[PATCH 2/3] malloc: Add THP/madvise support for sbrk

[Adhemerval Zanella via Libc-alpha <libc-alpha@sourceware.org>]

For the main arena, the sbrk() might the preferable syscall instead of
mmap().  And the granularity used when increasing the program segment
is the default page size.

To increase effectiveness with Transparent Huge Page with madvise, the
large page size is use instead.  This is enabled with the new tunable
'glibc.malloc.thp_pagesize'.

Checked on x86_64-linux-gnu.
---
 malloc/malloc.c | 40 +++++++++++++++++++++++++++++++++++-----
 1 file changed, 35 insertions(+), 5 deletions(-)

diff --git a/malloc/malloc.c b/malloc/malloc.c
index 52ea84a63d..7cd586c866 100644
--- a/malloc/malloc.c
+++ b/malloc/malloc.c
@@ -2028,6 +2028,38 @@ sysmadvise_thp (void *p, INTERNAL_SIZE_T size)
 #endif
 }
 
+static inline long int
+thp_brk_align_up (long int size)
+{
+  INTERNAL_SIZE_T r = size;
+#if HAVE_TUNABLES && defined (MADV_HUGEPAGE)
+  /* Defined in brk.c.  */
+  extern void *__curbrk;
+  if (mp_.thp_pagesize != 0)
+    {
+      uintptr_t top = ALIGN_UP ((uintptr_t)__curbrk + size, mp_.thp_pagesize);
+      r = top - (uintptr_t)__curbrk;
+    }
+  else
+#endif
+    r = ALIGN_UP (size, GLRO(dl_pagesize));
+  return r;
+}
+
+static inline long
+thp_brk_align_down (long int top)
+{
+  long r;
+#if HAVE_TUNABLES && defined (MADV_HUGEPAGE)
+  if (mp_.thp_pagesize != 0)
+    r = ALIGN_DOWN (top, mp_.thp_pagesize);
+  else
+#endif
+    r = ALIGN_DOWN (top, GLRO(dl_pagesize));
+  return r;
+}
+
+
 /* ------------------- Support for multiple arenas -------------------- */
 #include "arena.c"
 
@@ -2610,14 +2642,14 @@ sysmalloc (INTERNAL_SIZE_T nb, mstate av)
         size -= old_size;
 
       /*
-         Round to a multiple of page size.
+         Round to a multiple of page size or huge page size.
          If MORECORE is not contiguous, this ensures that we only call it
          with whole-page arguments.  And if MORECORE is contiguous and
          this is not first time through, this preserves page-alignment of
          previous calls. Otherwise, we correct to page-align below.
        */
 
-      size = ALIGN_UP (size, pagesize);
+      size = thp_brk_align_up (size);
 
       /*
          Don't try to call MORECORE if argument is so big as to appear
@@ -2900,10 +2932,8 @@ systrim (size_t pad, mstate av)
   long released;         /* Amount actually released */
   char *current_brk;     /* address returned by pre-check sbrk call */
   char *new_brk;         /* address returned by post-check sbrk call */
-  size_t pagesize;
   long top_area;
 
-  pagesize = GLRO (dl_pagesize);
   top_size = chunksize (av->top);
 
   top_area = top_size - MINSIZE - 1;
@@ -2911,7 +2941,7 @@ systrim (size_t pad, mstate av)
     return 0;
 
   /* Release in pagesize units and round down to the nearest page.  */
-  extra = ALIGN_DOWN(top_area - pad, pagesize);
+  extra = thp_brk_align_down (top_area - pad);
 
   if (extra == 0)
     return 0;
-- 
2.30.2