linux-kernel - Re: [PATCH net-next v4 1/5] page_pool: frag API support for 32-bit arch with 64-bit DMA

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Date:   Tue, 13 Jun 2023 20:55:18 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Yunsheng Lin <linyunsheng@...wei.com>
Cc:     Alexander Lobakin <aleksander.lobakin@...el.com>,
        <davem@...emloft.net>, <pabeni@...hat.com>,
        <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        Lorenzo Bianconi <lorenzo@...nel.org>,
        Alexander Duyck <alexander.duyck@...il.com>,
        Saeed Mahameed <saeedm@...dia.com>,
        Leon Romanovsky <leon@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        <linux-rdma@...r.kernel.org>
Subject: Re: [PATCH net-next v4 1/5] page_pool: frag API support for 32-bit
 arch with 64-bit DMA

On Wed, 14 Jun 2023 11:36:28 +0800 Yunsheng Lin wrote:
> > As Jakub previously mentioned, this involves including dma-mapping.h,
> > which is relatively heavy, to each source file which includes skbuff.h,
> > i.e. almost the whole kernel :D  
> 
> I am not sure I understand the part about 'includes skbuff.h' yet, it seems
> 'skbuff.h' does not have anything related to this patch?

$ git grep net/page_pool.h -- include/linux/skbuff.h
include/linux/skbuff.h:#include <net/page_pool.h>

> > I addressed this in my series, which I hope will land soon after yours
> > (sending new revision in 24-48 hours), so you can leave it as it is. Or
> > otherwise you can pick my solution (or come up with your own :D).  
> 
> Do you mean by removing "#include <linux/dma-direction.h>" as dma-mapping.h
> has included dma-direction.h?
> But I am not sure if there is any hard rule about not explicitly including
> a .h which is implicitly included. What if the dma-mapping.h is changed to not
> include dma-direction.h anymore?
> 
> Anyway, it seems it is unlikely to not include dma-direction.h in dma-mapping.h,
> Will remove the "#include <linux/dma-direction.h>" if there is another version
> needed for this patchset:)

The point is that we don't want commonly included headers to pull
in huge dependencies. Please run the preprocessor on
linux/dma-direction.h, you'll see how enormous it is.