From d73de95f722247a56b5266a27267cd24668081e9 Mon Sep 17 00:00:00 2001
From: Slobodan Predolac <spredolac@fb.com>
Date: Wed, 4 Jun 2025 09:48:14 -0700
Subject: [PATCH] Experimental configuration option for fast path prefetch from
 cache_bin

---
 configure.ac                                  | 30 +++++++++++++++++++
 .../internal/jemalloc_internal_defs.h.in      |  5 ++++
 .../internal/jemalloc_internal_inlines_c.h    |  6 ++++
 3 files changed, 41 insertions(+)

diff --git a/configure.ac b/configure.ac
index c703a6d1..d9153feb 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1434,6 +1434,36 @@ if test "x$enable_experimental_smallocx" = "x1" ; then
 fi
 AC_SUBST([enable_experimental_smallocx])
 
+dnl Do not enable fastpath prefetch by default.
+AC_ARG_ENABLE([experimental_fp_prefetch],
+  [AS_HELP_STRING([--enable-experimental-fp-prefetch], [Enable experimental fastpath prefetch])],
+[if test "x$enable_experimental_fp_prefetch" = "xno" ; then
+enable_experimental_fp_prefetch="0"
+else
+  dnl Check if we have __builtin_prefetch.
+  JE_CFLAGS_SAVE()
+  JE_CFLAGS_ADD([-Werror=implicit-function-declaration])
+  JE_COMPILABLE([builtin prefetch], [], [
+void foo(void *p) { __builtin_prefetch(p, 1, 3); }
+  	],
+	[je_cv_have_builtin_prefetch])
+
+	if test "x${je_cv_have_builtin_prefetch}" = "xyes" ; then
+	   enable_experimental_fp_prefetch="1"
+	else
+	   enable_experimental_fp_prefetch="0"
+	   AC_MSG_ERROR([--enable--experimental-fp-prefetch can only be used when builtin_preftech is available])
+	fi
+   JE_CFLAGS_RESTORE()
+fi
+],
+[enable_experimental_fp_prefetch="0"]
+)
+if test "x$enable_experimental_fp_prefetch" = "x1" ; then
+  AC_DEFINE([JEMALLOC_EXPERIMENTAL_FASTPATH_PREFETCH], [ ], [ ])
+fi
+AC_SUBST([enable_experimental_fp_prefetch])
+
 dnl Do not enable profiling by default.
 AC_ARG_ENABLE([prof],
   [AS_HELP_STRING([--enable-prof], [Enable allocation profiling])],
diff --git a/include/jemalloc/internal/jemalloc_internal_defs.h.in b/include/jemalloc/internal/jemalloc_internal_defs.h.in
index 31ae2e8e..3a945ba1 100644
--- a/include/jemalloc/internal/jemalloc_internal_defs.h.in
+++ b/include/jemalloc/internal/jemalloc_internal_defs.h.in
@@ -160,6 +160,11 @@
 /* JEMALLOC_EXPERIMENTAL_SMALLOCX_API enables experimental smallocx API. */
 #undef JEMALLOC_EXPERIMENTAL_SMALLOCX_API
 
+/* JEMALLOC_EXPERIMENTAL_FASTPATH_PREFETCH enables prefetch
+ * on malloc fast path.
+ */
+#undef JEMALLOC_EXPERIMENTAL_FASTPATH_PREFETCH
+
 /* JEMALLOC_PROF enables allocation profiling. */
 #undef JEMALLOC_PROF
 
diff --git a/include/jemalloc/internal/jemalloc_internal_inlines_c.h b/include/jemalloc/internal/jemalloc_internal_inlines_c.h
index 2c61f8c4..16f86ad4 100644
--- a/include/jemalloc/internal/jemalloc_internal_inlines_c.h
+++ b/include/jemalloc/internal/jemalloc_internal_inlines_c.h
@@ -374,6 +374,12 @@ imalloc_fastpath(size_t size, void *(fallback_alloc)(size_t)) {
 	 */
 	ret = cache_bin_alloc_easy(bin, &tcache_success);
 	if (tcache_success) {
+#if defined(JEMALLOC_EXPERIMENTAL_FASTPATH_PREFETCH)
+		cache_bin_sz_t lb = (cache_bin_sz_t)(uintptr_t)bin->stack_head;
+		if(likely(lb != bin->low_bits_empty)) {
+			util_prefetch_write_range(*(bin->stack_head), usize);
+		}
+#endif
 		fastpath_success_finish(tsd, allocated_after, bin, ret);
 		return ret;
 	}