On 2/10/19 2:36 AM, Hannes Reinecke wrote: > On 2/9/19 10:13 PM, Jens Axboe wrote: >> Add hint on whether a read was served out of the page cache, or if it >> hit media. This is useful for buffered async IO, O_DIRECT reads would >> never have this set (for obvious reasons). >> >> If the read hit page cache, cqe->flags will have IOCQE_FLAG_CACHEHIT >> set. >> >> Signed-off-by: Jens Axboe <[email protected]> >> --- >> fs/io_uring.c | 7 ++++++- >> include/uapi/linux/io_uring.h | 5 +++++ >> 2 files changed, 11 insertions(+), 1 deletion(-) >> >> diff --git a/fs/io_uring.c b/fs/io_uring.c >> index 11a549b5dcbf..d7a10484d748 100644 >> --- a/fs/io_uring.c >> +++ b/fs/io_uring.c >> @@ -587,11 +587,16 @@ static void io_fput(struct io_kiocb *req) >> static void io_complete_rw(struct kiocb *kiocb, long res, long res2) >> { >> struct io_kiocb *req = container_of(kiocb, struct io_kiocb, rw); >> + unsigned ev_flags = 0; >> >> kiocb_end_write(kiocb); >> >> io_fput(req); >> - io_cqring_add_event(req->ctx, req->user_data, res, 0); >> + >> + if (res > 0 && (req->flags & REQ_F_FORCE_NONBLOCK)) >> + ev_flags = IOCQE_FLAG_CACHEHIT; >> + >> + io_cqring_add_event(req->ctx, req->user_data, res, ev_flags); >> io_free_req(req); >> } >> >> diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h >> index e23408692118..24906e99fdc7 100644 >> --- a/include/uapi/linux/io_uring.h >> +++ b/include/uapi/linux/io_uring.h >> @@ -69,6 +69,11 @@ struct io_uring_cqe { >> __u32 flags; >> }; >> >> +/* >> + * io_uring_event->flags >> + */ >> +#define IOCQE_FLAG_CACHEHIT (1U << 0) /* IO did not hit media */ >> + >> /* >> * Magic offsets for the application to mmap the data it needs >> */ >> > > Hmm. The point of this patch being ... what? > Just setting a newly introduced flag seems to be a bit pointless. > Unless it has some magic interaction with io_cqring_add_event(). > But then that function would have had to have knowledge of that flag > already, which would be ... odd.
Not sure I follow your concern here. The kernel doesn't use the flag, we just set it. It's used to inform the application of whether or not the given read was a cachehit, or if it had to be served by media. -- Jens Axboe
