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

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Date:   Mon, 11 Feb 2019 04:12:08 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     Tariq Toukan <tariqt@...lanox.com>
Cc:     Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        David Miller <davem@...emloft.net>,
        "brouer@...hat.com" <brouer@...hat.com>,
        "toke@...hat.com" <toke@...hat.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "mgorman@...hsingularity.net" <mgorman@...hsingularity.net>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [RFC, PATCH] net: page_pool: Don't use page->private to store
 dma_addr_t

On Mon, Feb 11, 2019 at 08:53:19AM +0000, Tariq Toukan wrote:
> It's great to use the struct page to store its dma mapping, but I am 
> worried about extensibility.
> page_pool is evolving, and it would need several more per-page fields. 
> One of them would be pageref_bias, a planned optimization to reduce the 
> number of the costly atomic pageref operations (and replace existing 
> code in several drivers).

There's space for five words (20 or 40 bytes on 32/64 bit).