On 05/02/2021 09:58, 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.
> I think that should at least get a comment to make this clear and
> maybe a temporary variable like this:
>
> tmp_iov = iomsg->fast_iov;
> __import_iovec(..., &tmp_iov, ...);
> iomsg->free_iov = tmp_iov;
I'd rather disagree. It's a well known (ish) API, and I deliberately
placed such assignments right before import_iovec/etc.
We have been using the same pattern has been used for reads/writes and
io_import_iovec() for ages, but seems it haven't got its attention.
>
>>>> @@ -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].
>
> Ok, a comment would also help here...
>
> metze
>
>
--
Pavel Begunkov
