io_uring: use slist for completion batching

Currently we collect requests for completion batching in an array.
Replace them with a singly linked list. It's as fast as arrays but
doesn't take some much space in ctx, and will be used in future patches.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/a666826f2854d17e9fb9417fb302edfeb750f425.1632516769.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 27ca4fb733f96c80ba61434a894187c61b35eb52..0ccfd70af3e0d88353ff8f7f25f5590fa0c1df5b 100644 (file)
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -322,8 +322,8 @@ struct io_submit_state {
        /*
         * Batch completion logic
         */
-       struct io_kiocb         *compl_reqs[IO_COMPL_BATCH];
-       unsigned int            compl_nr;
+       struct io_wq_work_list  compl_reqs;
+
        /* inline/task_work completion list, under ->uring_lock */
        struct list_head        free_list;
 };
@@ -882,6 +882,8 @@ struct io_kiocb {
        struct io_wq_work               work;
        const struct cred               *creds;
 
+       struct io_wq_work_node          comp_list;
+
        /* store used ubuf, so we can prevent reloading */
        struct io_mapped_ubuf           *imu;
 };
@@ -1168,7 +1170,7 @@ static inline void req_ref_get(struct io_kiocb *req)
 
 static inline void io_submit_flush_completions(struct io_ring_ctx *ctx)
 {
-       if (ctx->submit_state.compl_nr)
+       if (!wq_list_empty(&ctx->submit_state.compl_reqs))
                __io_submit_flush_completions(ctx);
 }
 
@@ -1325,6 +1327,7 @@ static struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p)
        INIT_LIST_HEAD(&ctx->submit_state.free_list);
        INIT_LIST_HEAD(&ctx->locked_free_list);
        INIT_DELAYED_WORK(&ctx->fallback_work, io_fallback_req_func);
+       INIT_WQ_LIST(&ctx->submit_state.compl_reqs);
        return ctx;
 err:
        kfree(ctx->dummy_ubuf);
@@ -1826,11 +1829,16 @@ static inline bool io_req_needs_clean(struct io_kiocb *req)
 static void io_req_complete_state(struct io_kiocb *req, long res,
                                  unsigned int cflags)
 {
+       struct io_submit_state *state;
+
        if (io_req_needs_clean(req))
                io_clean_op(req);
        req->result = res;
        req->compl.cflags = cflags;
        req->flags |= REQ_F_COMPLETE_INLINE;
+
+       state = &req->ctx->submit_state;
+       wq_list_add_tail(&req->comp_list, &state->compl_reqs);
 }
 
 static inline void __io_req_complete(struct io_kiocb *req, unsigned issue_flags,
@@ -2319,13 +2327,14 @@ static void io_req_free_batch(struct req_batch *rb, struct io_kiocb *req,
 static void __io_submit_flush_completions(struct io_ring_ctx *ctx)
        __must_hold(&ctx->uring_lock)
 {
+       struct io_wq_work_node *node, *prev;
        struct io_submit_state *state = &ctx->submit_state;
-       int i, nr = state->compl_nr;
        struct req_batch rb;
 
        spin_lock(&ctx->completion_lock);
-       for (i = 0; i < nr; i++) {
-               struct io_kiocb *req = state->compl_reqs[i];
+       wq_list_for_each(node, prev, &state->compl_reqs) {
+               struct io_kiocb *req = container_of(node, struct io_kiocb,
+                                                   comp_list);
 
                __io_cqring_fill_event(ctx, req->user_data, req->result,
                                        req->compl.cflags);
@@ -2335,15 +2344,18 @@ static void __io_submit_flush_completions(struct io_ring_ctx *ctx)
        io_cqring_ev_posted(ctx);
 
        io_init_req_batch(&rb);
-       for (i = 0; i < nr; i++) {
-               struct io_kiocb *req = state->compl_reqs[i];
+       node = state->compl_reqs.first;
+       do {
+               struct io_kiocb *req = container_of(node, struct io_kiocb,
+                                                   comp_list);
 
+               node = req->comp_list.next;
                if (req_ref_put_and_test(req))
                        io_req_free_batch(&rb, req, &ctx->submit_state);
-       }
+       } while (node);
 
        io_req_free_batch_finish(ctx, &rb);
-       state->compl_nr = 0;
+       INIT_WQ_LIST(&state->compl_reqs);
 }
 
 /*
@@ -2668,17 +2680,10 @@ static void io_req_task_complete(struct io_kiocb *req, bool *locked)
        unsigned int cflags = io_put_rw_kbuf(req);
        long res = req->result;
 
-       if (*locked) {
-               struct io_ring_ctx *ctx = req->ctx;
-               struct io_submit_state *state = &ctx->submit_state;
-
+       if (*locked)
                io_req_complete_state(req, res, cflags);
-               state->compl_reqs[state->compl_nr++] = req;
-               if (state->compl_nr == ARRAY_SIZE(state->compl_reqs))
-                       io_submit_flush_completions(ctx);
-       } else {
+       else
                io_req_complete_post(req, res, cflags);
-       }
 }
 
 static void __io_complete_rw(struct io_kiocb *req, long res, long res2,
@@ -6962,15 +6967,8 @@ issue_sqe:
         * doesn't support non-blocking read/write attempts
         */
        if (likely(!ret)) {
-               if (req->flags & REQ_F_COMPLETE_INLINE) {
-                       struct io_ring_ctx *ctx = req->ctx;
-                       struct io_submit_state *state = &ctx->submit_state;
-
-                       state->compl_reqs[state->compl_nr++] = req;
-                       if (state->compl_nr == ARRAY_SIZE(state->compl_reqs))
-                               io_submit_flush_completions(ctx);
+               if (req->flags & REQ_F_COMPLETE_INLINE)
                        return;
-               }
 
                linked_timeout = io_prep_linked_timeout(req);
                if (linked_timeout)