How do I allocate an NSObject onto its own virtual memory page in iOS?

Question

I want to allocate an NSObject onto its own virtual memory page. Is this possible? It seems trivial if we could still use NSZones, but they are deprecated. I tried using NSZoneFromPointer, but it always returned nil. According to Tips for Allocating Memory:

For large memory allocations, where large is anything more than a few virtual memory pages, malloc automatically uses the vm_allocate routine to obtain the requested memory.

Thus, it seems like I should be able to just make my object as large as a few pages thusly:

@interface MyObject : NSObject {
int[40960]; // 4096 is the default page size, so this is 10 pages.
}

@implementation MyObject
@end

I realize this is a hack, but would it work consistently? Is there a better way?

Answer 1

From twitter:

objc_constructInstance(…) might let you do what you want...

From <objc/runtime.h>:

/** 
 * Creates an instance of a class at the specific location provided.
 * 
 * @param cls The class that you wish to allocate an instance of.
 * @param bytes The location at which to allocate an instance of \e cls.
 *  Must point to at least \c class_getInstanceSize(cls) bytes of well-aligned,
 *  zero-filled memory.
 *
 * @return \e bytes on success, \c nil otherwise. (For example, \e cls or \e bytes
 *  might be \c nil)
 *
 * @see class_createInstance
 */
OBJC_EXPORT id objc_constructInstance(Class cls, void *bytes) 
    __OSX_AVAILABLE_STARTING(__MAC_10_6, __IPHONE_3_0)
    OBJC_ARC_UNAVAILABLE;

It looks like objc_constructInstance is the answer.

Answer 2

I don't think as a user-level application you are supposed to have any control over virtual memory assignments. Apps in iOS are in a sandbox.