linux-kernel - [PATCH 2/2] io_uring: batch put_task

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Date:   Sat, 18 Jul 2020 11:32:52 +0300
From:   Pavel Begunkov <asml.silence@...il.com>
To:     Jens Axboe <axboe@...nel.dk>, io-uring@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH 2/2] io_uring: batch put_task_struct()

As every iopoll request have a task ref, it becomes expensive to put
them one by one, instead we can put several at once integrating that
into io_req_free_batch().

Signed-off-by: Pavel Begunkov <asml.silence@...il.com>
---
 fs/io_uring.c | 28 ++++++++++++++++++++++++++--
 1 file changed, 26 insertions(+), 2 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 57e1f26b6a6b..b52aa0d8b09d 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -1543,7 +1543,6 @@ static void io_dismantle_req(struct io_kiocb *req)
 		kfree(req->io);
 	if (req->file)
 		io_put_file(req, req->file, (req->flags & REQ_F_FIXED_FILE));
-	__io_put_req_task(req);
 	io_req_clean_work(req);
 
 	if (req->flags & REQ_F_INFLIGHT) {
@@ -1563,6 +1562,7 @@ static void __io_free_req(struct io_kiocb *req)
 	struct io_ring_ctx *ctx;
 
 	io_dismantle_req(req);
+	__io_put_req_task(req);
 	ctx = req->ctx;
 	if (likely(!io_is_fallback_req(req)))
 		kmem_cache_free(req_cachep, req);
@@ -1806,8 +1806,18 @@ static void io_free_req(struct io_kiocb *req)
 struct req_batch {
 	void *reqs[IO_IOPOLL_BATCH];
 	int to_free;
+
+	struct task_struct	*task;
+	int			task_refs;
 };
 
+static inline void io_init_req_batch(struct req_batch *rb)
+{
+	rb->to_free = 0;
+	rb->task_refs = 0;
+	rb->task = NULL;
+}
+
 static void __io_req_free_batch_flush(struct io_ring_ctx *ctx,
 				      struct req_batch *rb)
 {
@@ -1821,6 +1831,10 @@ static void io_req_free_batch_finish(struct io_ring_ctx *ctx,
 {
 	if (rb->to_free)
 		__io_req_free_batch_flush(ctx, rb);
+	if (rb->task) {
+		put_task_struct_many(rb->task, rb->task_refs);
+		rb->task = NULL;
+	}
 }
 
 static void io_req_free_batch(struct req_batch *rb, struct io_kiocb *req)
@@ -1832,6 +1846,16 @@ static void io_req_free_batch(struct req_batch *rb, struct io_kiocb *req)
 	if (req->flags & REQ_F_LINK_HEAD)
 		io_queue_next(req);
 
+	if (req->flags & REQ_F_TASK_PINNED) {
+		if (req->task != rb->task && rb->task) {
+			put_task_struct_many(rb->task, rb->task_refs);
+			rb->task = req->task;
+			rb->task_refs = 0;
+		}
+		rb->task_refs++;
+		req->flags &= ~REQ_F_TASK_PINNED;
+	}
+
 	io_dismantle_req(req);
 	rb->reqs[rb->to_free++] = req;
 	if (unlikely(rb->to_free == ARRAY_SIZE(rb->reqs)))
@@ -1977,7 +2001,7 @@ static void io_iopoll_complete(struct io_ring_ctx *ctx, unsigned int *nr_events,
 	/* order with ->result store in io_complete_rw_iopoll() */
 	smp_rmb();
 
-	rb.to_free = 0;
+	io_init_req_batch(&rb);
 	while (!list_empty(done)) {
 		int cflags = 0;
 
-- 
2.24.0