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From: Mina Almasry <almasrymina@google.com>
Date: Sat, 16 Dec 2023 14:06:37 -0800
Message-ID: <CAHS8izOLBtjHOqbTS_PiTNe+rTE=jboDWDM9zS108B57vVNcwA@mail.gmail.com>
Subject: Re: [RFC PATCH net-next v1 4/4] net: page_pool: use netmem_t instead
 of struct page in API
To: Shakeel Butt <shakeelb@google.com>
Cc: Jakub Kicinski <kuba@kernel.org>, Yunsheng Lin <linyunsheng@huawei.com>, 
	linux-kernel@vger.kernel.org, netdev@vger.kernel.org, bpf@vger.kernel.org, 
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On Sat, Dec 16, 2023 at 11:47=E2=80=AFAM Shakeel Butt <shakeelb@google.com>=
 wrote:
>
> On Fri, Dec 15, 2023 at 7:01=E2=80=AFPM Jakub Kicinski <kuba@kernel.org> =
wrote:
> >
> > On Fri, 15 Dec 2023 02:11:14 +0000 Shakeel Butt wrote:
> > > > From my POV it has to be the first one. We want to abstract the mem=
ory
> > > > type from the drivers as much as possible, not introduce N new memo=
ry
> > > > types and ask the driver to implement new code for each of them
> > > > separately.
> > >
> > > Agree with Mina's point. Let's aim to decouple memory types from
> > > drivers.
> >
> > What does "decouple" mean? Drivers should never convert netmem
> > to pages. Either a path in the driver can deal with netmem,
> > i.e. never touch the payload, or it needs pages.
>

I'm guessing the paths in the driver that need pages will have to be
disabled for non-paged netmem, which is fine.

One example that I ran into with GVE is that it calls page_address()
to copy small packets instead of adding them as a frag. I can add a
netmem_address() that returns page_address() for pages, and NULL for
non-pages (never passing non-pages to mm code). The driver can detect
that the netmem has no address, and disable the optimization for
non-paged netmem.

> "Decouple" might not be the right word. What I wanted to say was to
> avoid too much specialization such that we have to have a new API for
> every new fancy thing.
>
> >
> > Perhaps we should aim to not export netmem_to_page(),
> > prevent modules from accessing it directly.
>
> +1.

This is an aggressive approach and I like it. I'll try to make it work
(should be fine).


--
Thanks,
Mina