[PATCH] malloc: Show hugetlb tunable default in --list-tunables

[Wilco Dijkstra]

Explicitly set the hugetlb tunable value in aarch64/cpu-features.c so it
is shown as 1 with /lib/ld-linux-aarch64.so.1 --list-tunables.
Move the intitialization of thp_mode/thp_pagesize to do_set_hugetlb() and
avoid accessing /sys/kernel/mm if DEFAULT_THP_PAGESIZE > 0.

Passes regress, OK for commit?

---

diff --git a/malloc/arena.c b/malloc/arena.c
index 75f2f32b5f61a33a06dc285ca9899a708c78cf10..d2ed6279226856d630cfdf734303c4b936512f58 100644
--- a/malloc/arena.c
+++ b/malloc/arena.c
@@ -275,15 +275,6 @@ __ptmalloc_init (void)
     __always_fail_morecore = true;
 #endif
 
-  /* Enable THP if DEFAULT_THP_PAGESIZE is non-zero.  Avoid quering the THP
-     page size or mode since accessing /sys/kernel/mm is relatively slow and
-     might not be accessible in containers.  */
-  if (DEFAULT_THP_PAGESIZE > 0)
-    {
-      mp_.thp_mode = malloc_thp_mode_madvise;
-      mp_.thp_pagesize = DEFAULT_THP_PAGESIZE;
-    }
-
   thread_arena = &main_arena;
 
   malloc_init_state (&main_arena);
diff --git a/malloc/malloc.c b/malloc/malloc.c
index 4aac196533d896353e3a32e34fa143d03eb82627..7241a79a936999ab5c3ac989133ad4c7919eec31 100644
--- a/malloc/malloc.c
+++ b/malloc/malloc.c
@@ -5026,13 +5026,25 @@ do_set_mxfast (size_t value)
 static __always_inline int
 do_set_hugetlb (size_t value)
 {
+  /* Enable THP if DEFAULT_THP_PAGESIZE is non-zero.  */
+  if (DEFAULT_THP_PAGESIZE > 0)
+    {
+      mp_.thp_mode = malloc_thp_mode_madvise;
+      mp_.thp_pagesize = DEFAULT_THP_PAGESIZE;
+    }
+
   if (value == 0)
     mp_.thp_mode = malloc_thp_mode_never;
   else if (value == 1)
     {
+      /* Avoid querying the THP page size/mode since accessing /sys/kernel/mm
+	 is relatively slow and might not be accessible in containers.  */
+      if (DEFAULT_THP_PAGESIZE > 0)
+	return 0;
+
       mp_.thp_mode = __malloc_thp_mode ();
       if (mp_.thp_mode == malloc_thp_mode_madvise
-          || mp_.thp_mode == malloc_thp_mode_always)
+	  || mp_.thp_mode == malloc_thp_mode_always)
 	mp_.thp_pagesize = __malloc_default_thp_pagesize ();
     }
   else if (value >= 2)
diff --git a/sysdeps/unix/sysv/linux/aarch64/cpu-features.c b/sysdeps/unix/sysv/linux/aarch64/cpu-features.c
index 70d3272772f5f36a3435d0ae8919d781a1e2412e..af502eff82e05efbe0a2e9418a71473e5c7ec8b9 100644
--- a/sysdeps/unix/sysv/linux/aarch64/cpu-features.c
+++ b/sysdeps/unix/sysv/linux/aarch64/cpu-features.c
@@ -179,4 +179,8 @@ init_cpu_features (struct cpu_features *cpu_features)
   if (GLRO (dl_hwcap) & HWCAP_GCS)
     /* GCS status may be updated later by binary compatibility checks.  */
     GL (dl_aarch64_gcs) = TUNABLE_GET (glibc, cpu, aarch64_gcs, uint64_t, 0);
+
+  /* Default to glibc.malloc.hugetlb=1 if the tunable is not set.  */
+  if (!TUNABLE_IS_INITIALIZED (glibc, malloc, hugetlb))
+    TUNABLE_SET (glibc, malloc, hugetlb, 1);
 }