Subject: Re: [PATCH v2] tcp: splice as many packets as possible at once

From: Willy Tarreau <[email-masked]>
Date: Fri, 6 Feb 2009 12:10:15 +0100

On Fri, Feb 06, 2009 at 10:58:07AM +0000, Jarek Poplawski wrote:
> On Fri, Feb 06, 2009 at 09:28:22PM +1100, Herbert Xu wrote:
> > On Fri, Feb 06, 2009 at 09:51:20AM +0000, Jarek Poplawski wrote:
> > >
> > > OK, but since there is not so much difference, and we need to waste
> > > it in some cases anyway, plus handle it later some special way, I'm
> > > a bit in doubt.
> > 
> > Well the thing is cards that don't support SG on tx probably
> > don't support jumbo frames either.
> 
> ?? I mean this 128 byte chunk would be hard to reuse after copying
> to skb->data, and if reused, we could miss this for some NICs on TX,
> so the whole packed would need a copy.

couldn't we stuff up to 32 128-byte chunks in a page and use a 32-bit
map to indicate which slot is used and which one is free ? This would
just be a matter of calling ffz() to find one spare place in a page.
Also, that bitmap might serve as a refcount, because if it drops to
zero, it means all slots are unused. And -1 means all slots are used.

This would reduce wastage if wee need to allocate 128 bytes often.

Willy