RE: PATCH zero-copy send completion callback

["Eric Barton" <eeb@bartonsoftware.com>]

Evgeniy,

> You can use existing skb destructor and appropriate reference
> counter is already there. In your own destructor you need to
> call old one of course, and it's type can be determined from
> the analysis of the headers and skb itself (there are not so
> much destructor's types actually).  If that level of
> abstraction is not enough, it is possible to change
> skb_release_data()/__kfree_skb() so that it would be possible
> in skb->destructor() to determine if attached pages will be
> freed or not.

Yes absolutely.  My first thought was to use the skbuf destructor
but I was paranoid I might screw up the destructor stacking.
Maybe I should have been braver?

Since the callback descriptor needs to track the pages in
skb_shinfo() rather than the skbuf itself, it seemed "natural"
to make skb_release_data() the trigger.

> Existing sendfile() implementation is synchronous, it does not
> require async callback. 

Is it not true that you cannot know when it is safe to overwrite
pages sent in this way?

> skbs are allocated from own cache, and the smaller it is, the better.

As I mentioned in another reply, skbs are indeed allocated from
their own cache, but skb_shinfo() is allocated contiguously with
the packet header using kmalloc.

-- 

                Cheers,
                        Eric