Reduce number of mmap calls from __libc_memalign in ld.so

__libc_memalign in ld.so allocates one page at a time and tries to
optimize consecutive __libc_memalign calls by hoping that the next
mmap is after the current memory allocation.

However, the kernel hands out mmap addresses in top-down order, so
this optimization in practice never happens, with the result that we
have more mmap calls and waste a bunch of space for each __libc_memalign.

This change makes __libc_memalign to mmap one page extra.  Worst case,
the kernel never puts a backing page behind it, but best case it allows
__libc_memalign to operate much much better.  For elf/tst-align --direct,
it reduces number of mmap calls from 12 to 9.

	* elf/dl-minimal.c (__libc_memalign): Mmap one extra page.

1 files changed, 4 insertions, 0 deletions

diff --git a/ChangeLog b/ChangeLog
index 5cd8c4012b..744c0c0fb7 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+2016-04-23   H.J. Lu  <hongjiu.lu@intel.com>
+
+	* elf/dl-minimal.c (__libc_memalign): Mmap one extra page.
+
 2016-04-23  Mike Frysinger  <vapier@gentoo.org>
 
 	* locale/programs/ld-time.c (time_finish): Set week_1stweek to 7