Journal replay will be run when performing recovery for a dead node.  To
avoid the stale cache impact, all blocks of dead node's journal inode
were reloaded from disk.  This hurts the performance.  Check whether one
block is cached before reloading it can improve performance a lot.  In
my test env, the time doing recovery was improved from 120s to 1s.

[akpm@linux-foundation.org: clean up the for loop p_blkno handling]
Link: http://lkml.kernel.org/r/1466155682-24656-1-git-send-email-junxiao.bi@oracle.comSigned-off-by: Junxiao Bi <junxiao.bi@oracle.com>
Reviewed-by: Joseph Qi <joseph.qi@huawei.com>
Cc: "Gang He" <ghe@suse.com>
Cc: Mark Fasheh <mfasheh@suse.de>
Cc: Joel Becker <jlbec@evilplan.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>