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>

1 files changed, 74 insertions, 0 deletions

diff --git a/sysdeps/unix/sysv/linux/malloc-hugepages.c b/sysdeps/unix/sysv/linux/malloc-hugepages.c
new file mode 100644
index 0000000000..7497e07260
--- /dev/null
+++ b/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;
+}