netdev - Re: [RFC, PATCH] net: page_pool: Don't use page->private to store dma_addr

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Message-ID: <20190207213400.GA21860@bombadil.infradead.org>
Date:   Thu, 7 Feb 2019 13:34:00 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     David Miller <davem@...emloft.net>
Cc:     ilias.apalodimas@...aro.org, brouer@...hat.com,
        tariqt@...lanox.com, toke@...hat.com, netdev@...r.kernel.org,
        mgorman@...hsingularity.net, linux-mm@...ck.org
Subject: Re: [RFC, PATCH] net: page_pool: Don't use page->private to store
 dma_addr_t

On Thu, Feb 07, 2019 at 01:25:19PM -0800, David Miller wrote:
> From: Ilias Apalodimas <ilias.apalodimas@...aro.org>
> Date: Thu, 7 Feb 2019 17:20:34 +0200
> 
> > Well updating struct page is the final goal, hence the comment. I am mostly
> > looking for opinions here since we are trying to store dma addresses which are
> > irrelevant to pages. Having dma_addr_t definitions in mm-related headers is a
> > bit controversial isn't it ? If we can add that, then yes the code would look
> > better
> 
> I fundamentally disagree.
> 
> One of the core operations performed on a page is mapping it so that a device
> and use it.
> 
> Why have ancillary data structure support for this all over the place, rather
> than in the common spot which is the page.
> 
> A page really is not just a 'mm' structure, it is a system structure.

+1

The fundamental point of computing is to do I/O.