io_uring: shuffle rarely used ctx fields

There is a bunch of scattered around ctx fields that are almost never
used, e.g. only on ring exit, plunge them to the end, better locality,
better aesthetically.
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/782ff94b00355923eae757d58b1a47821b5b46d4.1621201931.git.asml.silence@gmail.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -368,9 +368,6 @@ struct io_ring_ctx {
 		unsigned		cached_cq_overflow;
 		unsigned long		sq_check_overflow;
 
-		/* hashed buffered write serialization */
-		struct io_wq_hash	*hash_map;
-
 		struct list_head	defer_list;
 		struct list_head	timeout_list;
 		struct list_head	cq_overflow_list;
@@ -387,9 +384,6 @@ struct io_ring_ctx {
 
 	struct io_rings	*rings;
 
-	/* Only used for accounting purposes */
-	struct mm_struct	*mm_account;
-
 	const struct cred	*sq_creds;	/* cred used for __io_sq_thread() */
 	struct io_sq_data	*sq_data;	/* if using sq thread polling */
 
@@ -410,14 +404,6 @@ struct io_ring_ctx {
 	unsigned		nr_user_bufs;
 	struct io_mapped_ubuf	**user_bufs;
 
-	struct user_struct	*user;
-
-	struct completion	ref_comp;
-
-#if defined(CONFIG_UNIX)
-	struct socket		*ring_sock;
-#endif
-
 	struct xarray		io_buffers;
 
 	struct xarray		personalities;
@@ -461,12 +447,24 @@ struct io_ring_ctx {
 
 	struct io_restriction		restrictions;
 
-	/* exit task_work */
-	struct callback_head		*exit_task_work;
-
 	/* Keep this last, we don't need it for the fast path */
-	struct work_struct		exit_work;
-	struct list_head		tctx_list;
+	struct {
+		#if defined(CONFIG_UNIX)
+			struct socket		*ring_sock;
+		#endif
+		/* hashed buffered write serialization */
+		struct io_wq_hash		*hash_map;
+
+		/* Only used for accounting purposes */
+		struct user_struct		*user;
+		struct mm_struct		*mm_account;
+
+		/* ctx exit and cancelation */
+		struct callback_head		*exit_task_work;
+		struct work_struct		exit_work;
+		struct list_head		tctx_list;
+		struct completion		ref_comp;
+	};
 };
 
 struct io_uring_task {