xfs: track delayed allocation reservations across the filesystem

Add a percpu counter to track the number of blocks directly reserved for
delayed allocations on the data device.  This counter (in contrast to
i_delayed_blks) does not track allocated CoW staging extents or anything
going on with the realtime device.  It will be used in the upcoming
summary counter scrub function to check the free block counts without
having to freeze the filesystem or walk all the inodes to find the
delayed allocations.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>

1 files changed, 21 insertions, 0 deletions

diff --git a/fs/xfs/xfs_mount.c b/fs/xfs/xfs_mount.c
index eff8b4c3eb3e..4cedf6f8565b 100644
--- a/fs/xfs/xfs_mount.c
+++ b/fs/xfs/xfs_mount.c
@@ -1451,3 +1451,24 @@ xfs_force_summary_recalc(
 
 	xfs_fs_mark_sick(mp, XFS_SICK_FS_COUNTERS);
 }
+
+/*
+ * Update the in-core delayed block counter.
+ *
+ * We prefer to update the counter without having to take a spinlock for every
+ * counter update (i.e. batching).  Each change to delayed allocation
+ * reservations can change can easily exceed the default percpu counter
+ * batching, so we use a larger batch factor here.
+ *
+ * Note that we don't currently have any callers requiring fast summation
+ * (e.g. percpu_counter_read) so we can use a big batch value here.
+ */
+#define XFS_DELALLOC_BATCH	(4096)
+void
+xfs_mod_delalloc(
+	struct xfs_mount	*mp,
+	int64_t			delta)
+{
+	percpu_counter_add_batch(&mp->m_delalloc_blks, delta,
+			XFS_DELALLOC_BATCH);
+}