Added support to MEM_ROOT for write protected memory

This is useful for thing like Item_true and Item_false that we
allocated and initalize once and want to ensure that nothing can
change them

Main changes:
- Memory protection is achived by allocating memory with mmap() and
  protect it from write with mprotect()
- init_alloc_root(...,MY_ROOT_USE_MPROTECT) will create a
  memroot that one can later use with protect_root() to turn it
  read only or turn it back to read-write. All allocations to this
  memroot is done with mmap() to ensure page alligned allocations.
- alloc_root() code was rearranged to combine normal and valgrind code.
- init_alloc_root() now changes block size to be power of 2's, to get less
  memory fragmentation.
- Changed MEM_ROOT structure to make it smaller. Also renamed
  MEM_ROOT m_psi_key to psi_key.
- Moved MY_THREAD_SPECIFIC marker in MEM_ROOT from block size (old hack)
  to flags.
- Added global variable my_system_page_size. This is initialized at
  startup.

1 files changed, 1 insertions, 0 deletions

diff --git a/configure.cmake b/configure.cmake
index 03bb6b044fe..5d2ba365d65 100644
--- a/configure.cmake
+++ b/configure.cmake
@@ -374,6 +374,7 @@ CHECK_FUNCTION_EXISTS (mlock HAVE_MLOCK)
 CHECK_FUNCTION_EXISTS (mlockall HAVE_MLOCKALL)
 CHECK_FUNCTION_EXISTS (mmap HAVE_MMAP)
 CHECK_FUNCTION_EXISTS (mmap64 HAVE_MMAP64)
+CHECK_FUNCTION_EXISTS (mprotect HAVE_MPROTECT)
 CHECK_FUNCTION_EXISTS (perror HAVE_PERROR)
 CHECK_FUNCTION_EXISTS (poll HAVE_POLL)
 CHECK_FUNCTION_EXISTS (posix_fallocate HAVE_POSIX_FALLOCATE)