Re: [PATCH 3/5] tcp, flow: Replace per-connection in_epoll flag with epollfd in flow_common

[Stefano Brivio <sbrivio@redhat.com>]

On Tue, 7 Oct 2025 17:07:37 +1100
David Gibson <david@gibson.dropbear.id.au> wrote:

> On Fri, Oct 03, 2025 at 05:27:15PM +0200, Laurent Vivier wrote:
> > The in_epoll boolean flag in tcp_tap_conn and tcp_splice_conn only tracked
> > whether a connection was registered with epoll, not which epoll instance.
> > This limited flexibility for future multi-epoll support.
> > 
> > Replace the boolean with an epollfd field in flow_common that serves dual
> > purpose: zero indicates not registered (replacing in_epoll=false), non-zero  
> 
> Don't use 0, since that's a valid fd.
> 
> > stores the actual epoll fd (replacing in_epoll=true).  
> 
> I am a bit nervous about adding 31-bits to every flow, since I think
> we're fairly close to a cacheline threshold.

I mentioned to Laurent in our weekly call on Monday the same concern
and that I would look into it (first step, I would say, actually check
with pahole?) and, if it's an issue, into possible tricks to avoid
making the struct too big. I still plan to do this.

-- 
Stefano