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>
diff --git a/fs/xfs/xfs_sync.c b/fs/xfs/xfs_sync.c
index 72c01a1..40b75ee 100644
--- a/fs/xfs/xfs_sync.c
+++ b/fs/xfs/xfs_sync.c
@@ -707,14 +707,13 @@
return 1;
/*
- * do some unlocked checks first to avoid unnecessary lock traffic.
- * The first is a flush lock check, the second is a already in reclaim
- * check. Only do these checks if we are not going to block on locks.
+ * If we are asked for non-blocking operation, do unlocked checks to
+ * see if the inode already is being flushed or in reclaim to avoid
+ * lock traffic.
*/
if ((flags & SYNC_TRYLOCK) &&
- (!ip->i_flush.done || __xfs_iflags_test(ip, XFS_IRECLAIM))) {
+ __xfs_iflags_test(ip, XFS_IFLOCK | XFS_IRECLAIM))
return 1;
- }
/*
* The radix tree lock here protects a thread in xfs_iget from racing