From: Wilco Dijkstra <wilco.dijkstra@arm.com>
Date: Fri, 12 Dec 2025 11:58:28 +0000 (+0000)
Subject: malloc: Improve thp_init
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=1c588a2187a4f348ec155a1441784b51891bb667;p=thirdparty%2Fglibc.git

malloc: Improve thp_init

Cleanup thp_init, change it so that the DEFAULT_THP_PAGESIZE
setting can be overridden with glibc.malloc.hugetlb=0 tunable.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>
---

diff --git a/malloc/malloc.c b/malloc/malloc.c
index 08ca1879ac..be29929993 100644
--- a/malloc/malloc.c
+++ b/malloc/malloc.c
@@ -1902,25 +1902,29 @@ free_perturb (char *p, size_t n)
 
 /* ----------- Routines dealing with transparent huge pages ----------- */
 
-static void thp_init (void);
+static __always_inline void
+thp_init (void)
+{
+  /* Initialize only once if DEFAULT_THP_PAGESIZE is defined.  */
+  if (!DEFAULT_THP_PAGESIZE || mp_.thp_mode != malloc_thp_mode_not_supported)
+    return;
+
+  /* Set thp_pagesize even if thp_mode is never.  This reduces frequency
+     of MORECORE () invocation.  */
+  mp_.thp_mode = __malloc_thp_mode ();
+  mp_.thp_pagesize = DEFAULT_THP_PAGESIZE;
+}
 
 static inline void
 madvise_thp (void *p, INTERNAL_SIZE_T size)
 {
 #ifdef MADV_HUGEPAGE
 
-  /* Ensure thp_init () is invoked only once */
-  if (mp_.thp_pagesize < DEFAULT_THP_PAGESIZE)
-    thp_init ();
+  thp_init ();
 
-  /* Only use __madvise if the system is using 'madvise' mode.
-     Otherwise the call is wasteful. */
-  if (mp_.thp_mode != malloc_thp_mode_madvise)
-    return;
-
-  /* Do not consider areas smaller than a huge page or if the tunable is
-     not active.  */
-  if (mp_.thp_pagesize == 0 || size < mp_.thp_pagesize)
+  /* Only use __madvise if the system is using 'madvise' mode and the size
+     is at least a huge page, otherwise the call is wasteful. */
+  if (mp_.thp_mode != malloc_thp_mode_madvise || size < mp_.thp_pagesize)
     return;
 
   /* Linux requires the input address to be page-aligned, and unaligned
@@ -2468,9 +2472,8 @@ sysmalloc (INTERNAL_SIZE_T nb, mstate av)
          previous calls. Otherwise, we correct to page-align below.
        */
 
-      /* Ensure thp_init () is invoked only once */
-      if (mp_.thp_pagesize < DEFAULT_THP_PAGESIZE)
-        thp_init ();
+      /* Ensure thp_pagesize is initialized.  */
+      thp_init ();
 
       if (__glibc_unlikely (mp_.thp_pagesize != 0))
 	{
@@ -5126,7 +5129,9 @@ do_set_mxfast (size_t value)
 static __always_inline int
 do_set_hugetlb (size_t value)
 {
-  if (value == 1)
+  if (value == 0)
+    mp_.thp_mode = malloc_thp_mode_never;
+  else if (value == 1)
     {
       mp_.thp_mode = __malloc_thp_mode ();
       if (mp_.thp_mode == malloc_thp_mode_madvise
@@ -5139,15 +5144,6 @@ do_set_hugetlb (size_t value)
   return 0;
 }
 
-static __always_inline void
-thp_init (void)
-{
-  /* thp_pagesize is set even if thp_mode is never. This reduces frequency
-     of MORECORE () invocation.  */
-  mp_.thp_pagesize = DEFAULT_THP_PAGESIZE;
-  mp_.thp_mode = __malloc_thp_mode ();
-}
-
 int
 __libc_mallopt (int param_number, int value)
 {
diff --git a/sysdeps/unix/sysv/linux/aarch64/malloc-hugepages.h b/sysdeps/unix/sysv/linux/aarch64/malloc-hugepages.h
index f432ff7f0c..662f75cb78 100644
--- a/sysdeps/unix/sysv/linux/aarch64/malloc-hugepages.h
+++ b/sysdeps/unix/sysv/linux/aarch64/malloc-hugepages.h
@@ -16,6 +16,6 @@
    License along with the GNU C Library; see the file COPYING.LIB.  If
    not, see <https://www.gnu.org/licenses/>.  */
 
-# define DEFAULT_THP_PAGESIZE	1UL << 21
+#define DEFAULT_THP_PAGESIZE	(1UL << 21)
 
 #include_next <malloc-hugepages.h>