ext4: address scalability issue by removing extent cache statistics

commit 9cd70b347e9761ea2d2ac3d758c529a48a8193e6 upstream.

Andi Kleen and Tim Chen have reported that under certain circumstances
the extent cache statistics are causing scalability problems due to
cache line bounces.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --cc fs/ext4/ext4.h
Simple merge

diff --cc fs/ext4/extents.c
Simple merge

diff --cc fs/ext4/super.c
Simple merge