linux-kernel - Re: [Patch v2 09/15] CIFS: SMBD: Support page offset in RDMA recv

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Date:   Sat, 23 Jun 2018 22:16:15 -0400
From:   Tom Talpey <tom@...pey.com>
To:     longli@...rosoft.com, Steve French <sfrench@...ba.org>,
        linux-cifs@...r.kernel.org, samba-technical@...ts.samba.org,
        linux-kernel@...r.kernel.org, linux-rdma@...r.kernel.org
Subject: Re: [Patch v2 09/15] CIFS: SMBD: Support page offset in RDMA recv

On 5/30/2018 3:48 PM, Long Li wrote:
> From: Long Li <longli@...rosoft.com>
> 
> RDMA recv function needs to place data to the correct place starting at
> page offset.
> 
> Signed-off-by: Long Li <longli@...rosoft.com>
> ---
>   fs/cifs/smbdirect.c | 18 +++++++++++-------
>   1 file changed, 11 insertions(+), 7 deletions(-)
> 
> diff --git a/fs/cifs/smbdirect.c b/fs/cifs/smbdirect.c
> index 6141e3c..ba53c52 100644
> --- a/fs/cifs/smbdirect.c
> +++ b/fs/cifs/smbdirect.c
> @@ -2004,10 +2004,12 @@ static int smbd_recv_buf(struct smbd_connection *info, char *buf,
>    * return value: actual data read
>    */
>   static int smbd_recv_page(struct smbd_connection *info,
> -		struct page *page, unsigned int to_read)
> +		struct page *page, unsigned int page_offset,
> +		unsigned int to_read)
>   {
>   	int ret;
>   	char *to_address;
> +	void *page_address;
>   
>   	/* make sure we have the page ready for read */
>   	ret = wait_event_interruptible(
> @@ -2015,16 +2017,17 @@ static int smbd_recv_page(struct smbd_connection *info,
>   		info->reassembly_data_length >= to_read ||
>   			info->transport_status != SMBD_CONNECTED);
>   	if (ret)
> -		return 0;
> +		return ret;
>   
>   	/* now we can read from reassembly queue and not sleep */
> -	to_address = kmap_atomic(page);
> +	page_address = kmap_atomic(page);
> +	to_address = (char *) page_address + page_offset;
>   
>   	log_read(INFO, "reading from page=%p address=%p to_read=%d\n",
>   		page, to_address, to_read);
>   
>   	ret = smbd_recv_buf(info, to_address, to_read);
> -	kunmap_atomic(to_address);
> +	kunmap_atomic(page_address);

Is "page" truly not mapped? This kmap/kunmap for each received 4KB is
very expensive. Is there not a way to keep a kva for the reassembly
queue segments?

>   
>   	return ret;
>   }
> @@ -2038,7 +2041,7 @@ int smbd_recv(struct smbd_connection *info, struct msghdr *msg)
>   {
>   	char *buf;
>   	struct page *page;
> -	unsigned int to_read;
> +	unsigned int to_read, page_offset;
>   	int rc;
>   
>   	info->smbd_recv_pending++;
> @@ -2052,15 +2055,16 @@ int smbd_recv(struct smbd_connection *info, struct msghdr *msg)
>   
>   	case READ | ITER_BVEC:
>   		page = msg->msg_iter.bvec->bv_page;
> +		page_offset = msg->msg_iter.bvec->bv_offset;
>   		to_read = msg->msg_iter.bvec->bv_len;
> -		rc = smbd_recv_page(info, page, to_read);
> +		rc = smbd_recv_page(info, page, page_offset, to_read);
>   		break;
>   
>   	default:
>   		/* It's a bug in upper layer to get there */
>   		cifs_dbg(VFS, "CIFS: invalid msg type %d\n",
>   			msg->msg_iter.type);
> -		rc = -EIO;
> +		rc = -EINVAL;
>   	}
>   
>   	info->smbd_recv_pending--;
>