[PATCH v2 1/4] malloc: Add madvise support for Transparent Huge Pages

[Adhemerval Zanella <adhemerval.zanella@linaro.org>]

Linux Transparent Huge Pages (THP) current support three different
states: 'never', 'madvise', and 'always'.  The 'never' is
self-explanatory and 'always' will enable THP for all anonymous
memory.  However, 'madvise' is still the default for some system and
for such case THP will be only used if the memory range is explicity
advertise by the program through a madvise(MADV_HUGEPAGE) call.

To enable it a new tunable is provided, 'glibc.malloc.thp_madvise',
where setting to a value diffent than 0 enables the madvise call.
Linux current only support one page size for THP, even if the
architecture supports multiple sizes.

This patch issues the madvise(MADV_HUGEPAGE) call after a successful
mmap() call at sysmalloc() with sizes larger than the default huge
page size.  The madvise() call is disable is system does not support
THP or if it has the mode set to "never".

Checked on x86_64-linux-gnu.
---
 NEWS                                       |  5 +-
 elf/dl-tunables.list                       |  5 ++
 elf/tst-rtld-list-tunables.exp             |  1 +
 malloc/arena.c                             |  5 ++
 malloc/malloc-internal.h                   |  1 +
 malloc/malloc.c                            | 48 ++++++++++++++
 manual/tunables.texi                       |  9 +++
 sysdeps/generic/Makefile                   |  8 +++
 sysdeps/generic/malloc-hugepages.c         | 31 +++++++++
 sysdeps/generic/malloc-hugepages.h         | 37 +++++++++++
 sysdeps/unix/sysv/linux/malloc-hugepages.c | 76 ++++++++++++++++++++++
 11 files changed, 225 insertions(+), 1 deletion(-)
 create mode 100644 sysdeps/generic/malloc-hugepages.c
 create mode 100644 sysdeps/generic/malloc-hugepages.h
 create mode 100644 sysdeps/unix/sysv/linux/malloc-hugepages.c

diff --git a/NEWS b/NEWS
index 79c895e382..9b2345d08c 100644
--- a/NEWS
+++ b/NEWS
@@ -9,7 +9,10 @@ Version 2.35
 
 Major new features:
 
-  [Add new features here]
+* On Linux, a new tunable, glibc.malloc.thp_madvise, can be used to
+  make malloc issue madvise plus MADV_HUGEPAGE on mmap and sbrk calls.
+  It might improve performance with Transparent Huge Pages madvise mode
+  depending of the workload.
 
 Deprecated and removed features, and other changes affecting compatibility:
 
diff --git a/elf/dl-tunables.list b/elf/dl-tunables.list
index 8ddd4a2314..67df6dbc2c 100644
--- a/elf/dl-tunables.list
+++ b/elf/dl-tunables.list
@@ -92,6 +92,11 @@ glibc {
       minval: 0
       security_level: SXID_IGNORE
     }
+    thp_madvise {
+      type: INT_32
+      minval: 0
+      maxval: 1
+    }
   }
   cpu {
     hwcap_mask {
diff --git a/elf/tst-rtld-list-tunables.exp b/elf/tst-rtld-list-tunables.exp
index 9f66c52885..d8109fa31c 100644
--- a/elf/tst-rtld-list-tunables.exp
+++ b/elf/tst-rtld-list-tunables.exp
@@ -8,6 +8,7 @@ glibc.malloc.perturb: 0 (min: 0, max: 255)
 glibc.malloc.tcache_count: 0x0 (min: 0x0, max: 0x[f]+)
 glibc.malloc.tcache_max: 0x0 (min: 0x0, max: 0x[f]+)
 glibc.malloc.tcache_unsorted_limit: 0x0 (min: 0x0, max: 0x[f]+)
+glibc.malloc.thp_madvise: 0 (min: 0, max: 1)
 glibc.malloc.top_pad: 0x0 (min: 0x0, max: 0x[f]+)
 glibc.malloc.trim_threshold: 0x0 (min: 0x0, max: 0x[f]+)
 glibc.rtld.nns: 0x4 (min: 0x1, max: 0x10)
diff --git a/malloc/arena.c b/malloc/arena.c
index 667484630e..81bff54303 100644
--- a/malloc/arena.c
+++ b/malloc/arena.c
@@ -231,6 +231,7 @@ TUNABLE_CALLBACK_FNDECL (set_tcache_count, size_t)
 TUNABLE_CALLBACK_FNDECL (set_tcache_unsorted_limit, size_t)
 #endif
 TUNABLE_CALLBACK_FNDECL (set_mxfast, size_t)
+TUNABLE_CALLBACK_FNDECL (set_thp_madvise, int32_t)
 #else
 /* Initialization routine. */
 #include <string.h>
@@ -331,6 +332,7 @@ ptmalloc_init (void)
 	       TUNABLE_CALLBACK (set_tcache_unsorted_limit));
 # endif
   TUNABLE_GET (mxfast, size_t, TUNABLE_CALLBACK (set_mxfast));
+  TUNABLE_GET (thp_madvise, int32_t, TUNABLE_CALLBACK (set_thp_madvise));
 #else
   if (__glibc_likely (_environ != NULL))
     {
@@ -509,6 +511,9 @@ new_heap (size_t size, size_t top_pad)
       __munmap (p2, HEAP_MAX_SIZE);
       return 0;
     }
+
+  sysmadvise_thp (p2, size);
+
   h = (heap_info *) p2;
   h->size = size;
   h->mprotect_size = size;
diff --git a/malloc/malloc-internal.h b/malloc/malloc-internal.h
index 0c7b5a183c..7493e34d86 100644
--- a/malloc/malloc-internal.h
+++ b/malloc/malloc-internal.h
@@ -22,6 +22,7 @@
 #include <malloc-machine.h>
 #include <malloc-sysdep.h>
 #include <malloc-size.h>
+#include <malloc-hugepages.h>
 
 /* Called in the parent process before a fork.  */
 void __malloc_fork_lock_parent (void) attribute_hidden;
diff --git a/malloc/malloc.c b/malloc/malloc.c
index e065785af7..ad3eec41ac 100644
--- a/malloc/malloc.c
+++ b/malloc/malloc.c
@@ -1881,6 +1881,11 @@ struct malloc_par
   INTERNAL_SIZE_T arena_test;
   INTERNAL_SIZE_T arena_max;
 
+#if HAVE_TUNABLES
+  /* Transparent Large Page support.  */
+  INTERNAL_SIZE_T thp_pagesize;
+#endif
+
   /* Memory map support */
   int n_mmaps;
   int n_mmaps_max;
@@ -2009,6 +2014,20 @@ free_perturb (char *p, size_t n)
 
 #include <stap-probe.h>
 
+/* ----------- Routines dealing with transparent huge pages ----------- */
+
+static inline void
+sysmadvise_thp (void *p, INTERNAL_SIZE_T size)
+{
+#if HAVE_TUNABLES && defined (MADV_HUGEPAGE)
+  /* 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)
+    return;
+  __madvise (p, size, MADV_HUGEPAGE);
+#endif
+}
+
 /* ------------------- Support for multiple arenas -------------------- */
 #include "arena.c"
 
@@ -2446,6 +2465,8 @@ sysmalloc (INTERNAL_SIZE_T nb, mstate av)
 
           if (mm != MAP_FAILED)
             {
+	      sysmadvise_thp (mm, size);
+
               /*
                  The offset to the start of the mmapped region is stored
                  in the prev_size field of the chunk. This allows us to adjust
@@ -2607,6 +2628,8 @@ sysmalloc (INTERNAL_SIZE_T nb, mstate av)
       if (size > 0)
         {
           brk = (char *) (MORECORE (size));
+	  if (brk != (char *) (MORECORE_FAILURE))
+	    sysmadvise_thp (brk, size);
           LIBC_PROBE (memory_sbrk_more, 2, brk, size);
         }
 
@@ -2638,6 +2661,8 @@ sysmalloc (INTERNAL_SIZE_T nb, mstate av)
 
               if (mbrk != MAP_FAILED)
                 {
+		  sysmadvise_thp (mbrk, size);
+
                   /* We do not need, and cannot use, another sbrk call to find end */
                   brk = mbrk;
                   snd_brk = brk + size;
@@ -2749,6 +2774,8 @@ sysmalloc (INTERNAL_SIZE_T nb, mstate av)
                       correction = 0;
                       snd_brk = (char *) (MORECORE (0));
                     }
+		  else
+		    sysmadvise_thp (snd_brk, correction);
                 }
 
               /* handle non-contiguous cases */
@@ -2989,6 +3016,8 @@ mremap_chunk (mchunkptr p, size_t new_size)
   if (cp == MAP_FAILED)
     return 0;
 
+  sysmadvise_thp (cp, new_size);
+
   p = (mchunkptr) (cp + offset);
 
   assert (aligned_OK (chunk2mem (p)));
@@ -5325,6 +5354,25 @@ do_set_mxfast (size_t value)
   return 0;
 }
 
+#if HAVE_TUNABLES
+static __always_inline int
+do_set_thp_madvise (int32_t value)
+{
+  if (value > 0)
+    {
+      enum malloc_thp_mode_t thp_mode = __malloc_thp_mode ();
+      /*
+	 Only enables THP usage is system does support it and has at least
+	 always or madvise mode.  Otherwise the madvise() call is wasteful.
+       */
+      if (thp_mode != malloc_thp_mode_not_supported
+	  && thp_mode != malloc_thp_mode_never)
+	mp_.thp_pagesize = __malloc_default_thp_pagesize ();
+    }
+  return 0;
+}
+#endif
+
 int
 __libc_mallopt (int param_number, int value)
 {
diff --git a/manual/tunables.texi b/manual/tunables.texi
index 658547c613..93c46807f9 100644
--- a/manual/tunables.texi
+++ b/manual/tunables.texi
@@ -270,6 +270,15 @@ pointer, so add 4 on 32-bit systems or 8 on 64-bit systems to the size
 passed to @code{malloc} for the largest bin size to enable.
 @end deftp
 
+@deftp Tunable glibc.malloc.thp_madivse
+This tunable enable the use of @code{madvise} with @code{MADV_HUGEPAGE} after
+the system allocator allocated memory through @code{mmap} if the system supports
+Transparent Huge Page (currently only Linux).
+
+The default value of this tunable is @code{0}, which disable its usage.
+Setting to a positive value enable the @code{madvise} call.
+@end deftp
+
 @node Dynamic Linking Tunables
 @section Dynamic Linking Tunables
 @cindex dynamic linking tunables
diff --git a/sysdeps/generic/Makefile b/sysdeps/generic/Makefile
index a209e85cc4..8eef83c94d 100644
--- a/sysdeps/generic/Makefile
+++ b/sysdeps/generic/Makefile
@@ -27,3 +27,11 @@ sysdep_routines += framestate unwind-pe
 shared-only-routines += framestate unwind-pe
 endif
 endif
+
+ifeq ($(subdir),malloc)
+sysdep_malloc_debug_routines += malloc-hugepages
+endif
+
+ifeq ($(subdir),misc)
+sysdep_routines += malloc-hugepages
+endif
diff --git a/sysdeps/generic/malloc-hugepages.c b/sysdeps/generic/malloc-hugepages.c
new file mode 100644
index 0000000000..262bcdbeb8
--- /dev/null
+++ b/sysdeps/generic/malloc-hugepages.c
@@ -0,0 +1,31 @@
+/* Huge Page support.  Generic implementation.
+   Copyright (C) 2021 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public License as
+   published by the Free Software Foundation; either version 2.1 of the
+   License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; see the file COPYING.LIB.  If
+   not, see <https://www.gnu.org/licenses/>.  */
+
+#include <malloc-hugepages.h>
+
+size_t
+__malloc_default_thp_pagesize (void)
+{
+  return 0;
+}
+
+enum malloc_thp_mode_t
+__malloc_thp_mode (void)
+{
+  return malloc_thp_mode_not_supported;
+}
diff --git a/sysdeps/generic/malloc-hugepages.h b/sysdeps/generic/malloc-hugepages.h
new file mode 100644
index 0000000000..664cda9b67
--- /dev/null
+++ b/sysdeps/generic/malloc-hugepages.h
@@ -0,0 +1,37 @@
+/* Malloc huge page support.  Generic implementation.
+   Copyright (C) 2021 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public License as
+   published by the Free Software Foundation; either version 2.1 of the
+   License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; see the file COPYING.LIB.  If
+   not, see <https://www.gnu.org/licenses/>.  */
+
+#ifndef _MALLOC_HUGEPAGES_H
+#define _MALLOC_HUGEPAGES_H
+
+#include <stddef.h>
+
+/* Return the default transparent huge page size.  */
+size_t __malloc_default_thp_pagesize (void) attribute_hidden;
+
+enum malloc_thp_mode_t
+{
+  malloc_thp_mode_always,
+  malloc_thp_mode_madvise,
+  malloc_thp_mode_never,
+  malloc_thp_mode_not_supported
+};
+
+enum malloc_thp_mode_t __malloc_thp_mode (void) attribute_hidden;
+
+#endif /* _MALLOC_HUGEPAGES_H */
diff --git a/sysdeps/unix/sysv/linux/malloc-hugepages.c b/sysdeps/unix/sysv/linux/malloc-hugepages.c
new file mode 100644
index 0000000000..66589127cd
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/malloc-hugepages.c
@@ -0,0 +1,76 @@
+/* Huge Page support.  Linux implementation.
+   Copyright (C) 2021 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public License as
+   published by the Free Software Foundation; either version 2.1 of the
+   License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; see the file COPYING.LIB.  If
+   not, see <https://www.gnu.org/licenses/>.  */
+
+#include <intprops.h>
+#include <malloc-hugepages.h>
+#include <not-cancel.h>
+
+size_t
+__malloc_default_thp_pagesize (void)
+{
+  int fd = __open64_nocancel (
+    "/sys/kernel/mm/transparent_hugepage/hpage_pmd_size", O_RDONLY);
+  if (fd == -1)
+    return 0;
+
+
+  char str[INT_BUFSIZE_BOUND (size_t)];
+  ssize_t s = __read_nocancel (fd, str, sizeof (str));
+  __close_nocancel (fd);
+
+  if (s < 0)
+    return 0;
+
+  int r = 0;
+  for (ssize_t i = 0; i < s; i++)
+    {
+      if (str[i] == '\n')
+	break;
+      r *= 10;
+      r += str[i] - '0';
+    }
+  return r;
+}
+
+enum malloc_thp_mode_t
+__malloc_thp_mode (void)
+{
+  int fd = __open64_nocancel ("/sys/kernel/mm/transparent_hugepage/enabled",
+			      O_RDONLY);
+  if (fd == -1)
+    return malloc_thp_mode_not_supported;
+
+  static const char mode_always[]  = "[always] madvise never\n";
+  static const char mode_madvise[] = "always [madvise] never\n";
+  static const char mode_never[]   = "always madvise [never]\n";
+
+  char str[sizeof(mode_always)];
+  ssize_t s = __read_nocancel (fd, str, sizeof (str));
+  __close_nocancel (fd);
+
+  if (s == sizeof (mode_always) - 1)
+    {
+      if (strcmp (str, mode_always) == 0)
+	return malloc_thp_mode_always;
+      else if (strcmp (str, mode_madvise) == 0)
+	return malloc_thp_mode_madvise;
+      else if (strcmp (str, mode_never) == 0)
+	return malloc_thp_mode_never;
+    }
+  return malloc_thp_mode_not_supported;
+}
-- 
2.30.2