On 11.09.19 г. 19:15 ч., Jens Axboe wrote:
> We currently merge async work items if we see a strict sequential hit.
> This helps avoid unnecessary workqueue switches when we don't need
> them. We can extend this merging to cover cases where it's not a strict
> sequential hit, but the IO still fits within the same page. If an
> application is doing multiple requests within the same page, we don't
> want separate workers waiting on the same page to complete IO. It's much
> faster to let the first worker bring in the page, then operate on that
> page from the same worker to complete the next request(s).
>
> Signed-off-by: Jens Axboe <ax...@kernel.dk>
>
> ---
>
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index 03fcd974fd1d..4bc3ee4ea81f 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -167,7 +167,7 @@ struct async_list {
> struct list_head list;
>
> struct file *file;
> - off_t io_end;
> + off_t io_start;
> size_t io_len;
> };
>
> @@ -1189,6 +1189,28 @@ static ssize_t io_import_iovec(struct io_ring_ctx
> *ctx, int rw,
> return import_iovec(rw, buf, sqe_len, UIO_FASTIOV, iovec, iter);
> }
>
> +static inline bool io_should_merge(struct async_list *al, struct kiocb
> *kiocb)
> +{
> + if (al->file == kiocb->ki_filp) {
> + off_t start, end;
> +
> + /*
> + * Allow merging if we're anywhere in the range of the same
> + * page. Generally this happens for sub-page reads or writes,
> + * and it's beneficial to allow the first worker to bring the
> + * page in and the piggy backed work can then work on the
> + * cached page.
> + */
> + start = al->io_start & PAGE_MASK;
nit: round_down(al->io_start, PAGE_SIZE);
> + end = (al->io_start + al->io_len + PAGE_SIZE - 1) & PAGE_MASK;
nit: round_up(al->io_start+io_len, PAGE_SIZE)
> + if (kiocb->ki_pos >= start && kiocb->ki_pos <= end)
> + return true;
> + }
> +
> + al->file = NULL;
> + return false;
> +}
> +
> /*
> * Make a note of the last file/offset/direction we punted to async
> * context. We'll use this information to see if we can piggy back a
> @@ -1200,9 +1222,8 @@ static void io_async_list_note(int rw, struct io_kiocb
> *req, size_t len)
> struct async_list *async_list = &req->ctx->pending_async[rw];
> struct kiocb *kiocb = &req->rw;
> struct file *filp = kiocb->ki_filp;
> - off_t io_end = kiocb->ki_pos + len;
>
> - if (filp == async_list->file && kiocb->ki_pos == async_list->io_end) {
> + if (io_should_merge(async_list, kiocb)) {
> unsigned long max_bytes;
>
> /* Use 8x RA size as a decent limiter for both reads/writes */
> @@ -1215,17 +1236,16 @@ static void io_async_list_note(int rw, struct
> io_kiocb *req, size_t len)
> req->flags |= REQ_F_SEQ_PREV;
> async_list->io_len += len;
> } else {
> - io_end = 0;
> - async_list->io_len = 0;
> + async_list->file = NULL;
> }
> }
>
> /* New file? Reset state. */
> if (async_list->file != filp) {
> - async_list->io_len = 0;
> + async_list->io_start = kiocb->ki_pos;
> + async_list->io_len = len;
> async_list->file = filp;
> }
> - async_list->io_end = io_end;
> }
>
> static int io_read(struct io_kiocb *req, const struct sqe_submit *s,
> @@ -1994,7 +2014,7 @@ static void io_sq_wq_submit_work(struct work_struct
> *work)
> */
> static bool io_add_to_prev_work(struct async_list *list, struct io_kiocb
> *req)
> {
> - bool ret = false;
> + bool ret;
>
> if (!list)
> return false;
>
