| Message ID | 20200618144355.17324-16-axboe@kernel.dk (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [01/15] block: provide plug based way of signaling forced no-wait semantics | expand |
On 18/06/2020 17:43, Jens Axboe wrote: > If the file is flagged with FMODE_BUF_RASYNC, then we don't have to punt > the buffered read to an io-wq worker. Instead we can rely on page > unlocking callbacks to support retry based async IO. This is a lot more > efficient than doing async thread offload. > > The retry is done similarly to how we handle poll based retry. From > the unlock callback, we simply queue the retry to a task_work based > handler. > > Signed-off-by: Jens Axboe <axboe@kernel.dk> > --- > fs/io_uring.c | 145 +++++++++++++++++++++++++++++++++++++++++++++++--- > 1 file changed, 137 insertions(+), 8 deletions(-) > ... > static int io_read(struct io_kiocb *req, bool force_nonblock) > { > struct iovec inline_vecs[UIO_FASTIOV], *iovec = inline_vecs; > @@ -2784,10 +2907,7 @@ static int io_read(struct io_kiocb *req, bool force_nonblock) > unsigned long nr_segs = iter.nr_segs; > ssize_t ret2 = 0; > > - if (req->file->f_op->read_iter) > - ret2 = call_read_iter(req->file, kiocb, &iter); > - else > - ret2 = loop_rw_iter(READ, req->file, kiocb, &iter); > + ret2 = io_iter_do_read(req, &iter); > > /* Catch -EAGAIN return for forced non-blocking submission */ > if (!force_nonblock || (ret2 != -EAGAIN && ret2 != -EIO)) { > @@ -2799,17 +2919,26 @@ static int io_read(struct io_kiocb *req, bool force_nonblock) > ret = io_setup_async_rw(req, io_size, iovec, > inline_vecs, &iter); > if (ret) > - goto out_free; > + goto out; > /* any defer here is final, must blocking retry */ > if (!(req->flags & REQ_F_NOWAIT) && > !file_can_poll(req->file)) > req->flags |= REQ_F_MUST_PUNT; > + /* if we can retry, do so with the callbacks armed */ > + if (io_rw_should_retry(req)) { > + ret2 = io_iter_do_read(req, &iter); > + if (ret2 == -EIOCBQUEUED) { > + goto out; > + } else if (ret2 != -EAGAIN) { > + kiocb_done(kiocb, ret2); > + goto out; > + } > + } > + kiocb->ki_flags &= ~IOCB_WAITQ; > return -EAGAIN; > } > } > -out_free: > - kfree(iovec); > - req->flags &= ~REQ_F_NEED_CLEANUP; This looks fishy. For instance, if it fails early on rw_verify_area(), how would it free yet on-stack iovec? Is it handled somehow? > +out: > return ret; > } > >
On 6/23/20 6:39 AM, Pavel Begunkov wrote: > On 18/06/2020 17:43, Jens Axboe wrote: >> If the file is flagged with FMODE_BUF_RASYNC, then we don't have to punt >> the buffered read to an io-wq worker. Instead we can rely on page >> unlocking callbacks to support retry based async IO. This is a lot more >> efficient than doing async thread offload. >> >> The retry is done similarly to how we handle poll based retry. From >> the unlock callback, we simply queue the retry to a task_work based >> handler. >> >> Signed-off-by: Jens Axboe <axboe@kernel.dk> >> --- >> fs/io_uring.c | 145 +++++++++++++++++++++++++++++++++++++++++++++++--- >> 1 file changed, 137 insertions(+), 8 deletions(-) >> > ... >> static int io_read(struct io_kiocb *req, bool force_nonblock) >> { >> struct iovec inline_vecs[UIO_FASTIOV], *iovec = inline_vecs; >> @@ -2784,10 +2907,7 @@ static int io_read(struct io_kiocb *req, bool force_nonblock) >> unsigned long nr_segs = iter.nr_segs; >> ssize_t ret2 = 0; >> >> - if (req->file->f_op->read_iter) >> - ret2 = call_read_iter(req->file, kiocb, &iter); >> - else >> - ret2 = loop_rw_iter(READ, req->file, kiocb, &iter); >> + ret2 = io_iter_do_read(req, &iter); >> >> /* Catch -EAGAIN return for forced non-blocking submission */ >> if (!force_nonblock || (ret2 != -EAGAIN && ret2 != -EIO)) { >> @@ -2799,17 +2919,26 @@ static int io_read(struct io_kiocb *req, bool force_nonblock) >> ret = io_setup_async_rw(req, io_size, iovec, >> inline_vecs, &iter); >> if (ret) >> - goto out_free; >> + goto out; >> /* any defer here is final, must blocking retry */ >> if (!(req->flags & REQ_F_NOWAIT) && >> !file_can_poll(req->file)) >> req->flags |= REQ_F_MUST_PUNT; >> + /* if we can retry, do so with the callbacks armed */ >> + if (io_rw_should_retry(req)) { >> + ret2 = io_iter_do_read(req, &iter); >> + if (ret2 == -EIOCBQUEUED) { >> + goto out; >> + } else if (ret2 != -EAGAIN) { >> + kiocb_done(kiocb, ret2); >> + goto out; >> + } >> + } >> + kiocb->ki_flags &= ~IOCB_WAITQ; >> return -EAGAIN; >> } >> } >> -out_free: >> - kfree(iovec); >> - req->flags &= ~REQ_F_NEED_CLEANUP; > > This looks fishy. For instance, if it fails early on rw_verify_area(), how would > it free yet on-stack iovec? Is it handled somehow? This was tweaked and rebased on top of the REQ_F_NEED_CLEANUP change, it should be correct in the tree: https://git.kernel.dk/cgit/linux-block/tree/fs/io_uring.c?h=for-5.9/io_uring#n2908
diff --git a/fs/io_uring.c b/fs/io_uring.c index 40413fb9d07b..94282be1c413 100644 --- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -78,6 +78,7 @@ #include <linux/fs_struct.h> #include <linux/splice.h> #include <linux/task_work.h> +#include <linux/pagemap.h> #define CREATE_TRACE_POINTS #include <trace/events/io_uring.h> @@ -503,6 +504,8 @@ struct io_async_rw { struct iovec *iov; ssize_t nr_segs; ssize_t size; + struct wait_page_queue wpq; + struct callback_head task_work; }; struct io_async_ctx { @@ -2750,6 +2753,126 @@ static int io_read_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe, return 0; } +static void __io_async_buf_error(struct io_kiocb *req, int error) +{ + struct io_ring_ctx *ctx = req->ctx; + + spin_lock_irq(&ctx->completion_lock); + io_cqring_fill_event(req, error); + io_commit_cqring(ctx); + spin_unlock_irq(&ctx->completion_lock); + + io_cqring_ev_posted(ctx); + req_set_fail_links(req); + io_double_put_req(req); +} + +static void io_async_buf_cancel(struct callback_head *cb) +{ + struct io_async_rw *rw; + struct io_kiocb *req; + + rw = container_of(cb, struct io_async_rw, task_work); + req = rw->wpq.wait.private; + __io_async_buf_error(req, -ECANCELED); +} + +static void io_async_buf_retry(struct callback_head *cb) +{ + struct io_async_rw *rw; + struct io_ring_ctx *ctx; + struct io_kiocb *req; + + rw = container_of(cb, struct io_async_rw, task_work); + req = rw->wpq.wait.private; + ctx = req->ctx; + + __set_current_state(TASK_RUNNING); + if (!io_sq_thread_acquire_mm(ctx, req)) { + mutex_lock(&ctx->uring_lock); + __io_queue_sqe(req, NULL); + mutex_unlock(&ctx->uring_lock); + } else { + __io_async_buf_error(req, -EFAULT); + } +} + +static int io_async_buf_func(struct wait_queue_entry *wait, unsigned mode, + int sync, void *arg) +{ + struct wait_page_queue *wpq; + struct io_kiocb *req = wait->private; + struct io_async_rw *rw = &req->io->rw; + struct wait_page_key *key = arg; + struct task_struct *tsk; + int ret; + + wpq = container_of(wait, struct wait_page_queue, wait); + + ret = wake_page_match(wpq, key); + if (ret != 1) + return ret; + + list_del_init(&wait->entry); + + init_task_work(&rw->task_work, io_async_buf_retry); + /* submit ref gets dropped, acquire a new one */ + refcount_inc(&req->refs); + tsk = req->task; + ret = task_work_add(tsk, &rw->task_work, true); + if (unlikely(ret)) { + /* queue just for cancelation */ + init_task_work(&rw->task_work, io_async_buf_cancel); + tsk = io_wq_get_task(req->ctx->io_wq); + task_work_add(tsk, &rw->task_work, true); + } + wake_up_process(tsk); + return 1; +} + +static bool io_rw_should_retry(struct io_kiocb *req) +{ + struct kiocb *kiocb = &req->rw.kiocb; + int ret; + + /* never retry for NOWAIT, we just complete with -EAGAIN */ + if (req->flags & REQ_F_NOWAIT) + return false; + + /* already tried, or we're doing O_DIRECT */ + if (kiocb->ki_flags & (IOCB_DIRECT | IOCB_WAITQ)) + return false; + /* + * just use poll if we can, and don't attempt if the fs doesn't + * support callback based unlocks + */ + if (file_can_poll(req->file) || !(req->file->f_mode & FMODE_BUF_RASYNC)) + return false; + + /* + * If request type doesn't require req->io to defer in general, + * we need to allocate it here + */ + if (!req->io && __io_alloc_async_ctx(req)) + return false; + + ret = kiocb_wait_page_queue_init(kiocb, &req->io->rw.wpq, + io_async_buf_func, req); + if (!ret) { + io_get_req_task(req); + return true; + } + + return false; +} + +static int io_iter_do_read(struct io_kiocb *req, struct iov_iter *iter) +{ + if (req->file->f_op->read_iter) + return call_read_iter(req->file, &req->rw.kiocb, iter); + return loop_rw_iter(READ, req->file, &req->rw.kiocb, iter); +} + static int io_read(struct io_kiocb *req, bool force_nonblock) { struct iovec inline_vecs[UIO_FASTIOV], *iovec = inline_vecs; @@ -2784,10 +2907,7 @@ static int io_read(struct io_kiocb *req, bool force_nonblock) unsigned long nr_segs = iter.nr_segs; ssize_t ret2 = 0; - if (req->file->f_op->read_iter) - ret2 = call_read_iter(req->file, kiocb, &iter); - else - ret2 = loop_rw_iter(READ, req->file, kiocb, &iter); + ret2 = io_iter_do_read(req, &iter); /* Catch -EAGAIN return for forced non-blocking submission */ if (!force_nonblock || (ret2 != -EAGAIN && ret2 != -EIO)) { @@ -2799,17 +2919,26 @@ static int io_read(struct io_kiocb *req, bool force_nonblock) ret = io_setup_async_rw(req, io_size, iovec, inline_vecs, &iter); if (ret) - goto out_free; + goto out; /* any defer here is final, must blocking retry */ if (!(req->flags & REQ_F_NOWAIT) && !file_can_poll(req->file)) req->flags |= REQ_F_MUST_PUNT; + /* if we can retry, do so with the callbacks armed */ + if (io_rw_should_retry(req)) { + ret2 = io_iter_do_read(req, &iter); + if (ret2 == -EIOCBQUEUED) { + goto out; + } else if (ret2 != -EAGAIN) { + kiocb_done(kiocb, ret2); + goto out; + } + } + kiocb->ki_flags &= ~IOCB_WAITQ; return -EAGAIN; } } -out_free: - kfree(iovec); - req->flags &= ~REQ_F_NEED_CLEANUP; +out: return ret; }
If the file is flagged with FMODE_BUF_RASYNC, then we don't have to punt the buffered read to an io-wq worker. Instead we can rely on page unlocking callbacks to support retry based async IO. This is a lot more efficient than doing async thread offload. The retry is done similarly to how we handle poll based retry. From the unlock callback, we simply queue the retry to a task_work based handler. Signed-off-by: Jens Axboe <axboe@kernel.dk> --- fs/io_uring.c | 145 +++++++++++++++++++++++++++++++++++++++++++++++--- 1 file changed, 137 insertions(+), 8 deletions(-)