io_uring: assign new io_identity for task if members have changed

This avoids doing a copy for each new async IO, if some parts of the
io_identity has changed. We avoid reference counting for the normal
fast path of nothing ever changing.

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

diff --git a/fs/io_uring.c b/fs/io_uring.c
index ae91632..7020c6a 100644 (file)
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -1066,12 +1066,18 @@ static void io_init_identity(struct io_identity *id)
  */
 static inline void io_req_init_async(struct io_kiocb *req)
 {
+       struct io_uring_task *tctx = current->io_uring;
+
        if (req->flags & REQ_F_WORK_INITIALIZED)
                return;
 
        memset(&req->work, 0, sizeof(req->work));
        req->flags |= REQ_F_WORK_INITIALIZED;
-       req->work.identity = &current->io_uring->identity;
+
+       /* Grab a ref if this isn't our static identity */
+       req->work.identity = tctx->identity;
+       if (tctx->identity != &tctx->__identity)
+               refcount_inc(&req->work.identity->count);
 }
 
 static inline bool io_async_submit(struct io_ring_ctx *ctx)
@@ -1179,7 +1185,7 @@ static void __io_commit_cqring(struct io_ring_ctx *ctx)
 
 static void io_put_identity(struct io_uring_task *tctx, struct io_kiocb *req)
 {
-       if (req->work.identity == &tctx->identity)
+       if (req->work.identity == &tctx->__identity)
                return;
        if (refcount_dec_and_test(&req->work.identity->count))
                kfree(req->work.identity);
@@ -1254,11 +1260,12 @@ static bool io_identity_cow(struct io_kiocb *req)
        refcount_inc(&id->count);
 
        /* drop old identity, assign new one. one ref for req, one for tctx */
-       if (req->work.identity != &tctx->identity &&
+       if (req->work.identity != tctx->identity &&
            refcount_sub_and_test(2, &req->work.identity->count))
                kfree(req->work.identity);
 
        req->work.identity = id;
+       tctx->identity = id;
        return true;
 }
 
@@ -7691,7 +7698,8 @@ static int io_uring_alloc_task_context(struct task_struct *task)
        tctx->in_idle = 0;
        atomic_long_set(&tctx->req_issue, 0);
        atomic_long_set(&tctx->req_complete, 0);
-       io_init_identity(&tctx->identity);
+       io_init_identity(&tctx->__identity);
+       tctx->identity = &tctx->__identity;
        task->io_uring = tctx;
        return 0;
 }
@@ -7701,6 +7709,9 @@ void __io_uring_free(struct task_struct *tsk)
        struct io_uring_task *tctx = tsk->io_uring;
 
        WARN_ON_ONCE(!xa_empty(&tctx->xa));
+       WARN_ON_ONCE(refcount_read(&tctx->identity->count) != 1);
+       if (tctx->identity != &tctx->__identity)
+               kfree(tctx->identity);
        kfree(tctx);
        tsk->io_uring = NULL;
 }

diff --git a/include/linux/io_uring.h b/include/linux/io_uring.h
index bd33461..607d14f 100644 (file)
--- a/include/linux/io_uring.h
+++ b/include/linux/io_uring.h
@@ -24,7 +24,8 @@ struct io_uring_task {
        struct wait_queue_head  wait;
        struct file             *last;
        atomic_long_t           req_issue;
-       struct io_identity      identity;
+       struct io_identity      __identity;
+       struct io_identity      *identity;
 
        /* completion side */
        bool                    in_idle ____cacheline_aligned_in_smp;