> On Feb 3, 2021, at 1:06 PM, Tom Talpey <tom@xxxxxxxxxx> wrote:
>
> On 2/3/2021 11:23 AM, Chuck Lever wrote:
>> 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.
>> Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
>> ---
>> net/sunrpc/xprtrdma/rpc_rdma.c | 19 ++++---------------
>> 1 file changed, 4 insertions(+), 15 deletions(-)
>> diff --git a/net/sunrpc/xprtrdma/rpc_rdma.c b/net/sunrpc/xprtrdma/rpc_rdma.c
>> index 8f5d0cb68360..832765f3ebba 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 = vec->iov_base;
>> - page_offset = offset_in_page(base);
>> - remaining = vec->iov_len;
>> - while (remaining) {
>> + if (vec->iov_len) {
>
> This is weird. Is it ever possible for a zero-length segment to be
> passed? If so, it's obviously wrong to return an uninitialized "seg"
> to the caller. I'd suggest simply asserting that iov_len is != 0.
>
> I guess this was an issue in the existing code, but there, it would
> only trigger if *all* the segs were zero.
It would be a bug if head.iov_len was zero.
tail.iov_len is checked before the call. I think that means this
check is superfluous and can be removed.
>
>> seg->mr_page = NULL;
>> - seg->mr_offset = base;
>> - seg->mr_len = min_t(u32, PAGE_SIZE - page_offset, remaining);
>> - remaining -= seg->mr_len;
>> - base += seg->mr_len;
>> + seg->mr_offset = vec->iov_base;
>
> I thought the previous discussion was that this should be offset_in_page
> not the (virtual) iov_base.
Addressed in 3/6?
>
> Tom.
>
>> + seg->mr_len = vec->iov_len;
>> ++seg;
>> ++(*n);
>> - page_offset = 0;
>> }
>> return seg;
>> }
--
Chuck Lever
