diff mbox series

[15/15] io_uring: add io_uring_event cache hit information

Message ID 20190110024404.25372-16-axboe@kernel.dk (mailing list archive)
State New, archived
Headers show
Series [01/15] fs: add an iopoll method to struct file_operations | expand

Commit Message

Jens Axboe Jan. 10, 2019, 2:44 a.m. UTC
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 <axboe@kernel.dk>
---
 fs/io_uring.c                 | 7 ++++++-
 include/uapi/linux/io_uring.h | 5 +++++
 2 files changed, 11 insertions(+), 1 deletion(-)

Comments

Jeff Moyer Jan. 10, 2019, 11:12 p.m. UTC | #1
Jens Axboe <axboe@kernel.dk> writes:

> 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.

We may want to hold off on this one until the whole mincore/RWF_NOWAIT
debate is sorted. [1]

Cheers,
Jeff

[1] https://lore.kernel.org/lkml/20190109022430.GE27534@dastard/
Jens Axboe Jan. 10, 2019, 11:47 p.m. UTC | #2
On 1/10/19 4:12 PM, Jeff Moyer wrote:
> Jens Axboe <axboe@kernel.dk> writes:
> 
>> 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.
> 
> We may want to hold off on this one until the whole mincore/RWF_NOWAIT
> debate is sorted. [1]

Definitely, it's why it's separate and at the end of the series. But
in reality, this doesn't leak anything that timing doesn't already
tell you. So it's kind of a moot point.
diff mbox series

Patch

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 6c62329b00ec..f2a603c447ba 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -511,11 +511,16 @@  static void io_fill_cq_error(struct io_ring_ctx *ctx, struct sqe_submit *s,
 static void io_complete_scqring_rw(struct kiocb *kiocb, long res, long res2)
 {
 	struct io_kiocb *iocb = container_of(kiocb, struct io_kiocb, rw);
+	unsigned ev_flags = 0;
 
 	kiocb_end_write(kiocb);
 
 	fput(kiocb->ki_filp);
-	io_cqring_fill_event(iocb->ki_ctx, iocb->ki_index, res, 0);
+
+	if (res > 0 && test_bit(KIOCB_F_FORCE_NONBLOCK, &iocb->ki_flags))
+		ev_flags = IOCQE_FLAG_CACHEHIT;
+
+	io_cqring_fill_event(iocb->ki_ctx, iocb->ki_index, res, ev_flags);
 	io_free_kiocb(iocb);
 }
 
diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index 9321eb97479d..20e4c22e040d 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -55,6 +55,11 @@  struct io_uring_cqe {
 	__u32	flags;
 };
 
+/*
+ * io_uring_event->flags
+ */
+#define IOCQE_FLAG_CACHEHIT	(1 << 0)	/* IO did not hit media */
+
 /*
  * Magic offsets for the application to mmap the data it needs
  */