HPA: Make dehugification threshold configurable.

include/jemalloc/internal/hpa_opts.h

@@ -20,6 +20,11 @@ struct hpa_shard_opts_s {
 	 * hugification_threshold, we force hugify it.
 	 */
 	size_t hugification_threshold;
+	/*
+	 * When the number of dirty bytes in a hugepage is >=
+	 * dehugification_threshold, we force dehugify it.
+	 */
+	size_t dehugification_threshold;
 };
 
 #define HPA_SHARD_OPTS_DEFAULT {					\
@@ -27,6 +32,8 @@ struct hpa_shard_opts_s {
 	64 * 1024,							\
 	/* hugification_threshold */					\
 	HUGEPAGE * 95 / 100,						\
+	/* dehugification_threshold */					\
+	HUGEPAGE * 20 / 100						\
 }
 
 #endif /* JEMALLOC_INTERNAL_HPA_OPTS_H */

src/ctl.c

@@ -95,6 +95,7 @@ CTL_PROTO(opt_confirm_conf)
 CTL_PROTO(opt_hpa)
 CTL_PROTO(opt_hpa_slab_max_alloc)
 CTL_PROTO(opt_hpa_hugification_threshold)
+CTL_PROTO(opt_hpa_dehugification_threshold)
 CTL_PROTO(opt_hpa_sec_max_alloc)
 CTL_PROTO(opt_hpa_sec_max_bytes)
 CTL_PROTO(opt_hpa_sec_nshards)
@@ -399,6 +400,8 @@ static const ctl_named_node_t opt_node[] = {
 	{NAME("hpa_slab_max_alloc"),	CTL(opt_hpa_slab_max_alloc)},
 	{NAME("hpa_hugification_threshold"),
 		CTL(opt_hpa_hugification_threshold)},
+	{NAME("hpa_dehugification_threshold"),
+		CTL(opt_hpa_dehugification_threshold)},
 	{NAME("hpa_sec_max_alloc"),	CTL(opt_hpa_sec_max_alloc)},
 	{NAME("hpa_sec_max_bytes"),	CTL(opt_hpa_sec_max_bytes)},
 	{NAME("hpa_sec_nshards"),	CTL(opt_hpa_sec_nshards)},
@@ -2096,6 +2099,8 @@ CTL_RO_NL_GEN(opt_hpa, opt_hpa, bool)
 CTL_RO_NL_GEN(opt_hpa_slab_max_alloc, opt_hpa_opts.slab_max_alloc, size_t)
 CTL_RO_NL_GEN(opt_hpa_hugification_threshold,
     opt_hpa_opts.hugification_threshold, size_t)
+CTL_RO_NL_GEN(opt_hpa_dehugification_threshold,
+    opt_hpa_opts.dehugification_threshold, size_t)
 CTL_RO_NL_GEN(opt_hpa_sec_max_alloc, opt_hpa_sec_max_alloc, size_t)
 CTL_RO_NL_GEN(opt_hpa_sec_max_bytes, opt_hpa_sec_max_bytes, size_t)
 CTL_RO_NL_GEN(opt_hpa_sec_nshards, opt_hpa_sec_nshards, size_t)

src/hpa.c

@@ -191,7 +191,9 @@ hpa_update_purge_hugify_eligibility(hpa_shard_t *shard, hpdata_t *ps) {
 	 * active pages; i.e. 4/5s of hugepage pages must be active.
 	 */
 	if ((!hpdata_huge_get(ps) && hpdata_ndirty_get(ps) > 0)
-	    || hpdata_ndirty_get(ps) > HUGEPAGE_PAGES / 5) {
+	    || (hpdata_ndirty_get(ps) != 0
+	    && hpdata_ndirty_get(ps) * PAGE
+	    >= shard->opts.dehugification_threshold)) {
 		hpdata_purge_allowed_set(ps, true);
 	}
 	if (hpa_good_hugification_candidate(shard, ps)

src/jemalloc.c

@@ -1437,6 +1437,27 @@ malloc_conf_init_helper(sc_data_t *sc_data, unsigned bin_shard_sizes[SC_NBINS],
 				CONF_CONTINUE;
 			}
 
+			/* And the same for the dehugification_threhsold. */
+			CONF_HANDLE_SIZE_T(
+			    opt_hpa_opts.dehugification_threshold,
+			    "hpa_dehugification_threshold", PAGE, HUGEPAGE,
+			    CONF_CHECK_MIN, CONF_CHECK_MAX, true);
+			if (CONF_MATCH("hpa_dehugification_threshold_ratio")) {
+				fxp_t ratio;
+				char *end;
+				bool err = fxp_parse(&ratio, v,
+				    &end);
+				if (err || (size_t)(end - v) != vlen
+				    || ratio > FXP_INIT_INT(1)) {
+					CONF_ERROR("Invalid conf value",
+					    k, klen, v, vlen);
+				} else {
+					opt_hpa_opts.dehugification_threshold =
+					    fxp_mul_frac(HUGEPAGE, ratio);
+				}
+				CONF_CONTINUE;
+			}
+
 			CONF_HANDLE_SIZE_T(opt_hpa_sec_max_alloc, "hpa_sec_max_alloc",
 			    PAGE, 0, CONF_CHECK_MIN, CONF_DONT_CHECK_MAX, true);
 			CONF_HANDLE_SIZE_T(opt_hpa_sec_max_bytes, "hpa_sec_max_bytes",

src/stats.c

@@ -1465,6 +1465,7 @@ stats_general_print(emitter_t *emitter) {
 	OPT_WRITE_BOOL("hpa")
 	OPT_WRITE_SIZE_T("hpa_slab_max_alloc")
 	OPT_WRITE_SIZE_T("hpa_hugification_threshold")
+	OPT_WRITE_SIZE_T("hpa_dehugification_threshold")
 	OPT_WRITE_SIZE_T("hpa_sec_max_alloc")
 	OPT_WRITE_SIZE_T("hpa_sec_max_bytes")
 	OPT_WRITE_SIZE_T("hpa_sec_nshards")