_T("hpa_hugification_threshold")
 	OPT_WRITE_UINT64("hpa_hugify_delay_ms")
 	OPT_WRITE_UINT64("hpa_min_purge_interval_ms")
+	OPT_WRITE_BOOL("hpa_strict_min_purge_interval")
 	if (je_mallctl("opt.hpa_dirty_mult", (void *)&u32v, &u32sz, NULL, 0)
 	    == 0) {
 		/*

test/unit/hpa_background_thread.sh

@@ -1,4 +1,4 @@
 #!/bin/sh
 
-export MALLOC_CONF="hpa_dirty_mult:0.001,hpa_hugification_threshold_ratio:1.0,hpa_min_purge_interval_ms:50,hpa_sec_nshards:0"
+export MALLOC_CONF="hpa_dirty_mult:0.001,hpa_hugification_threshold_ratio:1.0,hpa_min_purge_interval_ms:50,hpa_strict_min_purge_interval:true,hpa_sec_nshards:0"