Track the leaked VM space via the abandoned_vm counter.

The counter is 0 unless metadata allocation failed (indicates OOM), and is
mainly for sanity checking.

include/jemalloc/internal/arena_stats.h

@@ -112,6 +112,9 @@ struct arena_stats_s {
 	arena_stats_u64_t	nflushes_large; /* Derived. */
 	arena_stats_u64_t	nrequests_large; /* Derived. */
 
+	/* VM space had to be leaked (undocumented).  Normally 0. */
+	atomic_zu_t		abandoned_vm;
+
 	/* Number of bytes cached in tcache associated with this arena. */
 	atomic_zu_t		tcache_bytes; /* Derived. */
 

src/arena.c

@@ -132,6 +132,8 @@ arena_stats_merge(tsdn_t *tsdn, arena_t *arena, unsigned *nthreads,
 	    (((atomic_load_zu(&arena->nactive, ATOMIC_RELAXED) +
 	    extents_npages_get(&arena->extents_dirty) +
 	    extents_npages_get(&arena->extents_muzzy)) << LG_PAGE)));
+	arena_stats_accum_zu(&astats->abandoned_vm, atomic_load_zu(
+	    &arena->stats.abandoned_vm, ATOMIC_RELAXED));
 
 	for (szind_t i = 0; i < SC_NSIZES - SC_NBINS; i++) {
 		uint64_t nmalloc = arena_stats_read_u64(tsdn, &arena->stats,

src/ctl.c

@@ -210,6 +210,7 @@ CTL_PROTO(stats_arenas_i_internal)
 CTL_PROTO(stats_arenas_i_metadata_thp)
 CTL_PROTO(stats_arenas_i_tcache_bytes)
 CTL_PROTO(stats_arenas_i_resident)
+CTL_PROTO(stats_arenas_i_abandoned_vm)
 INDEX_PROTO(stats_arenas_i)
 CTL_PROTO(stats_allocated)
 CTL_PROTO(stats_active)
@@ -543,6 +544,7 @@ static const ctl_named_node_t stats_arenas_i_node[] = {
 	{NAME("metadata_thp"),	CTL(stats_arenas_i_metadata_thp)},
 	{NAME("tcache_bytes"),	CTL(stats_arenas_i_tcache_bytes)},
 	{NAME("resident"),	CTL(stats_arenas_i_resident)},
+	{NAME("abandoned_vm"),	CTL(stats_arenas_i_abandoned_vm)},
 	{NAME("small"),		CHILD(named, stats_arenas_i_small)},
 	{NAME("large"),		CHILD(named, stats_arenas_i_large)},
 	{NAME("bins"),		CHILD(indexed, stats_arenas_i_bins)},
@@ -913,6 +915,8 @@ MUTEX_PROF_ARENA_MUTEXES
 		    &astats->astats.ndalloc_large);
 		ctl_accum_arena_stats_u64(&sdstats->astats.nrequests_large,
 		    &astats->astats.nrequests_large);
+		accum_atomic_zu(&sdstats->astats.abandoned_vm,
+		    &astats->astats.abandoned_vm);
 
 		accum_atomic_zu(&sdstats->astats.tcache_bytes,
 		    &astats->astats.tcache_bytes);
@@ -2871,6 +2875,9 @@ CTL_RO_CGEN(config_stats, stats_arenas_i_tcache_bytes,
 CTL_RO_CGEN(config_stats, stats_arenas_i_resident,
     atomic_load_zu(&arenas_i(mib[2])->astats->astats.resident, ATOMIC_RELAXED),
     size_t)
+CTL_RO_CGEN(config_stats, stats_arenas_i_abandoned_vm,
+    atomic_load_zu(&arenas_i(mib[2])->astats->astats.abandoned_vm,
+    ATOMIC_RELAXED), size_t)
 
 CTL_RO_CGEN(config_stats, stats_arenas_i_small_allocated,
     arenas_i(mib[2])->astats->allocated_small, size_t)

src/extent.c

@@ -619,16 +619,24 @@ label_return:
 	return extent;
 }
 
+/*
+ * This can only happen when we fail to allocate a new extent struct (which
+ * indicates OOM), e.g. when trying to split an existing extent.
+ */
 static void
-extents_leak(tsdn_t *tsdn, arena_t *arena, extent_hooks_t **r_extent_hooks,
+extents_abandon_vm(tsdn_t *tsdn, arena_t *arena, extent_hooks_t **r_extent_hooks,
     extents_t *extents, extent_t *extent, bool growing_retained) {
+	size_t sz = extent_size_get(extent);
+	if (config_stats) {
+		arena_stats_accum_zu(&arena->stats.abandoned_vm, sz);
+	}
 	/*
 	 * Leak extent after making sure its pages have already been purged, so
 	 * that this is only a virtual memory leak.
 	 */
 	if (extents_state_get(extents) == extent_state_dirty) {
 		if (extent_purge_lazy_impl(tsdn, arena, r_extent_hooks,
-		    extent, 0, extent_size_get(extent), growing_retained)) {
+		    extent, 0, sz, growing_retained)) {
 			extent_purge_forced_impl(tsdn, arena, r_extent_hooks,
 			    extent, 0, extent_size_get(extent),
 			    growing_retained);
@@ -1083,7 +1091,7 @@ extent_recycle_split(tsdn_t *tsdn, arena_t *arena,
 		if (to_leak != NULL) {
 			void *leak = extent_base_get(to_leak);
 			extent_deregister_no_gdump_sub(tsdn, to_leak);
-			extents_leak(tsdn, arena, r_extent_hooks, extents,
+			extents_abandon_vm(tsdn, arena, r_extent_hooks, extents,
 			    to_leak, growing_retained);
 			assert(extent_lock_from_addr(tsdn, rtree_ctx, leak,
 			    false) == NULL);
@@ -1382,7 +1390,7 @@ extent_grow_retained(tsdn_t *tsdn, arena_t *arena,
 		}
 		if (to_leak != NULL) {
 			extent_deregister_no_gdump_sub(tsdn, to_leak);
-			extents_leak(tsdn, arena, r_extent_hooks,
+			extents_abandon_vm(tsdn, arena, r_extent_hooks,
 			    &arena->extents_retained, to_leak, true);
 		}
 		goto label_err;

src/stats.c

@@ -673,7 +673,7 @@ stats_arena_print(emitter_t *emitter, unsigned i, bool bins, bool large,
 	size_t large_allocated;
 	uint64_t large_nmalloc, large_ndalloc, large_nrequests, large_nfills,
 	    large_nflushes;
-	size_t tcache_bytes;
+	size_t tcache_bytes, abandoned_vm;
 	uint64_t uptime;
 
 	CTL_GET("arenas.page", &page, size_t);
@@ -963,6 +963,7 @@ stats_arena_print(emitter_t *emitter, unsigned i, bool bins, bool large,
 	GET_AND_EMIT_MEM_STAT(metadata_thp)
 	GET_AND_EMIT_MEM_STAT(tcache_bytes)
 	GET_AND_EMIT_MEM_STAT(resident)
+	GET_AND_EMIT_MEM_STAT(abandoned_vm)
 	GET_AND_EMIT_MEM_STAT(extent_avail)
 #undef GET_AND_EMIT_MEM_STAT