io_uring: make poll->wait dynamically allocated

In the quest to bring io_kiocb down to 3 cachelines, this one does
the trick. Make the wait_queue_entry for the poll command come out
of kmalloc instead of embedding it in struct io_poll_iocb, as the
latter is the largest member of io_kiocb. Once we trim this down a
bit, we're back at a healthy 192 bytes for struct io_kiocb.

Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/fs/io_uring.c b/fs/io_uring.c
index e44b0e01f1b5710c9641a17cf6721a7c0e599049..2c2e8c25da01b57aee1570708ef159fc36d5982d 100644 (file)
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -291,7 +291,7 @@ struct io_poll_iocb {
        __poll_t                        events;
        bool                            done;
        bool                            canceled;
-       struct wait_queue_entry         wait;
+       struct wait_queue_entry         *wait;
 };
 
 struct io_timeout_data {
@@ -2030,8 +2030,8 @@ static void io_poll_remove_one(struct io_kiocb *req)
 
        spin_lock(&poll->head->lock);
        WRITE_ONCE(poll->canceled, true);
-       if (!list_empty(&poll->wait.entry)) {
-               list_del_init(&poll->wait.entry);
+       if (!list_empty(&poll->wait->entry)) {
+               list_del_init(&poll->wait->entry);
                io_queue_async_work(req);
        }
        spin_unlock(&poll->head->lock);
@@ -2104,6 +2104,7 @@ static void io_poll_complete(struct io_kiocb *req, __poll_t mask, int error)
        struct io_ring_ctx *ctx = req->ctx;
 
        req->poll.done = true;
+       kfree(req->poll.wait);
        if (error)
                io_cqring_fill_event(req, error);
        else
@@ -2141,7 +2142,7 @@ static void io_poll_complete_work(struct io_wq_work **workptr)
         */
        spin_lock_irq(&ctx->completion_lock);
        if (!mask && ret != -ECANCELED) {
-               add_wait_queue(poll->head, &poll->wait);
+               add_wait_queue(poll->head, poll->wait);
                spin_unlock_irq(&ctx->completion_lock);
                return;
        }
@@ -2161,8 +2162,7 @@ static void io_poll_complete_work(struct io_wq_work **workptr)
 static int io_poll_wake(struct wait_queue_entry *wait, unsigned mode, int sync,
                        void *key)
 {
-       struct io_poll_iocb *poll = container_of(wait, struct io_poll_iocb,
-                                                       wait);
+       struct io_poll_iocb *poll = wait->private;
        struct io_kiocb *req = container_of(poll, struct io_kiocb, poll);
        struct io_ring_ctx *ctx = req->ctx;
        __poll_t mask = key_to_poll(key);
@@ -2172,7 +2172,7 @@ static int io_poll_wake(struct wait_queue_entry *wait, unsigned mode, int sync,
        if (mask && !(mask & poll->events))
                return 0;
 
-       list_del_init(&poll->wait.entry);
+       list_del_init(&poll->wait->entry);
 
        /*
         * Run completion inline if we can. We're using trylock here because
@@ -2213,7 +2213,7 @@ static void io_poll_queue_proc(struct file *file, struct wait_queue_head *head,
 
        pt->error = 0;
        pt->req->poll.head = head;
-       add_wait_queue(head, &pt->req->poll.wait);
+       add_wait_queue(head, pt->req->poll.wait);
 }
 
 static void io_poll_req_insert(struct io_kiocb *req)
@@ -2252,6 +2252,10 @@ static int io_poll_add(struct io_kiocb *req, const struct io_uring_sqe *sqe,
        if (!poll->file)
                return -EBADF;
 
+       poll->wait = kmalloc(sizeof(*poll->wait), GFP_KERNEL);
+       if (!poll->wait)
+               return -ENOMEM;
+
        req->sqe = NULL;
        INIT_IO_WORK(&req->work, io_poll_complete_work);
        events = READ_ONCE(sqe->poll_events);
@@ -2268,8 +2272,9 @@ static int io_poll_add(struct io_kiocb *req, const struct io_uring_sqe *sqe,
        ipt.error = -EINVAL; /* same as no support for IOCB_CMD_POLL */
 
        /* initialized the list so that we can do list_empty checks */
-       INIT_LIST_HEAD(&poll->wait.entry);
-       init_waitqueue_func_entry(&poll->wait, io_poll_wake);
+       INIT_LIST_HEAD(&poll->wait->entry);
+       init_waitqueue_func_entry(poll->wait, io_poll_wake);
+       poll->wait->private = poll;
 
        INIT_LIST_HEAD(&req->list);
 
@@ -2278,14 +2283,14 @@ static int io_poll_add(struct io_kiocb *req, const struct io_uring_sqe *sqe,
        spin_lock_irq(&ctx->completion_lock);
        if (likely(poll->head)) {
                spin_lock(&poll->head->lock);
-               if (unlikely(list_empty(&poll->wait.entry))) {
+               if (unlikely(list_empty(&poll->wait->entry))) {
                        if (ipt.error)
                                cancel = true;
                        ipt.error = 0;
                        mask = 0;
                }
                if (mask || ipt.error)
-                       list_del_init(&poll->wait.entry);
+                       list_del_init(&poll->wait->entry);
                else if (cancel)
                        WRITE_ONCE(poll->canceled, true);
                else if (!poll->done) /* actually waiting for an event */