aio: use iovec array rather than the single one

Previously, we only offer a single iovec to handle all the read/write cases, so
the PREADV/PWRITEV request always need to alloc more iovec buffer when copying
user vectors.
If we use a tmp iovec array rather than the single one, some small PREADV/PWRITEV
workloads(vector size small than the tmp buffer) will not need to alloc more
iovec buffer when copying user vectors.

Reviewed-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Gu Zheng <guz.fnst@cn.fujitsu.com>
Signed-off-by: Benjamin LaHaise <bcrl@kvack.org>

fs/aio.c

@@ -1243,12 +1243,12 @@ static ssize_t aio_setup_vectored_rw(struct kiocb *kiocb,
 	if (compat)
 		ret = compat_rw_copy_check_uvector(rw,
 				(struct compat_iovec __user *)buf,
-				*nr_segs, 1, *iovec, iovec);
+				*nr_segs, UIO_FASTIOV, *iovec, iovec);
 	else
 #endif
 		ret = rw_copy_check_uvector(rw,
 				(struct iovec __user *)buf,
-				*nr_segs, 1, *iovec, iovec);
+				*nr_segs, UIO_FASTIOV, *iovec, iovec);
 	if (ret < 0)
 		return ret;
 
@@ -1285,7 +1285,7 @@ static ssize_t aio_run_iocb(struct kiocb *req, unsigned opcode,
 	fmode_t mode;
 	aio_rw_op *rw_op;
 	rw_iter_op *iter_op;
-	struct iovec inline_vec, *iovec = &inline_vec;
+	struct iovec inline_vecs[UIO_FASTIOV], *iovec = inline_vecs;
 	struct iov_iter iter;
 
 	switch (opcode) {
@@ -1320,7 +1320,7 @@ rw_common:
 		if (!ret)
 			ret = rw_verify_area(rw, file, &req->ki_pos, req->ki_nbytes);
 		if (ret < 0) {
-			if (iovec != &inline_vec)
+			if (iovec != inline_vecs)
 				kfree(iovec);
 			return ret;
 		}
@@ -1367,7 +1367,7 @@ rw_common:
 		return -EINVAL;
 	}
 
-	if (iovec != &inline_vec)
+	if (iovec != inline_vecs)
 		kfree(iovec);
 
 	if (ret != -EIOCBQUEUED) {