Size of Huge Objects directly allocated to Old Generation

The maximum size of an object HotSpot JVM may allocate in young generation is nearly as large as the size of Eden (YoungGen minus two Survivor spaces).

That's how the allocation rougly looks like:

1. Use Thread Local Allocation Buffer (TLAB), if tlab_top + size <= tlab_end
   This is the fastest path. Allocation is just the tlab_top pointer increment.
2. If TLAB is almost full, create a new TLAB in Eden and retry in a fresh TLAB.
3. If TLAB remaining space is not enough but is still to big to discard, try to allocate an object directly in Eden. Allocation in Eden is also a pointer increment (eden_top + size <= eden_end) using atomic operation, since Eden is shared between all threads.
4. If allocation in Eden fails, a minor collection typically occurs.
5. If there is not enough space in Eden even after Young GC, an attempt to allocate directly in Old generation is made.

You can set the limit by using following flag

XX:PretenureSizeThreshold=size

its default value is 0 I assume that by default if you don't set it it doesn't get considered with value=0, that means by default there is no maximum value that acts as threshold, by default object gets promoted only based on number of GC survival

HotSpot version

java version "1.7.0_45"
Java(TM) SE Runtime Environment (build 1.7.0_45-b18)
Java HotSpot(TM) 64-Bit Server VM (build 24.45-b08, mixed mode)

to get all vm options (supported) you can run

java -XX:+PrintVMOptions -XX:+AggressiveOpts -XX:+UnlockDiagnosticVMOptions -XX:+UnlockExperimentalVMOptions -XX:+PrintFlagsFinal  -version

and then you can refer to hotspot vm option document or google particular option if not listed

byte[] array = new byte[300*1024*1024];

for(MemoryPoolMXBean memoryPoolMXBean: ManagementFactory.getMemoryPoolMXBeans()){
    System.out.println(memoryPoolMXBean.getName());
    System.out.println(memoryPoolMXBean.getUsage().getUsed());
}

outputs:

$ java -Xmx1500m -Xms1500m -Xmn500m -XX:PretenureSizeThreshold=100000000 -XX:+PrintGCDetails JVMMemoryInspection
Code Cache
393664
PS Eden Space
330301752
PS Survivor Space
0
PS Old Gen
0
PS Perm Gen
2749520