[PATCH 45/58] xfs: create a separate workqueue for copy-on-write activities

["Darrick J. Wong" <darrick.wong@xxxxxxxxxx>]

Create a separate workqueue to handle copy on write blocks so that we
don't explode the number of kworkers if a flood of writes comes
through.  We could possibly use m_buf_wq for this too...

Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
---
 fs/xfs/xfs_mount.h |    1 +
 fs/xfs/xfs_super.c |   36 +++++++++++++++++++++++++++++++++++-
 2 files changed, 36 insertions(+), 1 deletion(-)


diff --git a/fs/xfs/xfs_mount.h b/fs/xfs/xfs_mount.h
index aba42d7..6f4c335 100644
--- a/fs/xfs/xfs_mount.h
+++ b/fs/xfs/xfs_mount.h
@@ -142,6 +142,7 @@ typedef struct xfs_mount {
        struct workqueue_struct *m_reclaim_workqueue;
        struct workqueue_struct *m_log_workqueue;
        struct workqueue_struct *m_eofblocks_workqueue;
+       struct workqueue_struct *m_cow_workqueue;
 
        /*
         * Generation of the filesysyem layout.  This is incremented by each
diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
index 6dc5993..c6a26b0 100644
--- a/fs/xfs/xfs_super.c
+++ b/fs/xfs/xfs_super.c
@@ -883,6 +883,33 @@ xfs_destroy_mount_workqueues(
        destroy_workqueue(mp->m_buf_workqueue);
 }
 
+STATIC int
+xfs_init_feature_workqueues(
+       struct xfs_mount        *mp)
+{
+       if (xfs_sb_version_hasreflink(&mp->m_sb)) {
+               /* XXX awful, but it'll improve when bh's go away */
+               /* XXX probably need locking around the endio rbtree */
+               mp->m_cow_workqueue = alloc_workqueue("xfs-cow/%s",
+                               WQ_MEM_RECLAIM|WQ_FREEZABLE|WQ_UNBOUND,
+                               1, mp->m_fsname);
+               if (!mp->m_cow_workqueue)
+                       goto out;
+       }
+
+       return 0;
+out:
+       return -ENOMEM;
+}
+
+STATIC void
+xfs_destroy_feature_workqueues(
+       struct xfs_mount        *mp)
+{
+       if (mp->m_cow_workqueue)
+               destroy_workqueue(mp->m_cow_workqueue);
+}
+
 /*
  * Flush all dirty data to disk. Must not be called while holding an XFS_ILOCK
  * or a page lock. We use sync_inodes_sb() here to ensure we block while 
waiting
@@ -1490,6 +1517,10 @@ xfs_fs_fill_super(
        if (error)
                goto out_free_sb;
 
+       error = xfs_init_feature_workqueues(mp);
+       if (error)
+               goto out_filestream_unmount;
+
        /*
         * we must configure the block size in the superblock before we run the
         * full mount process as the mount process can lookup and cache inodes.
@@ -1526,7 +1557,7 @@ xfs_fs_fill_super(
 
        error = xfs_mountfs(mp);
        if (error)
-               goto out_filestream_unmount;
+               goto out_destroy_feature_workqueues;
 
        root = igrab(VFS_I(mp->m_rootip));
        if (!root) {
@@ -1541,6 +1572,8 @@ xfs_fs_fill_super(
 
        return 0;
 
+out_destroy_feature_workqueues:
+       xfs_destroy_feature_workqueues(mp);
  out_filestream_unmount:
        xfs_filestream_unmount(mp);
  out_free_sb:
@@ -1570,6 +1603,7 @@ xfs_fs_put_super(
        struct xfs_mount        *mp = XFS_M(sb);
 
        xfs_notice(mp, "Unmounting Filesystem");
+       xfs_destroy_feature_workqueues(mp);
        xfs_filestream_unmount(mp);
        xfs_unmountfs(mp);