Bug#34043: Server loops excessively in _checkchunk() when safemalloc is enabled

Essentially, the problem is that safemalloc is excruciatingly
slow as it checks all allocated blocks for overrun at each
memory management primitive, yielding a almost exponential
slowdown for the memory management functions (malloc, realloc,
free). The overrun check basically consists of verifying some
bytes of a block for certain magic keys, which catches some
simple forms of overrun. Another minor problem is violation
of aliasing rules and that its own internal list of blocks
is prone to corruption.

Another issue with safemalloc is rather the maintenance cost
as the tool has a significant impact on the server code.
Given the magnitude of memory debuggers available nowadays,
especially those that are provided with the platform malloc
implementation, maintenance of a in-house and largely obsolete
memory debugger becomes a burden that is not worth the effort
due to its slowness and lack of support for detecting more
common forms of heap corruption.

Since there are third-party tools that can provide the same
functionality at a lower or comparable performance cost, the
solution is to simply remove safemalloc. Third-party tools
can provide the same functionality at a lower or comparable
performance cost. 

The removal of safemalloc also allows a simplification of the
malloc wrappers, removing quite a bit of kludge: redefinition
of my_malloc, my_free and the removal of the unused second
argument of my_free. Since free() always check whether the
supplied pointer is null, redudant checks are also removed.

Also, this patch adds unit testing for my_malloc and moves
my_realloc implementation into the same file as the other
memory allocation primitives.

client/mysqldump.c:
  Pass my_free directly as its signature is compatible with the
  callback type -- which wasn't the case for free_table_ent.

1 files changed, 5 insertions, 6 deletions

diff --git a/mysys/my_largepage.c b/mysys/my_largepage.c
index e65d3a0a5f5..9f5ab01a2b7 100644
--- a/mysys/my_largepage.c
+++ b/mysys/my_largepage.c
@@ -27,7 +27,7 @@
 
 static uint my_get_large_page_size_int(void);
 static uchar* my_large_malloc_int(size_t size, myf my_flags);
-static my_bool my_large_free_int(uchar* ptr, myf my_flags);
+static my_bool my_large_free_int(uchar* ptr);
 
 /* Gets the size of large pages from the OS */
 
@@ -70,7 +70,7 @@ uchar* my_large_malloc(size_t size, myf my_flags)
   to my_free_lock() in case of failure
  */
 
-void my_large_free(uchar* ptr, myf my_flags __attribute__((unused)))
+void my_large_free(uchar* ptr)
 {
   DBUG_ENTER("my_large_free");
   
@@ -79,9 +79,8 @@ void my_large_free(uchar* ptr, myf my_flags __attribute__((unused)))
     my_large_malloc_int(), i.e. my_malloc_lock() was used so we should free it
     with my_free_lock()
   */
-  if (!my_use_large_pages || !my_large_page_size ||
-      !my_large_free_int(ptr, my_flags))
-    my_free_lock(ptr, my_flags);
+  if (!my_use_large_pages || !my_large_page_size || !my_large_free_int(ptr))
+    my_free_lock(ptr);
 
   DBUG_VOID_RETURN;
 }
@@ -157,7 +156,7 @@ uchar* my_large_malloc_int(size_t size, myf my_flags)
 
 /* Linux-specific large pages deallocator */
 
-my_bool my_large_free_int(uchar *ptr, myf my_flags __attribute__((unused)))
+my_bool my_large_free_int(uchar *ptr)
 {
   DBUG_ENTER("my_large_free_int");
   DBUG_RETURN(shmdt(ptr) == 0);