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[PATCH 1/3] xfs: honor the O_SYNC flag for aysnchronous direct I/O reque

To: linux-ext4@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx, linux-fsdevel@xxxxxxxxxxxxxxx
Subject: [PATCH 1/3] xfs: honor the O_SYNC flag for aysnchronous direct I/O requests
From: Jeff Moyer <jmoyer@xxxxxxxxxx>
Date: Fri, 27 Jan 2012 16:15:47 -0500
Cc: Jeff Moyer <jmoyer@xxxxxxxxxx>
In-reply-to: <1327698949-12616-1-git-send-email-jmoyer@xxxxxxxxxx>
References: <1327698949-12616-1-git-send-email-jmoyer@xxxxxxxxxx>
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).  This patch
attempts to fix that problem by marking an I/O as requiring a cache
flush in endio processing.  I'll send a follow-on patch to the
generic write code to get rid of the bogus generic_write_sync call
when EIOCBQUEUED is returned.

Signed-off-by: Jeff Moyer <jmoyer@xxxxxxxxxx>
---
 fs/xfs/xfs_aops.c |   69 +++++++++++++++++++++++++++++++++++++++++++++++++++-
 fs/xfs/xfs_aops.h |    1 +
 fs/xfs/xfs_buf.c  |    9 +++++++
 3 files changed, 77 insertions(+), 2 deletions(-)

diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
index 574d4ee..909e020 100644
--- a/fs/xfs/xfs_aops.c
+++ b/fs/xfs/xfs_aops.c
@@ -158,6 +158,48 @@ xfs_setfilesize(
 }
 
 /*
+ * In the case of synchronous, AIO, O_DIRECT writes, we need to flush
+ * the disk cache when the I/O is complete.
+ */
+STATIC bool
+xfs_ioend_needs_cache_flush(
+       struct xfs_ioend        *ioend)
+{
+       if (!ioend->io_isasync)
+               return false;
+
+       return (IS_SYNC(ioend->io_inode) ||
+               (ioend->io_iocb->ki_filp->f_flags & O_DSYNC));
+}
+
+STATIC void
+xfs_end_io_flush(
+       struct bio      *bio,
+       int             error)
+{
+       struct xfs_ioend *ioend = bio->bi_private;
+
+       if (error && ioend->io_result > 0)
+               ioend->io_result = error;
+
+       xfs_destroy_ioend(ioend);
+       bio_put(bio);
+}
+
+STATIC void
+xfs_ioend_flush_cache(
+       struct xfs_ioend        *ioend)
+{
+       struct bio *bio;
+
+       bio = bio_alloc(GFP_KERNEL, 0);
+       bio->bi_end_io = xfs_end_io_flush;
+       bio->bi_bdev = xfs_find_bdev_for_inode(ioend->io_inode);
+       bio->bi_private = ioend;
+       submit_bio(WRITE_FLUSH, bio);
+}
+
+/*
  * Schedule IO completion handling on the final put of an ioend.
  *
  * If there is no work to do we might as well call it a day and free the
@@ -172,6 +214,8 @@ xfs_finish_ioend(
                        queue_work(xfsconvertd_workqueue, &ioend->io_work);
                else if (xfs_ioend_is_append(ioend))
                        queue_work(xfsdatad_workqueue, &ioend->io_work);
+               else if (xfs_ioend_needs_cache_flush(ioend))
+                       queue_work(xfsflushd_workqueue, &ioend->io_work);
                else
                        xfs_destroy_ioend(ioend);
        }
@@ -226,9 +270,30 @@ done:
                xfs_finish_ioend(ioend);
                /* ensure we don't spin on blocked ioends */
                delay(1);
-       } else {
+       } 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);
+                       if (err && ioend->io_result > 0)
+                               ioend->io_result = err;
+                       if (err || log_flushed) {
+                               xfs_destroy_ioend(ioend);
+                               return;
+                       }
+               }
+               /* log not flushed or data sync only, flush the disk cache */
+               xfs_ioend_flush_cache(ioend);
+       } else
                xfs_destroy_ioend(ioend);
-       }
 }
 
 /*
diff --git a/fs/xfs/xfs_aops.h b/fs/xfs/xfs_aops.h
index 116dd5c..3f4a1c4 100644
--- a/fs/xfs/xfs_aops.h
+++ b/fs/xfs/xfs_aops.h
@@ -20,6 +20,7 @@
 
 extern struct workqueue_struct *xfsdatad_workqueue;
 extern struct workqueue_struct *xfsconvertd_workqueue;
+extern struct workqueue_struct *xfsflushd_workqueue;
 extern mempool_t *xfs_ioend_pool;
 
 /*
diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
index 4dff85c..39980a8 100644
--- a/fs/xfs/xfs_buf.c
+++ b/fs/xfs/xfs_buf.c
@@ -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);
+       if (!xfsflushd_workqueue)
+               goto out_destroy_xfsconvertd_workqueue;
+
        return 0;
 
+ out_destroy_xfsconvertd_workqueue:
+       destroy_workqueue(xfsconvertd_workqueue);
  out_destroy_xfsdatad_workqueue:
        destroy_workqueue(xfsdatad_workqueue);
  out_destroy_xfslogd_workqueue:
@@ -1817,6 +1825,7 @@ xfs_buf_init(void)
 void
 xfs_buf_terminate(void)
 {
+       destroy_workqueue(xfsflushd_workqueue);
        destroy_workqueue(xfsconvertd_workqueue);
        destroy_workqueue(xfsdatad_workqueue);
        destroy_workqueue(xfslogd_workqueue);
-- 
1.7.1

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