io_uring/rw: add iovec recycling

Let the io_async_rw hold on to the iovec and reuse it, rather than always
allocate and free them.

Also enables KASAN for the iovec entries, so that reuse can be detected
even while they are in the cache.

While doing so, shrink io_async_rw by getting rid of the bigger embedded
fast iovec. Since iovecs are being recycled now, shrink it from 8 to 1.
This reduces the io_async_rw size from 264 to 160 bytes, a 40% reduction.

Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 2 insertions, 1 deletions

diff --git a/io_uring/rw.h b/io_uring/rw.h
index 7824896dc52d..cf51d0eb407a 100644
--- a/io_uring/rw.h
+++ b/io_uring/rw.h
@@ -9,8 +9,9 @@ struct io_async_rw {
 	};
 	struct iov_iter			iter;
 	struct iov_iter_state		iter_state;
-	struct iovec			fast_iov[UIO_FASTIOV];
+	struct iovec			fast_iov;
 	struct iovec			*free_iovec;
+	int				free_iov_nr;
 	struct wait_page_queue		wpq;
 };