From e286fba00a8e4cd71033e583f88ae35cbd914778 Mon Sep 17 00:00:00 2001
From: Slobodan Predolac <spredolac@fb.com>
Date: Thu, 30 Apr 2026 15:31:21 -0700
Subject: [PATCH] Extract bin->stats.nrequests mutation into
 bin_stats_nrequests_add

---
 include/jemalloc/internal/bin.h |  7 +++++++
 src/tcache.c                    |  5 ++---
 test/unit/bin.c                 | 37 +++++++++++++++++++++++++++++++++
 3 files changed, 46 insertions(+), 3 deletions(-)

diff --git a/include/jemalloc/internal/bin.h b/include/jemalloc/internal/bin.h
index 51d4c89e..a7eba760 100644
--- a/include/jemalloc/internal/bin.h
+++ b/include/jemalloc/internal/bin.h
@@ -100,6 +100,13 @@ bin_t *bin_choose(tsdn_t *tsdn, arena_t *arena, szind_t binind,
     unsigned *binshard_p);
 
 /* Stats. */
+static inline void
+bin_stats_nrequests_add(tsdn_t *tsdn, bin_t *bin, uint64_t n) {
+	malloc_mutex_lock(tsdn, &bin->lock);
+	bin->stats.nrequests += n;
+	malloc_mutex_unlock(tsdn, &bin->lock);
+}
+
 static inline void
 bin_stats_merge(tsdn_t *tsdn, bin_stats_data_t *dst_bin_stats, bin_t *bin) {
 	malloc_mutex_lock(tsdn, &bin->lock);
diff --git a/src/tcache.c b/src/tcache.c
index fe210d27..d1a2cfd0 100644
--- a/src/tcache.c
+++ b/src/tcache.c
@@ -1287,9 +1287,8 @@ tcache_stats_merge(tsdn_t *tsdn, tcache_t *tcache, arena_t *arena) {
 		}
 		if (i < SC_NBINS) {
 			bin_t *bin = bin_choose(tsdn, arena, i, NULL);
-			malloc_mutex_lock(tsdn, &bin->lock);
-			bin->stats.nrequests += cache_bin->tstats.nrequests;
-			malloc_mutex_unlock(tsdn, &bin->lock);
+			bin_stats_nrequests_add(tsdn, bin,
+			    cache_bin->tstats.nrequests);
 		} else {
 			arena_stats_large_flush_nrequests_add(tsdn,
 			    &arena->stats, i, cache_bin->tstats.nrequests);
diff --git a/test/unit/bin.c b/test/unit/bin.c
index 002bbf11..17365d02 100644
--- a/test/unit/bin.c
+++ b/test/unit/bin.c
@@ -647,6 +647,42 @@ TEST_BEGIN(test_bin_dalloc_slab_prepare) {
 }
 TEST_END
 
+/*
+ * Test that bin_stats_nrequests_add accumulates under the bin lock.
+ */
+TEST_BEGIN(test_bin_stats_nrequests_add) {
+	tsdn_t *tsdn = tsdn_fetch();
+	bin_t bin;
+
+	bin_init(&bin);
+	if (config_stats) {
+		expect_u64_eq(bin.stats.nrequests, 0,
+		    "Fresh bin should have zero nrequests");
+	}
+
+	/* Single add. */
+	bin_stats_nrequests_add(tsdn, &bin, 7);
+	if (config_stats) {
+		expect_u64_eq(bin.stats.nrequests, 7,
+		    "nrequests should equal the added value");
+	}
+
+	/* Adds accumulate. */
+	bin_stats_nrequests_add(tsdn, &bin, 3);
+	if (config_stats) {
+		expect_u64_eq(bin.stats.nrequests, 10,
+		    "nrequests should accumulate across calls");
+	}
+
+	/* Adding zero is a no-op. */
+	bin_stats_nrequests_add(tsdn, &bin, 0);
+	if (config_stats) {
+		expect_u64_eq(bin.stats.nrequests, 10,
+		    "Adding zero should not change nrequests");
+	}
+}
+TEST_END
+
 /*
  * Test bin_shard_sizes_boot and bin_update_shard_size.
  */
@@ -819,6 +855,7 @@ main(void) {
 	    test_bin_lower_slab_replaces_slabcur,
 	    test_bin_lower_slab_inserts_nonfull,
 	    test_bin_dalloc_slab_prepare,
+	    test_bin_stats_nrequests_add,
 	    test_bin_shard_sizes,
 	    test_bin_alloc_free_cycle,
 	    test_bin_multi_size_class);