fs/epoll: remove max_nests argument from ep_call_nested()

Patch series "epoll: some miscellaneous optimizations".

The following are some incremental optimizations on some of the epoll
core.  Each patch has the details, but together, the series is seen to
shave off measurable cycles on a number of systems and workloads.

For example, on a 40-core IB, a pipetest as well as parallel
epoll_wait() benchmark show around a 20-30% increase in raw operations
per second when the box is fully occupied (incremental thread counts),
and up to 15% performance improvement with lower counts.

Passes ltp epoll related testcases.

This patch(of 6):

All callers pass the EP_MAX_NESTS constant already, so lets simplify
this a tad and get rid of the redundant parameter for nested eventpolls.

Link: http://lkml.kernel.org/r/20181108051006.18751-2-dave@stgolabs.netSigned-off-by: Davidlohr Bueso <dbueso@suse.de>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Jason Baron <jbaron@akamai.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/eventpoll.c

@@ -471,7 +471,6 @@ static inline void ep_set_busy_poll_napi_id(struct epitem *epi)
  *                  no re-entered.
  *
  * @ncalls: Pointer to the nested_calls structure to be used for this call.
- * @max_nests: Maximum number of allowed nesting calls.
  * @nproc: Nested call core function pointer.
  * @priv: Opaque data to be passed to the @nproc callback.
  * @cookie: Cookie to be used to identify this nested call.
@@ -480,7 +479,7 @@ static inline void ep_set_busy_poll_napi_id(struct epitem *epi)
  * Returns: Returns the code returned by the @nproc callback, or -1 if
  *          the maximum recursion limit has been exceeded.
  */
-static int ep_call_nested(struct nested_calls *ncalls, int max_nests,
+static int ep_call_nested(struct nested_calls *ncalls,
 			  int (*nproc)(void *, void *, int), void *priv,
 			  void *cookie, void *ctx)
 {
@@ -499,7 +498,7 @@ static int ep_call_nested(struct nested_calls *ncalls, int max_nests,
 	 */
 	list_for_each_entry(tncur, lsthead, llink) {
 		if (tncur->ctx == ctx &&
-		    (tncur->cookie == cookie || ++call_nests > max_nests)) {
+		    (tncur->cookie == cookie || ++call_nests > EP_MAX_NESTS)) {
 			/*
 			 * Ops ... loop detected or maximum nest level reached.
 			 * We abort this wake by breaking the cycle itself.
@@ -573,7 +572,7 @@ static void ep_poll_safewake(wait_queue_head_t *wq)
 {
 	int this_cpu = get_cpu();
 
-	ep_call_nested(&poll_safewake_ncalls, EP_MAX_NESTS,
+	ep_call_nested(&poll_safewake_ncalls,
 		       ep_poll_wakeup_proc, NULL, wq, (void *) (long) this_cpu);
 
 	put_cpu();
@@ -1333,7 +1332,6 @@ static int reverse_path_check_proc(void *priv, void *cookie, int call_nests)
 				}
 			} else {
 				error = ep_call_nested(&poll_loop_ncalls,
-							EP_MAX_NESTS,
 							reverse_path_check_proc,
 							child_file, child_file,
 							current);
@@ -1367,7 +1365,7 @@ static int reverse_path_check(void)
 	/* let's call this for all tfiles */
 	list_for_each_entry(current_file, &tfile_check_list, f_tfile_llink) {
 		path_count_init();
-		error = ep_call_nested(&poll_loop_ncalls, EP_MAX_NESTS,
+		error = ep_call_nested(&poll_loop_ncalls,
 					reverse_path_check_proc, current_file,
 					current_file, current);
 		if (error)
@@ -1876,7 +1874,7 @@ static int ep_loop_check_proc(void *priv, void *cookie, int call_nests)
 			ep_tovisit = epi->ffd.file->private_data;
 			if (ep_tovisit->visited)
 				continue;
-			error = ep_call_nested(&poll_loop_ncalls, EP_MAX_NESTS,
+			error = ep_call_nested(&poll_loop_ncalls,
 					ep_loop_check_proc, epi->ffd.file,
 					ep_tovisit, current);
 			if (error != 0)
@@ -1916,7 +1914,7 @@ static int ep_loop_check(struct eventpoll *ep, struct file *file)
 	int ret;
 	struct eventpoll *ep_cur, *ep_next;
 
-	ret = ep_call_nested(&poll_loop_ncalls, EP_MAX_NESTS,
+	ret = ep_call_nested(&poll_loop_ncalls,
 			      ep_loop_check_proc, file, ep, current);
 	/* clear visited list */
 	list_for_each_entry_safe(ep_cur, ep_next, &visited_list,