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

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Message-ID: <20190207150745.GW21860@bombadil.infradead.org>
Date:   Thu, 7 Feb 2019 07:07:45 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     Ilias Apalodimas <ilias.apalodimas@...aro.org>
Cc:     brouer@...hat.com, tariqt@...lanox.com, toke@...hat.com,
        davem@...emloft.net, 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 04:36:36PM +0200, Ilias Apalodimas wrote:
> +/* Until we can update struct-page, have a shadow struct-page, that
> + * include our use-case
> + * Used to store retrieve dma addresses from network drivers.
> + * Never access this directly, use helper functions provided
> + * page_pool_get_dma_addr()
> + */

Huh?  Why not simply:

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 2c471a2c43fa..2495a93ad90c 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -28,6 +28,10 @@ struct address_space;
 struct mem_cgroup;
 struct hmm;
 
+struct page_pool {
+       dma_addr_t dma_addr;
+};
+
 /*
  * Each physical page in the system has a struct page associated with
  * it to keep track of whatever it is we are using the page for at the
@@ -77,6 +81,7 @@ struct page {
         * avoid collision and false-positive PageTail().
         */
        union {
+               struct page_pool pool;
                struct {        /* Page cache and anonymous pages */
                        /**
                         * @lru: Pageout list, eg. active_list protected by