3 files changed, 142 insertions, 0 deletions

diff --git a/sysdeps/generic/malloc-hugepages.c b/sysdeps/generic/malloc-hugepages.c
index 8fb459a263..946284a33c 100644
--- a/sysdeps/generic/malloc-hugepages.c
+++ b/sysdeps/generic/malloc-hugepages.c
@@ -29,3 +29,11 @@ __malloc_thp_mode (void)
 {
   return malloc_thp_mode_not_supported;
 }
+
+/* Return the default transparent huge page size.  */
+void
+__malloc_hugepage_config (size_t requested, size_t *pagesize, int *flags)
+{
+  *pagesize = 0;
+  *flags = 0;
+}
diff --git a/sysdeps/generic/malloc-hugepages.h b/sysdeps/generic/malloc-hugepages.h
index f5a442e328..75cda3796a 100644
--- a/sysdeps/generic/malloc-hugepages.h
+++ b/sysdeps/generic/malloc-hugepages.h
@@ -34,4 +34,11 @@ enum malloc_thp_mode_t
 
 enum malloc_thp_mode_t __malloc_thp_mode (void) attribute_hidden;
 
+/* Return the supported huge page size from the REQUESTED sizes on PAGESIZE
+   along with the required extra mmap flags on FLAGS,  Requesting the value
+   of 0 returns the default huge page size, otherwise the value will be
+   matched against the sizes supported by the system.  */
+void __malloc_hugepage_config (size_t requested, size_t *pagesize, int *flags)
+     attribute_hidden;
+
 #endif /* _MALLOC_HUGEPAGES_H */
diff --git a/sysdeps/unix/sysv/linux/malloc-hugepages.c b/sysdeps/unix/sysv/linux/malloc-hugepages.c
index 7497e07260..0e05291d61 100644
--- a/sysdeps/unix/sysv/linux/malloc-hugepages.c
+++ b/sysdeps/unix/sysv/linux/malloc-hugepages.c
@@ -17,8 +17,10 @@
    not, see <https://www.gnu.org/licenses/>.  */
 
 #include <intprops.h>
+#include <dirent.h>
 #include <malloc-hugepages.h>
 #include <not-cancel.h>
+#include <sys/mman.h>
 
 unsigned long int
 __malloc_default_thp_pagesize (void)
@@ -72,3 +74,128 @@ __malloc_thp_mode (void)
     }
   return malloc_thp_mode_not_supported;
 }
+
+static size_t
+malloc_default_hugepage_size (void)
+{
+  int fd = __open64_nocancel ("/proc/meminfo", O_RDONLY);
+  if (fd == -1)
+    return 0;
+
+  size_t hpsize = 0;
+
+  char buf[512];
+  off64_t off = 0;
+  while (1)
+    {
+      ssize_t r = __pread64_nocancel (fd, buf, sizeof (buf) - 1, off);
+      if (r < 0)
+	break;
+      buf[r] = '\0';
+
+      /* If the tag is not found, read the last line again.  */
+      const char *s = strstr (buf, "Hugepagesize:");
+      if (s == NULL)
+	{
+	  char *nl = strrchr (buf, '\n');
+	  if (nl == NULL)
+	    break;
+	  off += (nl + 1) - buf;
+	  continue;
+	}
+
+      /* The default huge page size is in the form:
+	 Hugepagesize:       NUMBER kB  */
+      s += sizeof ("Hugepagesize: ") - 1;
+      for (int i = 0; (s[i] >= '0' && s[i] <= '9') || s[i] == ' '; i++)
+	{
+	  if (s[i] == ' ')
+	    continue;
+	  hpsize *= 10;
+	  hpsize += s[i] - '0';
+	}
+      hpsize *= 1024;
+      break;
+    }
+
+  __close_nocancel (fd);
+
+  return hpsize;
+}
+
+static inline int
+hugepage_flags (size_t pagesize)
+{
+  return MAP_HUGETLB | (__builtin_ctzll (pagesize) << MAP_HUGE_SHIFT);
+}
+
+void
+__malloc_hugepage_config (size_t requested, size_t *pagesize, int *flags)
+{
+  *pagesize = 0;
+  *flags = 0;
+
+  if (requested == 0)
+    {
+      *pagesize = malloc_default_hugepage_size ();
+      if (*pagesize != 0)
+	*flags = hugepage_flags (*pagesize);
+      return;
+    }
+
+  /* Each entry represents a supported huge page in the form of:
+     hugepages-<size>kB.  */
+  int dirfd = __open64_nocancel ("/sys/kernel/mm/hugepages",
+				 O_RDONLY | O_DIRECTORY, 0);
+  if (dirfd == -1)
+    return;
+
+  char buffer[1024];
+  while (true)
+    {
+#if !IS_IN(libc)
+# define __getdents64 getdents64
+#endif
+      ssize_t ret = __getdents64 (dirfd, buffer, sizeof (buffer));
+      if (ret == -1)
+	break;
+      else if (ret == 0)
+        break;
+
+      bool found = false;
+      char *begin = buffer, *end = buffer + ret;
+      while (begin != end)
+        {
+          unsigned short int d_reclen;
+          memcpy (&d_reclen, begin + offsetof (struct dirent64, d_reclen),
+                  sizeof (d_reclen));
+          const char *dname = begin + offsetof (struct dirent64, d_name);
+          begin += d_reclen;
+
+          if (dname[0] == '.'
+	      || strncmp (dname, "hugepages-", sizeof ("hugepages-") - 1) != 0)
+            continue;
+
+	  size_t hpsize = 0;
+	  const char *sizestr = dname + sizeof ("hugepages-") - 1;
+	  for (int i = 0; sizestr[i] >= '0' && sizestr[i] <= '9'; i++)
+	    {
+	      hpsize *= 10;
+	      hpsize += sizestr[i] - '0';
+	    }
+	  hpsize *= 1024;
+
+	  if (hpsize == requested)
+	    {
+	      *pagesize = hpsize;
+	      *flags = hugepage_flags (*pagesize);
+	      found = true;
+	      break;
+	    }
+        }
+      if (found)
+	break;
+    }
+
+  __close_nocancel (dirfd);
+}