Re: [PATCH RFC 0/6] copy aside frags with destructors (was [PATCH 7/9] net: add skb_orphan_frags to copy aside frags with destructors)

On Tue, May 08, 2012 at 11:54:11AM +0100, Ian Campbell wrote:

On Tue, 2012-05-08 at 10:41 +0100, Michael S. Tsirkin wrote:

quoted

On Mon, May 07, 2012 at 04:53:46PM +0300, Michael S. Tsirkin wrote:

quoted

quoted

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But I fear we're about to toss Ian into yet another rabbit hole. :-)

Let's try to converge on something quickly as I think integration of
his work has been delayed enough as-is.

...

quoted

Here's a first stub at a fix. Basically to be able to modify frags on
the fly we must make sure the skb isn't cloned, so the moment someone
clones the skb we need to trigger the frag copy logic.  And this is
exactly what happens with SKBTX_DEV_ZEROCOPY so it seems to make sense
to reuse that logic.

The below patchset replaces patch 7
([PATCH 7/9] net: add skb_orphan_frags to copy aside frags with destructors)
in Ian's patchset and needs to be applied there.


Compiled only but I'd like to hear what people think all the same
because it does add a couple of branches on fast path.  On the other
hand this makes it generic so the same logic will be reusable for packet
sockets (which IIRC are currently buggy in the same way as sunrpc) and
for adding zero copy support to tun.

Please comment,
Thanks!

Ian, just to stress, need your ack that this does what you wanted.

Sure, yesterday was a public holiday and today looks likely to be crazy
busy. I'll try and have a look later in the week.

Ian.

In case you or anyone else has cycles to test this, here's the
updated tree, net-next based - so far I verified that it builds and boots
and regular networking works, but didn't test nfs yet.

git://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost.git refs/heads/zerocopy