Re: [PATCH net-next] net: ena: reuse the whole RX page on 64kB page kernels

[Jakub Kicinski <kuba@kernel.org>]

On Fri, 13 Nov 2026 21:35:17 +0000 Arthur Kiyanovski wrote:
> On 2026-11-11 16:47:51-08:00, Jakub Kicinski wrote:
> > On Fri, 06 Nov 2026 03:17:11 +0000 Harry Yoo (Meta) wrote:
> >   
> > > This shows up when RX data stays in socket receive queues, as each
> > > queued skb keeps the whole 64kB page alive while at most 16kB of it
> > > holds data. On an EC2 t4g.large instance (64kB pages, 8GB memory) with
> > > 519MB left unread across 64 TCP sockets, RX pages pinned 2869MB of
> > > memory while the socket layer accounted only 687MB.  
> > 
> > I'm not sure you're actually fixing the problem you're describing?
> > You optimize the memory use but the (unused) tail of the buffer is
> > still not charged to any skb, is it? Or does it now fit perfectly?
> > 
> > Normally when the page can no longer be chunked up we should charge
> > the tail to whoever happened to use it last (see the page pool code
> > which does that).
> > 
> > Either way, you have to respin this on top of Breno's fix which
> > was applied earlier today.  
> 
> 
> Jakub,
> 
> If I understand correctly what you are saying, you are correct.
> skb->truesize is still not reported correctly.
> 
> The focus in this patch is different. It is about using the whole
> 64KB page instead of only the first 16KB.
> 
> Harry's own figures show most of it is recovered — 497MB pinned for
> 519MB unread, against 2869MB before — so the remaining gap is the
> final tail of each page, not the 48kB.
> 
> So I agree the commit message needs to be more precise.
> 
> The skb->truesize fix can come as a separate fix after this one.

You sent it twice? Some LLM automation gone wrong judging by the
m-dashes in your reply? :/

Making more efficient use of allocated pages is not a fix, and
will not be accepted to net or stable. Not accounting truesize 
correctly can be considered a fix. IOW the truesize accounting 
change has to come _first_. Then we can optimize the memory use 
w/ 64kB pages. They can both go to net-next, but the cannot both
go to net.

Hope spelling out practical implications of what I said earlier
makes it clear to everyone..