952b7d192b
Enhance bin run deallocation to avoid marking all pages as dirty, since the
dirty bits are already correct for all but the first page, due to the use of
arena_run_rc_{incr,decr}(). This tends to dramatically reduce the number of
pages that are marked dirty.
Modify arena_bin_run_size_calc() to assure that bin run headers never exceed
one page. In practice, this can't happen unless hard-coded constants (related
to RUN_MAX_OVRHD) are modified, but the dirty page tracking code assumes bin
run headers never extend past the first page, so it seems worth making this a
universally valid assumption.