MySQL InnoDB memory performance tuning

Hi, I have a fairly small (data dir is 1.2GB) InnoDB database managed
by MySQL 5.4.3-beta on an 8-core x86_64 Linux box with 16GB RAM. I'd
like to use as much of the memory as possible, but despite specifying
(e.g.) --innodb-buffer-pool-size=3000000000, mysql only ever takes up
374M of resident memory (though the virtual memory totals about
3.5GB). Is there another setting that I should consider tweaking which
will actually fully utilize the allotted resources?

A (very) rough comparison: the hsqldb main-memory Java RDBMS can run
jTPCC an order of magnitude faster than mysql. I know hsqldb lacks
durability, but only a WAL would be needed, which (with group commits)
is characterized by largely sequential writes. Ideally, I can bring
mysql to this point -- the database is stored in memory, with only a
WAL producing sequential writes to disk, as opposed to incurring
random seeks due to buffer page flushes.

OTOH, it may be possible that the DB is already entirely in memory,
and the performance difference is due entirely to mysql runtime
overheads. Either way, explanations/hints would be much appreciated.
Thanks in advance.
--
Yang Zhang
http://www.mit.edu/~y_z/

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