Make IO_SIZE compile-time configurable

Making mariadb's IO_SIZE compile-time configurable enables more
straight-forward investigation of the performance implications of having
an IO_SIZE which is different than the memory page size.

The default IO_SIZE of 4096 as defined in include/my_global.h matches
the memory page size of most systems. Larger page sizes are widely
supported, called "huge pages" in Linux, "superpages" in FreeBSD, and
"large pages" in MS Windows.

On POSIX systems, obtaining the page size can be done via:

	page_size= sysconf(_SC_PAGESIZE);

On Windows:

	SYSTEM_INFO si;
	GetSystemInfo(&si);
	page_size= si.dwPageSize;

In https://jira.mariadb.org/browse/MDEV-35740 Marko highlights that
there are vastly different uses of IO_SIZE. This "one size fits all"
nature of IO_SIZE is not ideal, future work could split this into
separate constants based upon usage.

See also:
mariadb-corporation/mariadb-connector-c#267

Signed-off-by: Eric Herman <[email protected]>

Author: ericherman

CMakeLists.txt

@@ -191,6 +191,15 @@ ELSE()
   SET (SKIP_COMPONENTS "N-O-N-E")
 ENDIF()
 
+# I/O buffer size. May be smaller than the disk page size.
+# 4096 is a common block size on SSDs.
+# This influences the speed of the isam btree library.
+# E.g.: too big may become too slow.
+SET(IO_SIZE 4096 CACHE STRING "Specify the I/O buffer size")
+math(EXPR is_power_of_two "(${IO_SIZE} & (${IO_SIZE} - 1))")
+IF(IO_SIZE LESS 512 OR NOT is_power_of_two EQUAL 0)
+  message(FATAL_ERROR "IO_SIZE ${IO_SIZE} must >= 512 and a power of 2.")
+ENDIF()
 
 SET(MEMPROTECT_DEFAULT ON)
 

config.h.cmake

@@ -551,3 +551,5 @@ this is the case with Microsoft Windows VirtualFree(MEM_DECOMMIT) */
 #endif
 
 #cmakedefine HAVE_VFORK 1
+
+#cmakedefine IO_SIZE @IO_SIZE@

include/my_global.h

@@ -664,17 +664,6 @@ typedef SOCKET_SIZE_TYPE size_socket;
 #define OS_FILE_LIMIT	UINT_MAX
 #endif
 
-/*
-  I/O buffer size. May be smaller than the disk page size.
-  This influences the speed of the isam btree library.
-  E.g.: too big may become too slow.
-  4096 is a common block size on SSDs.
-*/
-#define IO_SIZE			4096U
-#if (IO_SIZE < 512) || (IO_SIZE & (IO_SIZE-1))
-#error "IO_SIZE must be a positive multiple of 512 and power of 2"
-#endif
-
 /*
   How much overhead does malloc/my_malloc have. The code often allocates
   something like 1024-MALLOC_OVERHEAD bytes