netdev - RE: [PATCH 0/6 v2] skb paged fragment destructors

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Date:	Thu, 5 Jan 2012 17:27:31 -0000
From:	"David Laight" <David.Laight@...LAB.COM>
To:	"Ian Campbell" <Ian.Campbell@...rix.com>,
	"David Miller" <davem@...emloft.net>
Cc:	<netdev@...r.kernel.org>, "Eric Dumazet" <eric.dumazet@...il.com>
Subject: RE: [PATCH 0/6 v2] skb paged fragment destructors

 
> The mail at [0] contains some more background and rationale but
> basically the completed series will allow entities which inject pages
> into the networking stack to receive a notification when the stack has
> really finished with those pages (i.e. including retransmissions,
> clones, pull-ups etc) and not just when the original skb is finished
> with, which is beneficial to many subsystems which wish to inject
pages
> into the network stack without giving up full ownership of those
page's
> lifecycle. It implements something broadly along the lines of what was
> described in [1].

If you are doing that, then the network drivers must ensure they
free such skb as soon as the transmit completes - rather than
deferring the 'end of tx' processing until some later time.

Without that the sending code can't reuse the 'page' for another
request - which is one of the things I presume this allows.

(We had issues with this on SVR4 with STREAMS buffers allocated
with esballoc()...)

	David


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