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Commit b2ac2ea6 authored by Davidlohr Bueso's avatar Davidlohr Bueso Committed by Linus Torvalds
Browse files

fs/epoll: use faster rb_first_cached() 

...  such that we can avoid the tree walks to get the node with the
smallest key.  Semantically the same, as the previously used rb_first(),
but O(1).  The main overhead is the extra footprint for the cached rb_node
pointer, which should not matter for epoll.

Link: http://lkml.kernel.org/r/20170719014603.19029-15-dave@stgolabs.net


Signed-off-by: default avatarDavidlohr Bueso <dbueso@suse.de>
Acked-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Jan Kara <jack@suse.cz>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 410bd5ec

fs/eventpoll.c

+16 −14
Original line number Diff line number Diff line
@@ -205,7 +205,7 @@ struct eventpoll { 
	struct list_head rdllist;



	/* RB tree root used to store monitored fd structs */

	struct rb_root rbr;

	struct rb_root_cached rbr;



	/*

	 * This is a single linked list that chains all the "struct epitem" that
@@ -796,7 +796,7 @@ static int ep_remove(struct eventpoll *ep, struct epitem *epi) 
	list_del_rcu(&epi->fllink);

	spin_unlock(&file->f_lock);



	rb_erase(&epi->rbn, &ep->rbr);

	rb_erase_cached(&epi->rbn, &ep->rbr);



	spin_lock_irqsave(&ep->lock, flags);

	if (ep_is_linked(&epi->rdllink))
@@ -840,7 +840,7 @@ static void ep_free(struct eventpoll *ep) 
	/*

	 * Walks through the whole tree by unregistering poll callbacks.

	 */

	for (rbp = rb_first(&ep->rbr); rbp; rbp = rb_next(rbp)) {

	for (rbp = rb_first_cached(&ep->rbr); rbp; rbp = rb_next(rbp)) {

		epi = rb_entry(rbp, struct epitem, rbn);



		ep_unregister_pollwait(ep, epi);
@@ -856,7 +856,7 @@ static void ep_free(struct eventpoll *ep) 
	 * a lockdep warning.

	 */

	mutex_lock(&ep->mtx);

	while ((rbp = rb_first(&ep->rbr)) != NULL) {

	while ((rbp = rb_first_cached(&ep->rbr)) != NULL) {

		epi = rb_entry(rbp, struct epitem, rbn);

		ep_remove(ep, epi);

		cond_resched();
@@ -963,7 +963,7 @@ static void ep_show_fdinfo(struct seq_file *m, struct file *f) 
	struct rb_node *rbp;



	mutex_lock(&ep->mtx);

	for (rbp = rb_first(&ep->rbr); rbp; rbp = rb_next(rbp)) {

	for (rbp = rb_first_cached(&ep->rbr); rbp; rbp = rb_next(rbp)) {

		struct epitem *epi = rb_entry(rbp, struct epitem, rbn);

		struct inode *inode = file_inode(epi->ffd.file);
@@ -1040,7 +1040,7 @@ static int ep_alloc(struct eventpoll **pep) 
	init_waitqueue_head(&ep->wq);

	init_waitqueue_head(&ep->poll_wait);

	INIT_LIST_HEAD(&ep->rdllist);

	ep->rbr = RB_ROOT;

	ep->rbr = RB_ROOT_CACHED;

	ep->ovflist = EP_UNACTIVE_PTR;

	ep->user = user;
@@ -1066,7 +1066,7 @@ static struct epitem *ep_find(struct eventpoll *ep, struct file *file, int fd) 
	struct epoll_filefd ffd;



	ep_set_ffd(&ffd, file, fd);

	for (rbp = ep->rbr.rb_node; rbp; ) {

	for (rbp = ep->rbr.rb_root.rb_node; rbp; ) {

		epi = rb_entry(rbp, struct epitem, rbn);

		kcmp = ep_cmp_ffd(&ffd, &epi->ffd);

		if (kcmp > 0)
@@ -1088,7 +1088,7 @@ static struct epitem *ep_find_tfd(struct eventpoll *ep, int tfd, unsigned long t 
	struct rb_node *rbp;

	struct epitem *epi;



	for (rbp = rb_first(&ep->rbr); rbp; rbp = rb_next(rbp)) {

	for (rbp = rb_first_cached(&ep->rbr); rbp; rbp = rb_next(rbp)) {

		epi = rb_entry(rbp, struct epitem, rbn);

		if (epi->ffd.fd == tfd) {

			if (toff == 0)
@@ -1273,20 +1273,22 @@ static void ep_ptable_queue_proc(struct file *file, wait_queue_head_t *whead, 
static void ep_rbtree_insert(struct eventpoll *ep, struct epitem *epi)

{

	int kcmp;

	struct rb_node **p = &ep->rbr.rb_node, *parent = NULL;

	struct rb_node **p = &ep->rbr.rb_root.rb_node, *parent = NULL;

	struct epitem *epic;

	bool leftmost = true;



	while (*p) {

		parent = *p;

		epic = rb_entry(parent, struct epitem, rbn);

		kcmp = ep_cmp_ffd(&epi->ffd, &epic->ffd);

		if (kcmp > 0)

		if (kcmp > 0) {

			p = &parent->rb_right;

		else

			leftmost = false;

		} else

			p = &parent->rb_left;

	}

	rb_link_node(&epi->rbn, parent, p);

	rb_insert_color(&epi->rbn, &ep->rbr);

	rb_insert_color_cached(&epi->rbn, &ep->rbr, leftmost);

}
@@ -1530,7 +1532,7 @@ static int ep_insert(struct eventpoll *ep, struct epoll_event *event, 
	list_del_rcu(&epi->fllink);

	spin_unlock(&tfile->f_lock);



	rb_erase(&epi->rbn, &ep->rbr);

	rb_erase_cached(&epi->rbn, &ep->rbr);



error_unregister:

	ep_unregister_pollwait(ep, epi);
@@ -1878,7 +1880,7 @@ static int ep_loop_check_proc(void *priv, void *cookie, int call_nests) 
	mutex_lock_nested(&ep->mtx, call_nests + 1);

	ep->visited = 1;

	list_add(&ep->visited_list_link, &visited_list);

	for (rbp = rb_first(&ep->rbr); rbp; rbp = rb_next(rbp)) {

	for (rbp = rb_first_cached(&ep->rbr); rbp; rbp = rb_next(rbp)) {

		epi = rb_entry(rbp, struct epitem, rbn);

		if (unlikely(is_file_epoll(epi->ffd.file))) {

			ep_tovisit = epi->ffd.file->private_data;