Received-SPF: pass (google.com: domain of linux-nfs-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
From:   Chuck Lever <chuck.lever@oracle.com>
To:     Tom Talpey <tom@talpey.com>
CC:     Anna Schumaker <anna.schumaker@netapp.com>,
        Linux NFS Mailing List <linux-nfs@vger.kernel.org>,
        "linux-rdma@vger.kernel.org" <linux-rdma@vger.kernel.org>
Subject: Re: [PATCH v1] xprtrdma: Simplify rpcrdma_convert_kvec() and
 frwr_map()
Thread-Topic: [PATCH v1] xprtrdma: Simplify rpcrdma_convert_kvec() and
 frwr_map()
Thread-Index: AQHW+XI3YU9+0Px6s0a/A4oYM4MFE6pFPVyAgAAAmgA=
Date:   Tue, 2 Feb 2021 19:20:13 +0000
Message-ID: <B0EED542-086B-4E76-9348-FAB8EBA612AB@oracle.com>
References: <161227696787.3689758.305854118266206775.stgit@manet.1015granger.net>
 <e53cc3c2-2209-5f35-c487-9e59b9b9e526@talpey.com>
In-Reply-To: <e53cc3c2-2209-5f35-c487-9e59b9b9e526@talpey.com>
Accept-Language: en-US
Content-Language: en-US
Content-Type: text/plain; charset="us-ascii"
Content-ID: <604C6183373499468683E38EA216DF73@namprd10.prod.outlook.com>
Content-Transfer-Encoding: quoted-printable
MIME-Version: 1.0
X-MS-Exchange-CrossTenant-Network-Message-Id: fb3a4bf9-d06b-4470-2d48-08d8c7af9089
X-MS-Exchange-CrossTenant-originalarrivaltime: 02 Feb 2021 19:20:13.0291
 (UTC)
X-MS-Exchange-CrossTenant-fromentityheader: Hosted
X-MS-Exchange-CrossTenant-id: 4e2c6054-71cb-48f1-bd6c-3a9705aca71b
X-MS-Exchange-CrossTenant-mailboxtype: HOSTED
X-MS-Exchange-CrossTenant-userprincipalname: ys79HJ4+7gzMw1DAayug+7tb4t+ZiOtDzzL/RYEWq1cl26V3JU4S5k8iKiFaxUkYgcQZhgdjjqpKTT/60n+KbQ==
X-MS-Exchange-Transport-CrossTenantHeadersStamped: BY5PR10MB3857
X-Proofpoint-Virus-Version: vendor=nai engine=6200 definitions=9883 signatures=668683
X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 malwarescore=0 mlxscore=0
 suspectscore=0 spamscore=0 mlxlogscore=999 phishscore=0 adultscore=0
 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1
 engine=8.12.0-2009150000 definitions=main-2102020123
X-Proofpoint-Virus-Version: vendor=nai engine=6200 definitions=9883 signatures=668683
X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 impostorscore=0 lowpriorityscore=0
 spamscore=0 priorityscore=1501 suspectscore=0 phishscore=0 mlxlogscore=999
 malwarescore=0 clxscore=1011 bulkscore=0 adultscore=0 mlxscore=0
 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000
 definitions=main-2102020122
Precedence: bulk
List-ID: <linux-nfs.vger.kernel.org>
X-Mailing-List: linux-nfs@vger.kernel.org


> On Feb 2, 2021, at 2:18 PM, Tom Talpey <tom@talpey.com> wrote:
>=20
> What's not to like about a log that uses the words "with aplomb"? :)
>=20
> Minor related comment/question below.
>=20
> On 2/2/2021 9:42 AM, Chuck Lever wrote:
>> Clean up.
>> Support for FMR was removed by commit ba69cd122ece ("xprtrdma:
>> Remove support for FMR memory registration") [Dec 2018]. That means
>> the buffer-splitting behavior of rpcrdma_convert_kvec(), added by
>> commit 821c791a0bde ("xprtrdma: Segment head and tail XDR buffers
>> on page boundaries") [Mar 2016], is no longer necessary. FRWR
>> memory registration handles this case with aplomb.
>> A related simplification removes an extra conditional branch from
>> the SGL set-up loop in frwr_map(): Instead of using either
>> sg_set_page() or sg_set_buf(), initialize the mr_page field properly
>> when rpcrdma_convert_kvec() converts the kvec to an SGL entry.
>> frwr_map() can then invoke sg_set_page() unconditionally.
>> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
>> ---
>>  net/sunrpc/xprtrdma/frwr_ops.c  |   10 ++--------
>>  net/sunrpc/xprtrdma/rpc_rdma.c  |   21 +++++----------------
>>  net/sunrpc/xprtrdma/xprt_rdma.h |    2 +-
>>  3 files changed, 8 insertions(+), 25 deletions(-)
>> diff --git a/net/sunrpc/xprtrdma/frwr_ops.c b/net/sunrpc/xprtrdma/frwr_o=
ps.c
>> index baca49fe83af..5eb044a5f0be 100644
>> --- a/net/sunrpc/xprtrdma/frwr_ops.c
>> +++ b/net/sunrpc/xprtrdma/frwr_ops.c
>> @@ -306,14 +306,8 @@ struct rpcrdma_mr_seg *frwr_map(struct rpcrdma_xprt=
 *r_xprt,
>>  	if (nsegs > ep->re_max_fr_depth)
>>  		nsegs =3D ep->re_max_fr_depth;
>>  	for (i =3D 0; i < nsegs;) {
>> -		if (seg->mr_page)
>> -			sg_set_page(&mr->mr_sg[i],
>> -				    seg->mr_page,
>> -				    seg->mr_len,
>> -				    offset_in_page(seg->mr_offset));
>> -		else
>> -			sg_set_buf(&mr->mr_sg[i], seg->mr_offset,
>> -				   seg->mr_len);
>> +		sg_set_page(&mr->mr_sg[i], seg->mr_page,
>> +			    seg->mr_len, offset_in_page(seg->mr_offset));
>>    		++seg;
>>  		++i;
>> diff --git a/net/sunrpc/xprtrdma/rpc_rdma.c b/net/sunrpc/xprtrdma/rpc_rd=
ma.c
>> index 8f5d0cb68360..529adb6ad4db 100644
>> --- a/net/sunrpc/xprtrdma/rpc_rdma.c
>> +++ b/net/sunrpc/xprtrdma/rpc_rdma.c
>> @@ -204,9 +204,7 @@ rpcrdma_alloc_sparse_pages(struct xdr_buf *buf)
>>  	return 0;
>>  }
>>  -/* Split @vec on page boundaries into SGEs. FMR registers pages, not
>> - * a byte range. Other modes coalesce these SGEs into a single MR
>> - * when they can.
>> +/* Convert @vec to a single SGL element.
>>   *
>>   * Returns pointer to next available SGE, and bumps the total number
>>   * of SGEs consumed.
>> @@ -215,21 +213,12 @@ static struct rpcrdma_mr_seg *
>>  rpcrdma_convert_kvec(struct kvec *vec, struct rpcrdma_mr_seg *seg,
>>  		     unsigned int *n)
>>  {
>> -	u32 remaining, page_offset;
>> -	char *base;
>> -
>> -	base =3D vec->iov_base;
>> -	page_offset =3D offset_in_page(base);
>> -	remaining =3D vec->iov_len;
>> -	while (remaining) {
>> -		seg->mr_page =3D NULL;
>> -		seg->mr_offset =3D base;
>> -		seg->mr_len =3D min_t(u32, PAGE_SIZE - page_offset, remaining);
>> -		remaining -=3D seg->mr_len;
>> -		base +=3D seg->mr_len;
>> +	if (vec->iov_len) {
>> +		seg->mr_page =3D virt_to_page(vec->iov_base);
>> +		seg->mr_offset =3D vec->iov_base;
>> +		seg->mr_len =3D vec->iov_len;
>>  		++seg;
>>  		++(*n);
>> -		page_offset =3D 0;
>>  	}
>>  	return seg;
>>  }
>> diff --git a/net/sunrpc/xprtrdma/xprt_rdma.h b/net/sunrpc/xprtrdma/xprt_=
rdma.h
>> index 94b28657aeeb..4a9fe6592795 100644
>> --- a/net/sunrpc/xprtrdma/xprt_rdma.h
>> +++ b/net/sunrpc/xprtrdma/xprt_rdma.h
>> @@ -285,7 +285,7 @@ enum {
>>    struct rpcrdma_mr_seg {		/* chunk descriptors */
>>  	u32		mr_len;		/* length of chunk or segment */
>> -	struct page	*mr_page;	/* owning page, if any */
>> +	struct page	*mr_page;	/* underlying struct page */
>>  	char		*mr_offset;	/* kva if no page, else offset */
>=20
> Is this comment ("kva if no page") actually correct? The hunk just
> above is an example of a case where mr_page is set, yet mr_offset
> is an iov_base. Is iov_base not a kva?

Ah, well the "if no page" part is now obsolete.

I suppose it should be set to "offset_in_page(vec->iov_base)" ?


--
Chuck Lever