[RFC PATCH 01/27] epoll: switch epitem->pwqlist to single-linked list

Al Viro
2020-10-04T02:39:33Z

We only traverse it once to destroy all associated eppoll_entry at
epitem destruction time. The order of traversal is irrelevant there.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
fs/eventpoll.c | 51 +++++++++++++++++++++++++--------------------------
1 file changed, 25 insertions(+), 26 deletions(-)

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 4df61129566d..ae41868d9b35 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -128,6 +128,24 @@ struct nested_calls {
spinlock_t lock;
};

+/* Wait structure used by the poll hooks */
+struct eppoll_entry {
+ /* List header used to link this structure to the "struct epitem" */
+ struct eppoll_entry *next;
+
+ /* The "base" pointer is set to the container "struct epitem" */
+ struct epitem *base;
+
+ /*
+ * Wait queue item that will be linked to the target file wait
+ * queue head.
+ */
+ wait_queue_entry_t wait;
+
+ /* The wait queue head that linked the "wait" wait queue item */
+ wait_queue_head_t *whead;
+};
+
/*
* Each file descriptor added to the eventpoll interface will
* have an entry of this type linked to the "rbr" RB tree.
@@ -158,7 +176,7 @@ struct epitem {
int nwait;

/* List containing poll wait queues */
- struct list_head pwqlist;
+ struct eppoll_entry *pwqlist;

/* The "container" of this item */
struct eventpoll *ep;
@@ -231,24 +249,6 @@ struct eventpoll {
#endif
};

-/* Wait structure used by the poll hooks */
-struct eppoll_entry {
- /* List header used to link this structure to the "struct epitem" */
- struct list_head llink;
-
- /* The "base" pointer is set to the container "struct epitem" */
- struct epitem *base;
-
- /*
- * Wait queue item that will be linked to the target file wait
- * queue head.
- */
- wait_queue_entry_t wait;
-
- /* The wait queue head that linked the "wait" wait queue item */
- wait_queue_head_t *whead;
-};
-
/* Wrapper struct used by poll queueing */
struct ep_pqueue {
poll_table pt;
@@ -617,13 +617,11 @@ static void ep_remove_wait_queue(struct eppoll_entry *pwq)
*/
static void ep_unregister_pollwait(struct eventpoll *ep, struct epitem *epi)
{
- struct list_head *lsthead = &epi->pwqlist;
+ struct eppoll_entry **p = &epi->pwqlist;
struct eppoll_entry *pwq;

- while (!list_empty(lsthead)) {
- pwq = list_first_entry(lsthead, struct eppoll_entry, llink);
-
- list_del(&pwq->llink);
+ while ((pwq = *p) != NULL) {
+ *p = pwq->next;
ep_remove_wait_queue(pwq);
kmem_cache_free(pwq_cache, pwq);
}
@@ -1320,7 +1318,8 @@ static void ep_ptable_queue_proc(struct file *file, wait_queue_head_t *whead,
add_wait_queue_exclusive(whead, &pwq->wait);
else
add_wait_queue(whead, &pwq->wait);
- list_add_tail(&pwq->llink, &epi->pwqlist);
+ pwq->next = epi->pwqlist;
+ epi->pwqlist = pwq;
epi->nwait++;
} else {
/* We have to signal that an error occurred */
@@ -1507,7 +1506,7 @@ static int ep_insert(struct eventpoll *ep, const struct epoll_event *event,
/* Item initialization follow here ... */
INIT_LIST_HEAD(&epi->rdllink);
INIT_LIST_HEAD(&epi->fllink);
- INIT_LIST_HEAD(&epi->pwqlist);
+ epi->pwqlist = NULL;
epi->ep = ep;
ep_set_ffd(&epi->ffd, tfile, fd);
epi->event = *event;
--
2.11.0