I can trigger latencies up to ~1.1 ms with a CVS checkout.  It looks
like inside ext3_try_to_allocate_with_rsv, we spend a long time in this
loop:

ext3_test_allocatable (bitmap_search_next_usable_block)
find_next_zero_bit (bitmap_search_next_usable_block)
find_next_zero_bit (bitmap_search_next_usable_block)

ext3_test_allocatable (bitmap_search_next_usable_block)
find_next_zero_bit (bitmap_search_next_usable_block)
find_next_zero_bit (bitmap_search_next_usable_block)

etc.

Lee