linux-kernel - Re: [RFC PATCH v3 06/12] memory-provider: dmabuf devmem memory provider

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Message-ID: <583db67b-96c6-4e17-bea0-b5a14799db4a@kernel.org>
Date:   Mon, 6 Nov 2023 16:49:20 -0700
From:   David Ahern <dsahern@...nel.org>
To:     Mina Almasry <almasrymina@...gle.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-kselftest@...r.kernel.org, linux-media@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linaro-mm-sig@...ts.linaro.org
Cc:     "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        Arnd Bergmann <arnd@...db.de>,
        Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        Shuah Khan <shuah@...nel.org>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Christian König <christian.koenig@....com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Jeroen de Borst <jeroendb@...gle.com>,
        Praveen Kaligineedi <pkaligineedi@...gle.com>,
        Willem de Bruijn <willemb@...gle.com>,
        Kaiyuan Zhang <kaiyuanz@...gle.com>
Subject: Re: [RFC PATCH v3 06/12] memory-provider: dmabuf devmem memory
 provider

On 11/5/23 7:44 PM, Mina Almasry wrote:
> diff --git a/include/net/page_pool/helpers.h b/include/net/page_pool/helpers.h
> index 78cbb040af94..b93243c2a640 100644
> --- a/include/net/page_pool/helpers.h
> +++ b/include/net/page_pool/helpers.h
> @@ -111,6 +112,45 @@ page_pool_iov_binding(const struct page_pool_iov *ppiov)
>  	return page_pool_iov_owner(ppiov)->binding;
>  }
>  
> +static inline int page_pool_iov_refcount(const struct page_pool_iov *ppiov)
> +{
> +	return refcount_read(&ppiov->refcount);
> +}
> +
> +static inline void page_pool_iov_get_many(struct page_pool_iov *ppiov,
> +					  unsigned int count)
> +{
> +	refcount_add(count, &ppiov->refcount);
> +}
> +
> +void __page_pool_iov_free(struct page_pool_iov *ppiov);
> +
> +static inline void page_pool_iov_put_many(struct page_pool_iov *ppiov,
> +					  unsigned int count)
> +{
> +	if (!refcount_sub_and_test(count, &ppiov->refcount))
> +		return;
> +
> +	__page_pool_iov_free(ppiov);
> +}
> +
> +/* page pool mm helpers */
> +
> +static inline bool page_is_page_pool_iov(const struct page *page)
> +{
> +	return (unsigned long)page & PP_DEVMEM;

This is another one where the code can be more generic to not force a
lot changes later.  e.g., PP_CUSTOM or PP_NO_PAGE. Then io_uring use
case with host memory can leverage the iov pool in a similar manner.

That does mean skb->devmem needs to be a flag on the page pool and not
just assume iov == device memory.