Re: [PATCH net-next 2/7] rds: hold a sock ref from rds_message to the rds_sock

On Sun, Jan 28, 2018 at 5:18 PM, Sowmini Varadhan
[off-list ref] wrote:

On (01/28/18 14:51), Willem de Bruijn wrote:

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On (01/25/18 15:44), Willem de Bruijn wrote:

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You may alos be able to do the same as tcp zerocopy and
hold an sk reference on the notification skb.

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I don't quite follow. Every notification skb is created when pages refcount
is increased. It persists until at least rds_rm_zerocopy_callback, after data
skb has been freed and pages refcount has been decreased.

In this callback, skb is consumed if another skb is already queued on
the error queue, otherwise it is queued itself. It needs to hold a sock ref
until it can be queued.

maybe I did not follow the original suggestion- were you
suggesting that I hold a pointer to the sk from e.g., the skb->cb
itself?

Yes, I mean associating the notification skb that is eventually
queued onto the error queue with the socket. For tcp zerocopy,
this happens implicitly in sock_omalloc.

I dont know that it would make things simpler,
whereas having the pointer and refcount in the rds_message itself,
and track this independantly of whether/not zcopy was used, seems
like a more consistent dsta-structure model, so I'd like to leave
this as is.

Sounds good. You know the rds internals a lot better than I do,
so are the better judge on whether to choose that or sock_omalloc.