Re: [PATCH v1 03/15] net: generalise net_iov chunk owners

David Wei
2024-10-11T18:44:40Z

On 2024-10-09 09:28, Stanislav Fomichev wrote:
> On 10/08, Pavel Begunkov wrote:
>> On 10/8/24 16:46, Stanislav Fomichev wrote:
>>> On 10/07, David Wei wrote:
>>>> From: Pavel Begunkov <asml.silence@gmail.com>
>>>>
>>>> Currently net_iov stores a pointer to struct dmabuf_genpool_chunk_owner,
>>>> which serves as a useful abstraction to share data and provide a
>>>> context. However, it's too devmem specific, and we want to reuse it for
>>>> other memory providers, and for that we need to decouple net_iov from
>>>> devmem. Make net_iov to point to a new base structure called
>>>> net_iov_area, which dmabuf_genpool_chunk_owner extends.
>>>>
>>>> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
>>>> Signed-off-by: David Wei <dw@davidwei.uk>
>>>> ---
>>>> include/net/netmem.h | 21 ++++++++++++++++++++-
>>>> net/core/devmem.c | 25 +++++++++++++------------
>>>> net/core/devmem.h | 25 +++++++++----------------
>>>> 3 files changed, 42 insertions(+), 29 deletions(-)
>>>>
>>>> diff --git a/include/net/netmem.h b/include/net/netmem.h
>>>> index 8a6e20be4b9d..3795ded30d2c 100644
>>>> --- a/include/net/netmem.h
>>>> +++ b/include/net/netmem.h
>>>> @@ -24,11 +24,20 @@ struct net_iov {
>>>> unsigned long __unused_padding;
>>>> unsigned long pp_magic;
>>>> struct page_pool *pp;
>>>> - struct dmabuf_genpool_chunk_owner *owner;
>>>> + struct net_iov_area *owner;
>>>
>>> Any reason not to use dmabuf_genpool_chunk_owner as is (or rename it
>>> to net_iov_area to generalize) with the fields that you don't need
>>> set to 0/NULL? container_of makes everything harder to follow :-(
>>
>> It can be that, but then io_uring would have a (null) pointer to
>> struct net_devmem_dmabuf_binding it knows nothing about and other
>> fields devmem might add in the future. Also, it reduces the
>> temptation for the common code to make assumptions about the origin
>> of the area / pp memory provider. IOW, I think it's cleaner
>> when separated like in this patch.
>
> Ack, let's see whether other people find any issues with this approach.
> For me, it makes the devmem parts harder to read, so my preference
> is on dropping this patch and keeping owner=null on your side.

I don't mind at this point which approach to take right now. I would
prefer keeping dmabuf_genpool_chunk_owner today even if it results in a
nullptr in io_uring's case. Once there are more memory providers in the
future, I think it'll be clearer what sort of abstraction we might need
here.