linux-kernel - Re: [PATCH net-next v24 08/13] net: add support for skbs with unreadable frags

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Message-ID: <CAHS8izPN8cDVhAzdedr7zb9zmDaiOMqkaDqB07QwVKKEJ62HzQ@mail.gmail.com>
Date: Wed, 4 Sep 2024 08:18:12 -0700
From: Mina Almasry <almasrymina@...gle.com>
To: Jakub Kicinski <kuba@...nel.org>
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Subject: Re: [PATCH net-next v24 08/13] net: add support for skbs with
 unreadable frags

On Tue, Sep 3, 2024 at 2:40 PM Jakub Kicinski <kuba@...nel.org> wrote:
>
> On Sat, 31 Aug 2024 00:43:08 +0000 Mina Almasry wrote:
> >  static inline bool tcp_skb_can_collapse_to(const struct sk_buff *skb)
> >  {
> > -     return likely(!TCP_SKB_CB(skb)->eor);
> > +     return likely(!TCP_SKB_CB(skb)->eor && skb_frags_readable(skb));
>
> Do you remember why this is here?

Yeah, to be honest, when I first implemented some of these checks I
erred on the side of caution, and added checks around anything that
looked concerning, some of these unnecessary checks got removed, but
looks like this one didn't.

> Both for Rx and Tx what should matter
> is whether the "readability" matches, right? We can merge two unreadable
> messages.

Yes, you're right, only 'readability matches' should be the criteria
here. `tcp_skb_can_collapse` already checks readability is matching
correctly, so no issue there. The `tcp_skb_can_collapse_to` check
you're commenting on here looks unnecessary. I will remove it and run
that through some testing.

As an aside, it looks to me like that tcp_skb_can_collapse_to
callsites don't seem to be doing any collapsing. Unless I misread the
code. It looks like tcp_skb_can_collapse_to is used as an eor check. I
can rename the function to tcp_skb_is_eor() or something if that makes
sense (in a separate patch). I think the name of the function confused
me slightly and made me think I need to do a readability check.

--
Thanks,
Mina