From a787d2f5b35f8a28738e19efeea626c2a3999104 Mon Sep 17 00:00:00 2001
From: Qi Wang <interwq@gwu.edu>
Date: Fri, 8 Nov 2019 13:05:43 -0800
Subject: [PATCH] Prefer getaffinity() to detect number of CPUs.

---
 src/jemalloc.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/src/jemalloc.c b/src/jemalloc.c
index 239494df..0e379d42 100644
--- a/src/jemalloc.c
+++ b/src/jemalloc.c
@@ -742,18 +742,28 @@ malloc_ncpus(void) {
 	SYSTEM_INFO si;
 	GetSystemInfo(&si);
 	result = si.dwNumberOfProcessors;
-#elif defined(JEMALLOC_GLIBC_MALLOC_HOOK) && defined(CPU_COUNT)
+#elif defined(CPU_COUNT)
 	/*
 	 * glibc >= 2.6 has the CPU_COUNT macro.
 	 *
 	 * glibc's sysconf() uses isspace().  glibc allocates for the first time
 	 * *before* setting up the isspace tables.  Therefore we need a
 	 * different method to get the number of CPUs.
+	 *
+	 * The getaffinity approach is also preferred when only a subset of CPUs
+	 * is available, to avoid using more arenas than necessary.
 	 */
 	{
+#  if defined(__FreeBSD__)
+		cpuset_t set;
+#  else
 		cpu_set_t set;
-
+#  endif
+#  if defined(JEMALLOC_HAVE_SCHED_SETAFFINITY)
+		sched_getaffinity(0, sizeof(set), &set);
+#  else
 		pthread_getaffinity_np(pthread_self(), sizeof(set), &set);
+#  endif
 		result = CPU_COUNT(&set);
 	}
 #else