xfs: replace i_flock with a sleeping bitlock

We almost never block on i_flock, the exception is synchronous inode
flushing.  Instead of bloating the inode with a 16/24-byte completion
that we abuse as a semaphore just implement it as a bitlock that uses
a bit waitqueue for the rare sleeping path.  This primarily is a
tradeoff between a much smaller inode and a faster non-blocking
path vs faster wakeups, and we are much better off with the former.

A small downside is that we will lose lockdep checking for i_flock, but
given that it's always taken inside the ilock that should be acceptable.

Note that for example the inode writeback locking is implemented in a
very similar way.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Alex Elder <aelder@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>

1 files changed, 0 insertions, 7 deletions

diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
index 281961c1d81a..6851fa7b1afa 100644
--- a/fs/xfs/xfs_super.c
+++ b/fs/xfs/xfs_super.c
@@ -829,13 +829,6 @@ xfs_fs_inode_init_once(
         atomic_set(&ip->i_pincount, 0);
         spin_lock_init(&ip->i_flags_lock);
         init_waitqueue_head(&ip->i_ipin_wait);
-        /*
-         * Because we want to use a counting completion, complete
-         * the flush completion once to allow a single access to
-         * the flush completion without blocking.
-         */
-        init_completion(&ip->i_flush);
-        complete(&ip->i_flush);
 
         mrlock_init(&ip->i_lock, MRLOCK_ALLOW_EQUAL_PRI|MRLOCK_BARRIER,
                      "xfsino", ip->i_ino);