linux-kernel - Re: [PATCH RFC 3/8] memory-provider: dmabuf devmem memory provider

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Date:   Wed, 15 Nov 2023 09:38:27 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Yunsheng Lin <linyunsheng@...wei.com>
Cc:     Mina Almasry <almasrymina@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>, davem@...emloft.net,
        pabeni@...hat.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Willem de Bruijn <willemb@...gle.com>,
        Kaiyuan Zhang <kaiyuanz@...gle.com>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Christian König <christian.koenig@....com>,
        Matthew Wilcox <willy@...radead.org>,
        Linux-MM <linux-mm@...ck.org>
Subject: Re: [PATCH RFC 3/8] memory-provider: dmabuf devmem memory provider

On Wed, Nov 15, 2023 at 05:21:02PM +0800, Yunsheng Lin wrote:

> >>> I would expect net stack, page pool, driver still see the 'struct page',
> >>> only memory provider see the specific struct for itself, for the above,
> >>> devmem memory provider sees the 'struct page_pool_iov'.
> >>>
> >>> The reason I still expect driver to see the 'struct page' is that driver
> >>> will still need to support normal memory besides devmem.
> > 
> > I wouldn't say this approach is unreasonable, but it does have to be
> > done carefully to isolate the mm. Keeping the struct page in the API
> > is going to make this very hard.
> 
> I would expect that most of the isolation is done in page pool, as far as
> I can see:

It is the sort of thing that is important enough it should have
compiler help via types to prove that it is being done
properly. Otherwise it will be full of mistakes over time.

Jason