malloc: Add madvise support for Transparent Huge Pages

Linux Transparent Huge Pages (THP) current supports three different
states: 'never', 'madvise', and 'always'.  The 'never' is
self-explanatory and 'always' will enable THP for all anonymous
pages.  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.hugetlb',
where setting to a value diffent than 0 enables the madvise call.

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" and on Linux only support
one page size for THP, even if the architecture supports multiple
sizes.

To test is a new rule is added tests-malloc-hugetlb1, which run the
addes tests with the required GLIBC_TUNABLE setting.

Checked on x86_64-linux-gnu.

Reviewed-by: DJ Delorie <dj@redhat.com>

NEWS

@@ -92,6 +92,11 @@ Major new features:
   --enable-static-pie, which no longer has any effect on the build
   configuration.
 
+* On Linux, a new tunable, glibc.malloc.hugetlb, can be used to
+  make malloc issue madvise plus MADV_HUGEPAGE on mmap and sbrk calls.
+  Setting this might improve performance with Transparent Huge Pages madvise
+  mode depending of the workload.
+
 Deprecated and removed features, and other changes affecting compatibility:
 
 * On x86-64, the LD_PREFER_MAP_32BIT_EXEC environment variable support

Rules

@@ -157,6 +157,7 @@ tests: $(tests:%=$(objpfx)%.out) $(tests-internal:%=$(objpfx)%.out) \
        $(tests-container:%=$(objpfx)%.out) \
        $(tests-mcheck:%=$(objpfx)%-mcheck.out) \
        $(tests-malloc-check:%=$(objpfx)%-malloc-check.out) \
+       $(tests-malloc-hugetlb1:%=$(objpfx)%-malloc-hugetlb1.out) \
        $(tests-special) $(tests-printers-out)
 xtests: tests $(xtests:%=$(objpfx)%.out) $(xtests-special)
 endif
@@ -168,6 +169,7 @@ tests-expected =
 else
 tests-expected = $(tests) $(tests-internal) $(tests-printers) \
 	$(tests-container) $(tests-malloc-check:%=%-malloc-check) \
+	$(tests-malloc-hugetlb1:%=%-malloc-hugetlb1) \
 	$(tests-mcheck:%=%-mcheck)
 endif
 tests:
@@ -196,6 +198,7 @@ binaries-pie-notests =
 endif
 binaries-mcheck-tests = $(tests-mcheck:%=%-mcheck)
 binaries-malloc-check-tests = $(tests-malloc-check:%=%-malloc-check)
+binaries-malloc-hugetlb1-tests = $(tests-malloc-hugetlb1:%=%-malloc-hugetlb1)
 else
 binaries-all-notests =
 binaries-all-tests = $(tests) $(tests-internal) $(xtests) $(test-srcs)
@@ -207,6 +210,7 @@ binaries-pie-tests =
 binaries-pie-notests =
 binaries-mcheck-tests =
 binaries-malloc-check-tests =
+binaries-malloc-hugetlb1-tests =
 endif
 
 binaries-pie = $(binaries-pie-tests) $(binaries-pie-notests)
@@ -247,6 +251,14 @@ $(addprefix $(objpfx),$(binaries-malloc-check-tests)): %-malloc-check: %.o \
 	$(+link-tests)
 endif
 
+ifneq "$(strip $(binaries-malloc-hugetlb1-tests))" ""
+$(addprefix $(objpfx),$(binaries-malloc-hugetlb1-tests)): %-malloc-hugetlb1: %.o \
+  $(link-extra-libs-tests) \
+  $(sort $(filter $(common-objpfx)lib%,$(link-libc))) \
+  $(addprefix $(csu-objpfx),start.o) $(+preinit) $(+postinit)
+	$(+link-tests)
+endif
+
 ifneq "$(strip $(binaries-pie-tests))" ""
 $(addprefix $(objpfx),$(binaries-pie-tests)): %: %.o \
   $(link-extra-libs-tests) \
@@ -284,6 +296,13 @@ $(1)-malloc-check-ENV = MALLOC_CHECK_=3 \
 endef
 $(foreach t,$(tests-malloc-check),$(eval $(call malloc-check-ENVS,$(t))))
 
+# All malloc-hugetlb1 tests will be run with GLIBC_TUNABLES=glibc.malloc.hugetlb=1
+define malloc-hugetlb1-ENVS
+$(1)-malloc-hugetlb1-ENV += GLIBC_TUNABLES=glibc.malloc.hugetlb=1
+endef
+$(foreach t,$(tests-malloc-hugetlb1),$(eval $(call malloc-hugetlb1-ENVS,$(t))))
+
+
 # mcheck tests need the debug DSO to support -lmcheck.
 define mcheck-ENVS
 $(1)-mcheck-ENV = LD_PRELOAD=$(common-objpfx)/malloc/libc_malloc_debug.so

elf/dl-tunables.list

@@ -92,6 +92,11 @@ glibc {
       minval: 0
       security_level: SXID_IGNORE
     }
+    hugetlb {
+      type: INT_32
+      minval: 0
+      maxval: 1
+    }
   }
   cpu {
     hwcap_mask {

elf/tst-rtld-list-tunables.exp

@@ -1,6 +1,7 @@
 glibc.malloc.arena_max: 0x0 (min: 0x1, max: 0x[f]+)
 glibc.malloc.arena_test: 0x0 (min: 0x1, max: 0x[f]+)
 glibc.malloc.check: 0 (min: 0, max: 3)
+glibc.malloc.hugetlb: 0 (min: 0, max: 1)
 glibc.malloc.mmap_max: 0 (min: 0, max: 2147483647)
 glibc.malloc.mmap_threshold: 0x0 (min: 0x0, max: 0x[f]+)
 glibc.malloc.mxfast: 0x0 (min: 0x0, max: 0x[f]+)

malloc/Makefile

@@ -78,6 +78,22 @@ tests-exclude-malloc-check = tst-malloc-check tst-malloc-usable \
 tests-malloc-check = $(filter-out $(tests-exclude-malloc-check) \
 				  $(tests-static),$(tests))
 
+# Run all testes with GLIBC_TUNABLES=glibc.malloc.hugetlb=1 that check the
+# Transparent Huge Pages support.  We need exclude some tests that define
+# the ENV vars.
+tests-exclude-hugetlb1 = \
+	tst-compathooks-off \
+	tst-compathooks-on \
+	tst-interpose-nothread \
+	tst-interpose-thread \
+	tst-interpose-static-nothread \
+	tst-interpose-static-thread \
+	tst-malloc-usable \
+	tst-malloc-usable-tunables \
+	tst-mallocstate
+tests-malloc-hugetlb1 = \
+	$(filter-out $(tests-exclude-hugetlb1), $(tests))
+
 # -lmcheck needs __malloc_initialize_hook, which was deprecated in 2.24.
 ifeq ($(have-GLIBC_2.23)$(build-shared),yesyes)
 # Tests that don't play well with mcheck.  They are either bugs in mcheck or

malloc/arena.c

@@ -230,6 +230,7 @@ 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_hugetlb, int32_t)
 #else
 /* Initialization routine. */
 #include <string.h>
@@ -330,6 +331,7 @@ ptmalloc_init (void)
 	       TUNABLE_CALLBACK (set_tcache_unsorted_limit));
 # endif
   TUNABLE_GET (mxfast, size_t, TUNABLE_CALLBACK (set_mxfast));
+  TUNABLE_GET (hugetlb, int32_t, TUNABLE_CALLBACK (set_hugetlb));
 #else
   if (__glibc_likely (_environ != NULL))
     {
@@ -508,6 +510,9 @@ new_heap (size_t size, size_t top_pad)
       __munmap (p2, HEAP_MAX_SIZE);
       return 0;
     }
+
+  madvise_thp (p2, size);
+
   h = (heap_info *) p2;
   h->size = size;
   h->mprotect_size = size;

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;

malloc/malloc.c

@@ -1880,6 +1880,11 @@ 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;
@@ -2008,6 +2013,20 @@ free_perturb (char *p, size_t n)
 
 #include <stap-probe.h>
 
+/* ----------- Routines dealing with transparent huge pages ----------- */
+
+static inline void
+madvise_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"
 
@@ -2445,6 +2464,8 @@ sysmalloc (INTERNAL_SIZE_T nb, mstate av)
 
           if (mm != MAP_FAILED)
             {
+	      madvise_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
@@ -2606,6 +2627,8 @@ sysmalloc (INTERNAL_SIZE_T nb, mstate av)
       if (size > 0)
         {
           brk = (char *) (MORECORE (size));
+	  if (brk != (char *) (MORECORE_FAILURE))
+	    madvise_thp (brk, size);
           LIBC_PROBE (memory_sbrk_more, 2, brk, size);
         }
 
@@ -2637,6 +2660,8 @@ sysmalloc (INTERNAL_SIZE_T nb, mstate av)
 
               if (mbrk != MAP_FAILED)
                 {
+		  madvise_thp (mbrk, size);
+
                   /* We do not need, and cannot use, another sbrk call to find end */
                   brk = mbrk;
                   snd_brk = brk + size;
@@ -2748,6 +2773,8 @@ sysmalloc (INTERNAL_SIZE_T nb, mstate av)
                       correction = 0;
                       snd_brk = (char *) (MORECORE (0));
                     }
+		  else
+		    madvise_thp (snd_brk, correction);
                 }
 
               /* handle non-contiguous cases */
@@ -2988,6 +3015,8 @@ mremap_chunk (mchunkptr p, size_t new_size)
   if (cp == MAP_FAILED)
     return 0;
 
+  madvise_thp (cp, new_size);
+
   p = (mchunkptr) (cp + offset);
 
   assert (aligned_OK (chunk2mem (p)));
@@ -5316,6 +5345,24 @@ do_set_mxfast (size_t value)
   return 0;
 }
 
+#if HAVE_TUNABLES
+static __always_inline int
+do_set_hugetlb (int32_t value)
+{
+  if (value == 1)
+    {
+      enum malloc_thp_mode_t thp_mode = __malloc_thp_mode ();
+      /*
+	 Only enable THP madvise usage if system does support it and
+	 has 'madvise' mode.  Otherwise the madvise() call is wasteful.
+       */
+      if (thp_mode == malloc_thp_mode_madvise)
+	mp_.thp_pagesize = __malloc_default_thp_pagesize ();
+    }
+  return 0;
+}
+#endif
+
 int
 __libc_mallopt (int param_number, int value)
 {

manual/tunables.texi

@@ -270,6 +270,16 @@ 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.hugetlb
+This tunable controls the usage of Huge Pages on @code{malloc} calls.  The
+default value is @code{0}, which disables any additional support on
+@code{malloc}.
+
+Setting its value to @code{1} enables the use of @code{madvise} with
+@code{MADV_HUGEPAGE} after memory allocation with @code{mmap}.  It is enabled
+only if the system supports Transparent Huge Page (currently only on Linux).
+@end deftp
+
 @node Dynamic Linking Tunables
 @section Dynamic Linking Tunables
 @cindex dynamic linking tunables

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

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>
+
+unsigned long int
+__malloc_default_thp_pagesize (void)
+{
+  return 0;
+}
+
+enum malloc_thp_mode_t
+__malloc_thp_mode (void)
+{
+  return malloc_thp_mode_not_supported;
+}

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.  */
+unsigned long int __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 */

sysdeps/unix/sysv/linux/malloc-hugepages.c

@@ -0,0 +1,74 @@
+/* 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>
+
+unsigned long int
+__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 (unsigned long int)];
+  ssize_t s = __read_nocancel (fd, str, sizeof (str));
+  __close_nocancel (fd);
+  if (s < 0)
+    return 0;
+
+  unsigned long 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;
+}