On Tue, Oct 18, 2011 at 04:13:06PM -0400, Christoph Hellwig wrote:
> 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 a faster 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@xxxxxx>
.....
> @@ -716,3 +716,19 @@ xfs_isilocked(
> return 0;
> }
> #endif
> +
> +void
> +__xfs_iflock(
> + struct xfs_inode *ip)
> +{
> + wait_queue_head_t *wq = bit_waitqueue(&ip->i_flags, __XFS_IFLOCK);
> + DEFINE_WAIT_BIT(wait, &ip->i_flags, __XFS_IFLOCK);
> +
> + do {
> + prepare_to_wait_exclusive(wq, &wait.wait, TASK_UNINTERRUPTIBLE);
> + if (xfs_isiflocked(ip))
> + schedule();
> + } while (!xfs_iflock_nowait(ip));
> +
> + finish_wait(wq, &wait.wait);
> +}
Given that the only way that the inode will become unlocked is for
IO to complete, that makes this an IO wait, right? Perhaps this
should call io_schedule() in that case?
> @@ -380,6 +372,8 @@ static inline void xfs_ifunlock(xfs_inod
> #define XFS_IFILESTREAM 0x0010 /* inode is in a filestream directory */
> #define XFS_ITRUNCATED 0x0020 /* truncated down so flush-on-close */
> #define XFS_IDIRTY_RELEASE 0x0040 /* dirty release already seen */
> +#define __XFS_IFLOCK 8 /* inode is beeing flushed right now */
> +#define XFS_IFLOCK (1 << __XFS_IFLOCK)
Any reason for leaving a gap in the flag space here?
Otherwise looks good.
Reviewed-by: Dave Chinner <dchinner@xxxxxxxxxx>
--
Dave Chinner
david@xxxxxxxxxxxxx
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