On 05/02/2021 07:17, Stefan Metzmacher wrote:
> Hi Pavel,
>
>> static int io_sendmsg_copy_hdr(struct io_kiocb *req,
>> struct io_async_msghdr *iomsg)
>> {
>> - iomsg->iov = iomsg->fast_iov;
>> iomsg->msg.msg_name = &iomsg->addr;
>> + iomsg->free_iov = iomsg->fast_iov;
>
> Why this? Isn't the idea of this patch that free_iov is never == fast_iov?
That's a part of __import_iovec() and sendmsg_copy_msghdr() API, you pass
fast_iov as such and get back NULL or a newly allocated one in it.
>
>
>> @@ -4704,10 +4703,11 @@ static int __io_recvmsg_copy_hdr(struct io_kiocb *req,
>> if (copy_from_user(iomsg->fast_iov, uiov, sizeof(*uiov)))
>> return -EFAULT;
>> sr->len = iomsg->fast_iov[0].iov_len;
>> - iomsg->iov = NULL;
>> + iomsg->free_iov = NULL;
>> } else {
>> + iomsg->free_iov = iomsg->fast_iov;
>
> The same here...
>
>> ret = __import_iovec(READ, uiov, iov_len, UIO_FASTIOV,
>> - &iomsg->iov, &iomsg->msg.msg_iter,
>> + &iomsg->free_iov, &iomsg->msg.msg_iter,
>> false);
>> if (ret > 0)
>> ret = 0;
>> @@ -4746,10 +4746,11 @@ static int __io_compat_recvmsg_copy_hdr(struct io_kiocb *req,
>> if (clen < 0)
>> return -EINVAL;
>> sr->len = clen;
>> - iomsg->iov = NULL;
>> + iomsg->free_iov = NULL;
>> } else {
>> + iomsg->free_iov = iomsg->fast_iov;
>
> And here...
>
>> ret = __import_iovec(READ, (struct iovec __user *)uiov, len,
>> - UIO_FASTIOV, &iomsg->iov,
>> + UIO_FASTIOV, &iomsg->free_iov,
>> &iomsg->msg.msg_iter, true);
>> if (ret < 0)
>> return ret;
>
>> @@ -4872,8 +4867,8 @@ static int io_recvmsg(struct io_kiocb *req, bool force_nonblock,
>>
>> if (req->flags & REQ_F_BUFFER_SELECTED)
>> cflags = io_put_recv_kbuf(req);
>> - if (kmsg->iov != kmsg->fast_iov)
>> - kfree(kmsg->iov);
>> + if (kmsg->free_iov)
>> + kfree(kmsg->free_iov);
>
> kfree() handles NULL, or is this a hot path and we want to avoid a function call?
Yes, the hot path here is not having iov allocated, and Jens told before
that he had observed overhead for a similar place in io_[read,write].
--
Pavel Begunkov
