xfs: implement the lazytime mount option

Use the VFS dirty inode tracking for lazytime inodes only, and just
log them in ->dirty_inode.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

fs/xfs/xfs_iops.c

@@ -46,6 +46,7 @@
 #include <linux/security.h>
 #include <linux/iomap.h>
 #include <linux/slab.h>
+#include <linux/iversion.h>
 
 /*
  * Directories have different lock order w.r.t. mmap_sem compared to regular
@@ -1052,11 +1053,21 @@ xfs_vn_update_time(
 {
 	struct xfs_inode	*ip = XFS_I(inode);
 	struct xfs_mount	*mp = ip->i_mount;
+	int			log_flags = XFS_ILOG_TIMESTAMP;
 	struct xfs_trans	*tp;
 	int			error;
 
 	trace_xfs_update_time(ip);
 
+	if (inode->i_sb->s_flags & SB_LAZYTIME) {
+		if (!((flags & S_VERSION) &&
+		      inode_maybe_inc_iversion(inode, false)))
+			return generic_update_time(inode, now, flags);
+
+		/* Capture the iversion update that just occurred */
+		log_flags |= XFS_ILOG_CORE;
+	}
+
 	error = xfs_trans_alloc(mp, &M_RES(mp)->tr_fsyncts, 0, 0, 0, &tp);
 	if (error)
 		return error;
@@ -1070,7 +1081,7 @@ xfs_vn_update_time(
 		inode->i_atime = *now;
 
 	xfs_trans_ijoin(tp, ip, XFS_ILOCK_EXCL);
-	xfs_trans_log_inode(tp, ip, XFS_ILOG_TIMESTAMP);
+	xfs_trans_log_inode(tp, ip, log_flags);
 	return xfs_trans_commit(tp);
 }
 

fs/xfs/xfs_super.c

@@ -1009,6 +1009,28 @@ xfs_fs_destroy_inode(
 	xfs_inode_set_reclaim_tag(ip);
 }
 
+static void
+xfs_fs_dirty_inode(
+	struct inode			*inode,
+	int				flag)
+{
+	struct xfs_inode		*ip = XFS_I(inode);
+	struct xfs_mount		*mp = ip->i_mount;
+	struct xfs_trans		*tp;
+
+	if (!(inode->i_sb->s_flags & SB_LAZYTIME))
+		return;
+	if (flag != I_DIRTY_SYNC || !(inode->i_state & I_DIRTY_TIME))
+		return;
+
+	if (xfs_trans_alloc(mp, &M_RES(mp)->tr_fsyncts, 0, 0, 0, &tp))
+		return;
+	xfs_ilock(ip, XFS_ILOCK_EXCL);
+	xfs_trans_ijoin(tp, ip, XFS_ILOCK_EXCL);
+	xfs_trans_log_inode(tp, ip, XFS_ILOG_TIMESTAMP);
+	xfs_trans_commit(tp);
+}
+
 /*
  * Slab object creation initialisation for the XFS inode.
  * This covers only the idempotent fields in the XFS inode;
@@ -1789,6 +1811,7 @@ xfs_fs_free_cached_objects(
 static const struct super_operations xfs_super_operations = {
 	.alloc_inode		= xfs_fs_alloc_inode,
 	.destroy_inode		= xfs_fs_destroy_inode,
+	.dirty_inode		= xfs_fs_dirty_inode,
 	.drop_inode		= xfs_fs_drop_inode,
 	.put_super		= xfs_fs_put_super,
 	.sync_fs		= xfs_fs_sync_fs,

fs/xfs/xfs_trans_inode.c

@@ -98,9 +98,23 @@ xfs_trans_log_inode(
 	xfs_inode_t	*ip,
 	uint		flags)
 {
+	struct inode	*inode = VFS_I(ip);
+
 	ASSERT(ip->i_itemp != NULL);
 	ASSERT(xfs_isilocked(ip, XFS_ILOCK_EXCL));
 
+	/*
+	 * Don't bother with i_lock for the I_DIRTY_TIME check here, as races
+	 * don't matter - we either will need an extra transaction in 24 hours
+	 * to log the timestamps, or will clear already cleared fields in the
+	 * worst case.
+	 */
+	if (inode->i_state & (I_DIRTY_TIME | I_DIRTY_TIME_EXPIRED)) {
+		spin_lock(&inode->i_lock);
+		inode->i_state &= ~(I_DIRTY_TIME | I_DIRTY_TIME_EXPIRED);
+		spin_unlock(&inode->i_lock);
+	}
+
 	/*
 	 * Record the specific change for fdatasync optimisation. This
 	 * allows fdatasync to skip log forces for inodes that are only