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

From: Matteo Croce <mcroce@linux.microsoft.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: netdev@vger.kernel.org, linux-mm@kvack.org,
	Ayush Sawal <ayush.sawal@chelsio.com>,
	Vinay Kumar Yadav <vinay.yadav@chelsio.com>,
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	Jakub Kicinski <kuba@kernel.org>,
	Thomas Petazzoni <thomas.petazzoni@bootlin.com>,
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	Russell King <linux@armlinux.org.uk>,
	Mirko Lindner <mlindner@marvell.com>,
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	Tariq Toukan <tariqt@nvidia.com>,
	Jesper Dangaard Brouer <hawk@kernel.org>,
	Ilias Apalodimas <ilias.apalodimas@linaro.org>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
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	Boris Pismenny <borisp@nvidia.com>, Arnd Bergmann <arnd@arndb.de>,
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	Guillaume Nault <gnault@redhat.com>,
	linux-kernel@vger.kernel.org, linux-rdma@vger.kernel.org,
	bpf@vger.kernel.org, Eric Dumazet <edumazet@google.com>,
	David Ahern <dsahern@gmail.com>,
	Lorenzo Bianconi <lorenzo@kernel.org>,
	Saeed Mahameed <saeedm@nvidia.com>, Andrew Lunn <andrew@lunn.ch>,
	Paolo Abeni <pabeni@redhat.com>,
	Sven Auhagen <sven.auhagen@voleatech.de>
Subject: Re: [PATCH net-next v7 1/5] mm: add a signature in struct page
Date: Mon, 7 Jun 2021 15:58:23 +0200	[thread overview]
Message-ID: <CAFnufp1fF5NtM_NzhVG6MmRwkvDot+usPdAOhHdfQUVCHhV75w@mail.gmail.com> (raw)
In-Reply-To: <YL4kpntfzMBXGSfV@casper.infradead.org>

On Mon, Jun 7, 2021 at 3:53 PM Matthew Wilcox <willy@infradead.org> wrote:
>
> On Sun, Jun 06, 2021 at 03:50:54AM +0200, Matteo Croce wrote:
> > And change all the *_pfmemalloc functions to use page->lru.next like this?
> >
> > @@ -1668,10 +1668,12 @@ struct address_space *page_mapping(struct page *page);
> > static inline bool page_is_pfmemalloc(const struct page *page)
> > {
> >        /*
> > -        * Page index cannot be this large so this must be
> > -        * a pfmemalloc page.
> > +        * This is not a tail page; compound_head of a head page is unused
> > +        * at return from the page allocator, and will be overwritten
> > +        * by callers who do not care whether the page came from the
> > +        * reserves.
> >         */
>
> The comment doesn't make a lot of sense if we're switching to use
> lru.next.  How about:
>
>         /*
>          * lru.next has bit 1 set if the page is allocated from the
>          * pfmemalloc reserves.  Callers may simply overwrite it if
>          * they do not need to preserve that information.
>          */

Sounds good!

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