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/config.h.cmake b/config.h.cmake
index 80721592ab0..44ae067daad 100644
--- a/config.h.cmake
+++ b/config.h.cmake
@@ -179,6 +179,7 @@
 #cmakedefine HAVE_MLOCKALL 1
 #cmakedefine HAVE_MMAP 1
 #cmakedefine HAVE_MMAP64 1
+#cmakedefine HAVE_MPROTECT 1
 #cmakedefine HAVE_PERROR 1
 #cmakedefine HAVE_POLL 1
 #cmakedefine HAVE_POSIX_FALLOCATE 1