Merely removing down_read(&mm->mmap_sem) from task_vsize() is too
half-assed to let stand. The following patch removes the vma iteration
as well as the down_read(&mm->mmap_sem) from both task_mem() and
task_statm() and callers for the CONFIG_MMU=y case in favor of
accounting the various stats reported at the times of vma creation,
destruction, and modification. Unlike the 2.4.x patches of the same
name, this has no per-pte-modification overhead whatsoever.

This patch quashes end user complaints of top(1) being slow as well as
kernel hacker complaints of per-pte accounting overhead simultaneously.
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>