A DESCRIPTION OF THE REQUEST :
It would be very helpful to be able to ask how much memory has been allocated by a certain thread. For example, Thread could offer a (native) method:

  public long allocationTotal();

When a thread is new and has not run, this would be zero. As it runs, all allocations which occur within it would increment this number.

Rollover would be acceptable; only the difference between two readings, within a reasonably small amount of time, would be meaningful. (In some ways, it would be like the millisecond clock.)

JUSTIFICATION :
Often runaway or unintentional memory usage is hard to track down, especially if the objects created are short-lived. Allocation profiling helps but involves a lot of overhead, which often cannot be justified in the live systems where occasional, hard-to-reproduce memory overuse occurs.

I suspect this counter could be maintained very easily, with negligible overhead, and would allow meaningful paths of execution -- such as the servicing of a single web hit -- to be compared in their memory consumption. Those paths which 'stick out' (far above the norms for expected-similar operations) could be examined in more depth.

This feature could also supercede the RFE here -- http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6173675 ("M&M: approximate memory allocation rate per thread") -- as it would provide the raw numbers necessary to calculate various rates as desired. (Rate per time period, rate per request serviced, rate per database operation, etc.)

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
The following code would give meaningful info in the 'useDuring' variable:

long useBefore = Thread.currentThread().allocationTotal();
doSomething();
long useDuring = Thread.currentThread().allocationTotal() - useBefore;

ACTUAL -
No such method exists.