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

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Message-Id: <20190207.132519.1698007650891404763.davem@davemloft.net>
Date:   Thu, 07 Feb 2019 13:25:19 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     ilias.apalodimas@...aro.org
Cc:     willy@...radead.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

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.