io_uring: optimise read/write iov state storing

Currently io_read() and io_write() keep separate pointers to an iter and
to struct iov_iter_state, which is not great for register spilling and
requires more on-stack copies. They are both either on-stack or in
req->async_data at the same time, so use struct io_rw_state and keep a
pointer only to it, so having all the state with just one pointer.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/5c5e7ffd7dc25fc35075c70411ba99df72f237fa.1634144845.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 4736561..bb5cd87 100644 (file)
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -695,9 +695,9 @@ struct io_async_msghdr {
 };
 
 struct io_rw_state {
-       struct iovec                    fast_iov[UIO_FASTIOV];
        struct iov_iter                 iter;
        struct iov_iter_state           iter_state;
+       struct iovec                    fast_iov[UIO_FASTIOV];
 };
 
 struct io_async_rw {
@@ -3297,8 +3297,7 @@ static inline bool io_alloc_async_data(struct io_kiocb *req)
 }
 
 static int io_setup_async_rw(struct io_kiocb *req, const struct iovec *iovec,
-                            const struct iovec *fast_iov,
-                            struct iov_iter *iter, bool force)
+                            struct io_rw_state *s, bool force)
 {
        if (!force && !io_op_defs[req->opcode].needs_async_setup)
                return 0;
@@ -3310,7 +3309,7 @@ static int io_setup_async_rw(struct io_kiocb *req, const struct iovec *iovec,
                        return -ENOMEM;
                }
 
-               io_req_map_rw(req, iovec, fast_iov, iter);
+               io_req_map_rw(req, iovec, s->fast_iov, &s->iter);
                iorw = req->async_data;
                /* we've copied and mapped the iter, ensure state is saved */
                iov_iter_save_state(&iorw->s.iter, &iorw->s.iter_state);
@@ -3432,33 +3431,33 @@ static bool need_read_all(struct io_kiocb *req)
 
 static int io_read(struct io_kiocb *req, unsigned int issue_flags)
 {
-       struct iovec inline_vecs[UIO_FASTIOV], *iovec = inline_vecs;
+       struct io_rw_state __s, *s;
+       struct iovec *iovec;
        struct kiocb *kiocb = &req->rw.kiocb;
-       struct iov_iter __iter, *iter = &__iter;
        bool force_nonblock = issue_flags & IO_URING_F_NONBLOCK;
-       struct iov_iter_state __state, *state;
        struct io_async_rw *rw;
        ssize_t ret, ret2;
 
        if (req_has_async_data(req)) {
                rw = req->async_data;
-               iter = &rw->s.iter;
-               state = &rw->s.iter_state;
+               s = &rw->s;
                /*
                 * We come here from an earlier attempt, restore our state to
                 * match in case it doesn't. It's cheap enough that we don't
                 * need to make this conditional.
                 */
-               iov_iter_restore(iter, state);
+               iov_iter_restore(&s->iter, &s->iter_state);
                iovec = NULL;
        } else {
-               ret = io_import_iovec(READ, req, &iovec, iter, !force_nonblock);
+               s = &__s;
+               iovec = s->fast_iov;
+               ret = io_import_iovec(READ, req, &iovec, &s->iter, !force_nonblock);
                if (ret < 0)
                        return ret;
-               state = &__state;
-               iov_iter_save_state(iter, state);
+
+               iov_iter_save_state(&s->iter, &s->iter_state);
        }
-       req->result = iov_iter_count(iter);
+       req->result = iov_iter_count(&s->iter);
 
        /* Ensure we clear previously set non-block flag */
        if (!force_nonblock)
@@ -3468,7 +3467,7 @@ static int io_read(struct io_kiocb *req, unsigned int issue_flags)
 
        /* If the file doesn't support async, just async punt */
        if (force_nonblock && !io_file_supports_nowait(req, READ)) {
-               ret = io_setup_async_rw(req, iovec, inline_vecs, iter, true);
+               ret = io_setup_async_rw(req, iovec, s, true);
                return ret ?: -EAGAIN;
        }
 
@@ -3478,7 +3477,7 @@ static int io_read(struct io_kiocb *req, unsigned int issue_flags)
                return ret;
        }
 
-       ret = io_iter_do_read(req, iter);
+       ret = io_iter_do_read(req, &s->iter);
 
        if (ret == -EAGAIN || (req->flags & REQ_F_REISSUE)) {
                req->flags &= ~REQ_F_REISSUE;
@@ -3502,22 +3501,19 @@ static int io_read(struct io_kiocb *req, unsigned int issue_flags)
         * untouched in case of error. Restore it and we'll advance it
         * manually if we need to.
         */
-       iov_iter_restore(iter, state);
+       iov_iter_restore(&s->iter, &s->iter_state);
 
-       ret2 = io_setup_async_rw(req, iovec, inline_vecs, iter, true);
+       ret2 = io_setup_async_rw(req, iovec, s, true);
        if (ret2)
                return ret2;
 
        iovec = NULL;
        rw = req->async_data;
+       s = &rw->s;
        /*
         * Now use our persistent iterator and state, if we aren't already.
         * We've restored and mapped the iter to match.
         */
-       if (iter != &rw->s.iter) {
-               iter = &rw->s.iter;
-               state = &rw->s.iter_state;
-       }
 
        do {
                /*
@@ -3525,11 +3521,11 @@ static int io_read(struct io_kiocb *req, unsigned int issue_flags)
                 * above or inside this loop. Advance the iter by the bytes
                 * that were consumed.
                 */
-               iov_iter_advance(iter, ret);
-               if (!iov_iter_count(iter))
+               iov_iter_advance(&s->iter, ret);
+               if (!iov_iter_count(&s->iter))
                        break;
                rw->bytes_done += ret;
-               iov_iter_save_state(iter, state);
+               iov_iter_save_state(&s->iter, &s->iter_state);
 
                /* if we can retry, do so with the callbacks armed */
                if (!io_rw_should_retry(req)) {
@@ -3543,12 +3539,12 @@ static int io_read(struct io_kiocb *req, unsigned int issue_flags)
                 * desired page gets unlocked. We can also get a partial read
                 * here, and if we do, then just retry at the new offset.
                 */
-               ret = io_iter_do_read(req, iter);
+               ret = io_iter_do_read(req, &s->iter);
                if (ret == -EIOCBQUEUED)
                        return 0;
                /* we got some bytes, but not all. retry. */
                kiocb->ki_flags &= ~IOCB_WAITQ;
-               iov_iter_restore(iter, state);
+               iov_iter_restore(&s->iter, &s->iter_state);
        } while (ret > 0);
 done:
        kiocb_done(kiocb, ret, issue_flags);
@@ -3568,28 +3564,27 @@ static int io_write_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 
 static int io_write(struct io_kiocb *req, unsigned int issue_flags)
 {
-       struct iovec inline_vecs[UIO_FASTIOV], *iovec = inline_vecs;
+       struct io_rw_state __s, *s;
+       struct io_async_rw *rw;
+       struct iovec *iovec;
        struct kiocb *kiocb = &req->rw.kiocb;
-       struct iov_iter __iter, *iter = &__iter;
        bool force_nonblock = issue_flags & IO_URING_F_NONBLOCK;
-       struct iov_iter_state __state, *state;
-       struct io_async_rw *rw;
        ssize_t ret, ret2;
 
        if (req_has_async_data(req)) {
                rw = req->async_data;
-               iter = &rw->s.iter;
-               state = &rw->s.iter_state;
-               iov_iter_restore(iter, state);
+               s = &rw->s;
+               iov_iter_restore(&s->iter, &s->iter_state);
                iovec = NULL;
        } else {
-               ret = io_import_iovec(WRITE, req, &iovec, iter, !force_nonblock);
+               s = &__s;
+               iovec = s->fast_iov;
+               ret = io_import_iovec(WRITE, req, &iovec, &s->iter, !force_nonblock);
                if (ret < 0)
                        return ret;
-               state = &__state;
-               iov_iter_save_state(iter, state);
+               iov_iter_save_state(&s->iter, &s->iter_state);
        }
-       req->result = iov_iter_count(iter);
+       req->result = iov_iter_count(&s->iter);
 
        /* Ensure we clear previously set non-block flag */
        if (!force_nonblock)
@@ -3625,9 +3620,9 @@ static int io_write(struct io_kiocb *req, unsigned int issue_flags)
        kiocb->ki_flags |= IOCB_WRITE;
 
        if (req->file->f_op->write_iter)
-               ret2 = call_write_iter(req->file, kiocb, iter);
+               ret2 = call_write_iter(req->file, kiocb, &s->iter);
        else if (req->file->f_op->write)
-               ret2 = loop_rw_iter(WRITE, req, iter);
+               ret2 = loop_rw_iter(WRITE, req, &s->iter);
        else
                ret2 = -EINVAL;
 
@@ -3653,8 +3648,8 @@ done:
                kiocb_done(kiocb, ret2, issue_flags);
        } else {
 copy_iov:
-               iov_iter_restore(iter, state);
-               ret = io_setup_async_rw(req, iovec, inline_vecs, iter, false);
+               iov_iter_restore(&s->iter, &s->iter_state);
+               ret = io_setup_async_rw(req, iovec, s, false);
                return ret ?: -EAGAIN;
        }
 out_free: