netdev - Re: [PATCH net-next v7 1/5] mm: add a signature in struct page

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Message-ID: <YLp6D7mEh85vL+pY@casper.infradead.org>
Date:   Fri, 4 Jun 2021 20:07:59 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Matteo Croce <mcroce@...ux.microsoft.com>
Cc:     netdev@...r.kernel.org, linux-mm@...ck.org,
        Ayush Sawal <ayush.sawal@...lsio.com>,
        Vinay Kumar Yadav <vinay.yadav@...lsio.com>,
        Rohit Maheshwari <rohitm@...lsio.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Marcin Wojtas <mw@...ihalf.com>,
        Russell King <linux@...linux.org.uk>,
        Mirko Lindner <mlindner@...vell.com>,
        Stephen Hemminger <stephen@...workplumber.org>,
        Tariq Toukan <tariqt@...dia.com>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
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        Sven Auhagen <sven.auhagen@...eatech.de>
Subject: Re: [PATCH net-next v7 1/5] mm: add a signature in struct page

On Fri, Jun 04, 2021 at 08:33:45PM +0200, Matteo Croce wrote:
> @@ -130,7 +137,10 @@ struct page {
>  			};
>  		};
>  		struct {	/* Tail pages of compound page */
> -			unsigned long compound_head;	/* Bit zero is set */
> +			/* Bit zero is set
> +			 * Bit one if pfmemalloc page
> +			 */
> +			unsigned long compound_head;

I would drop this hunk.  Bit 1 is not used for this purpose in tail
pages; it's used for that purpose in head and base pages.

I suppose we could do something like ...

 static inline void set_page_pfmemalloc(struct page *page)
 {
-	page->index = -1UL;
+	page->lru.next = (void *)2;
 }

if it's causing confusion.