From: Jarek Poplawski

Date: Tue, 3 Feb 2009 09:41:08 +0000
> Yes, this looks reasonable. On the other hand, I think it would be

quoted text
> nice to get some opinions of slab folks (incl. Evgeniy) on the expected

> efficiency of such a solution. (It seems releasing with put_page() will

> always have some cost with delayed reusing and/or waste of space.)

I think we can't avoid using carved up pages for skb->data in the end.

The whole kernel wants to speak in pages and be able to grab and

release them in one way and one way only (get_page() and put_page()).
What do you think is more likely?  Us teaching the whole entire kernel

how to hold onto SKB linear data buffers, or the networking fixing

itself to operate on pages for it's header metadata? :-)
What we'll end up with is likely a hybrid scheme.  High speed devices

will receive into pages.  And also the skb->data area will be page

backed and held using get_page()/put_page() references.
It is not even worth optimizing for skb->data holding the entire

packet, that's not the case that matters.
These skb->data areas will thus be 128 bytes plus the skb_shinfo

structure blob.  They also will be recycled often, rather than held

onto for long periods of time.
In fact we can optimize that even further in many ways, for example by

dropping the skb->data backed memory once the skb is queued to the

socket receive buffer.  That will make skb->data buffer lifetimes

miniscule even under heavy receive load.
In that kind of situation, doing even the most stupidest page slicing

algorithm, similar to what we do now with sk->sk_sndmsg_page, is

more than adequate and things like NTA (purely to solve this problem)

is overengineering.
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