1 files changed, 6 insertions, 2 deletions

diff --git a/include/linux/idr.h b/include/linux/idr.h
index cdb715e58e3e..13a801f3d028 100644
--- a/include/linux/idr.h
+++ b/include/linux/idr.h
@@ -81,6 +81,7 @@ struct idr {
 #define _idr_rc_to_errno(rc) ((rc) == -1 ? -EAGAIN : -ENOSPC)
 
 /**
+ * DOC: idr sync
  * idr synchronization (stolen from radix-tree.h)
  *
  * idr_find() is able to be called locklessly, using RCU. The caller must
@@ -117,10 +118,13 @@ void idr_init(struct idr *idp);
 /*
  * IDA - IDR based id allocator, use when translation from id to
  * pointer isn't necessary.
+ *
+ * IDA_BITMAP_LONGS is calculated to be one less to accommodate
+ * ida_bitmap->nr_busy so that the whole struct fits in 128 bytes.
  */
 #define IDA_CHUNK_SIZE          128     /* 128 bytes per chunk */
-#define IDA_BITMAP_LONGS        (128 / sizeof(long) - 1)
-#define IDA_BITMAP_BITS         (IDA_BITMAP_LONGS * sizeof(long) * 8)
+#define IDA_BITMAP_LONGS        (IDA_CHUNK_SIZE / sizeof(long) - 1)
+#define IDA_BITMAP_BITS         (IDA_BITMAP_LONGS * sizeof(long) * 8)
 
 struct ida_bitmap {
         long                    nr_busy;