This looks pretty good. Did this past xfstests? I'd also like to add
tests actually executing this code path just, to be sure. E.g. variants
of aio-stress actually using O_SYNC. We can't easily test data really
made it to disk that way, although at least we make sure the code
doesn't break.
On Fri, Jan 27, 2012 at 04:15:47PM -0500, Jeff Moyer wrote:
> Hi,
>
> If a file is opened with O_SYNC|O_DIRECT, the drive cache does not get
> flushed after the write completion. Instead, it's flushed *before* the
> I/O is sent to the disk (in __generic_file_aio_write).
XFS doesn't actually use __generic_file_aio_write, so this sentence
isn't correct for XFS.
> + } else if (xfs_ioend_needs_cache_flush(ioend)) {
> + struct xfs_inode *ip = XFS_I(ioend->io_inode);
> + struct xfs_mount *mp = ip->i_mount;
> + int err;
> + int log_flushed = 0;
> +
> + /*
> + * Check to see if we only need to sync data. If so,
> + * we can skip the log flush.
> + */
> + if (IS_SYNC(ioend->io_inode) ||
> + (ioend->io_iocb->ki_filp->f_flags & __O_SYNC)) {
> + err = _xfs_log_force(mp, XFS_LOG_SYNC, &log_flushed);
Can you add a TODO comment that this actually is synchronous and thus
will block the I/O completion work queue?
Also you can use _xfs_log_force_lsn here as don't need to flush the
whole log, just up to the last lsn that touched the inode. Copy, or
better factor the code from xfs_dir_fsync for that.
Last but not least this won't catch timestamp updates. Given that I'm
about to send a series making timestamp updates transaction I would not
recommend you to bother with that, but if you want to take a look
at how xfs_file_fsync deals with them. Given that this series touches
the same area I'd also like to take your xfs patch in through the xfs tree
to avoid conflicts.
> @@ -47,6 +47,7 @@ STATIC int xfsbufd(void *);
> static struct workqueue_struct *xfslogd_workqueue;
> struct workqueue_struct *xfsdatad_workqueue;
> struct workqueue_struct *xfsconvertd_workqueue;
> +struct workqueue_struct *xfsflushd_workqueue;
>
> #ifdef XFS_BUF_LOCK_TRACKING
> # define XB_SET_OWNER(bp) ((bp)->b_last_holder = current->pid)
> @@ -1802,8 +1803,15 @@ xfs_buf_init(void)
> if (!xfsconvertd_workqueue)
> goto out_destroy_xfsdatad_workqueue;
>
> + xfsflushd_workqueue = alloc_workqueue("xfsflushd",
> + WQ_MEM_RECLAIM, 1);
This should allow a higher concurrently level, it's probably a good
idea to pass 0 and use the default.
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