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xfs: replace i_flock with a sleeping bitlock

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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>
This commit is contained in:
Christoph Hellwig
2011-12-18 20:00:09 +00:00
committed by Ben Myers
parent 49e4c70e52
commit 474fce0675
6 changed files with 76 additions and 46 deletions
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20
fs/xfs/xfs_iget.c
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@@ -77,7 +77,7 @@ xfs_inode_alloc(
ASSERT(atomic_read(&ip->i_pincount) == 0);
ASSERT(!spin_is_locked(&ip->i_flags_lock));
ASSERT(completion_done(&ip->i_flush));
ASSERT(!xfs_isiflocked(ip));
ASSERT(ip->i_ino == 0);
mrlock_init(&ip->i_iolock, MRLOCK_BARRIER, "xfsio", ip->i_ino);
@@ -150,7 +150,7 @@ xfs_inode_free(
/* asserts to verify all state is correct here */
ASSERT(atomic_read(&ip->i_pincount) == 0);
ASSERT(!spin_is_locked(&ip->i_flags_lock));
ASSERT(completion_done(&ip->i_flush));
ASSERT(!xfs_isiflocked(ip));
/*
* Because we use RCU freeing we need to ensure the inode always
@@ -713,3 +713,19 @@ xfs_isilocked(
return 0;
}
#endif
void
__xfs_iflock(
struct xfs_inode *ip)
{
wait_queue_head_t *wq = bit_waitqueue(&ip->i_flags, __XFS_IFLOCK_BIT);
DEFINE_WAIT_BIT(wait, &ip->i_flags, __XFS_IFLOCK_BIT);
do {
prepare_to_wait_exclusive(wq, &wait.wait, TASK_UNINTERRUPTIBLE);
if (xfs_isiflocked(ip))
io_schedule();
} while (!xfs_iflock_nowait(ip));
finish_wait(wq, &wait.wait);
}