From: Eric Dumazet <edumazet@google.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: Ilias Apalodimas <ilias.apalodimas@linaro.org>,
Matteo Croce <mcroce@linux.microsoft.com>,
Networking <netdev@vger.kernel.org>,
Linux-MM <linux-mm@kvack.org>,
Ayush Sawal <ayush.sawal@chelsio.com>,
Vinay Kumar Yadav <vinay.yadav@chelsio.com>,
Rohit Maheshwari <rohitm@chelsio.com>,
"David S. Miller" <davem@davemloft.net>,
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>,
Stephen Hemminger <stephen@networkplumber.org>,
Tariq Toukan <tariqt@nvidia.com>,
Jesper Dangaard Brouer <hawk@kernel.org>,
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John Fastabend <john.fastabend@gmail.com>,
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Willem de Bruijn <willemb@google.com>,
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Yunsheng Lin <linyunsheng@huawei.com>,
Guillaume Nault <gnault@redhat.com>,
open list <linux-kernel@vger.kernel.org>,
linux-rdma <linux-rdma@vger.kernel.org>,
bpf <bpf@vger.kernel.org>, 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 v4 1/4] mm: add a signature in struct page
Date: Wed, 12 May 2021 18:09:21 +0200 [thread overview]
Message-ID: <CANn89iJ7j4-rm+i58RMcB8Fahe6yEao7jhDUe_M9U6L67nZ1gA@mail.gmail.com> (raw)
In-Reply-To: <YJv65eER2qgaP9Ib@casper.infradead.org>
On Wed, May 12, 2021 at 6:03 PM Matthew Wilcox <willy@infradead.org> wrote:
>
> On Tue, May 11, 2021 at 05:25:36PM +0300, Ilias Apalodimas wrote:
> > Nope not at all, either would work. we'll switch to that
>
> You'll need something like this because of the current use of
> page->index to mean "pfmemalloc".
>
> From ecd6d912056a21bbe55d997c01f96b0b8b9fbc31 Mon Sep 17 00:00:00 2001
> From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
> Date: Fri, 16 Apr 2021 18:12:33 -0400
> Subject: [PATCH] mm: Indicate pfmemalloc pages in compound_head
>
> The net page_pool wants to use a magic value to identify page pool pages.
> The best place to put it is in the first word where it can be clearly a
> non-pointer value. That means shifting dma_addr up to alias with ->index,
> which means we need to find another way to indicate page_is_pfmemalloc().
> Since page_pool doesn't want to set its magic value on pages which are
> pfmemalloc, we can use bit 1 of compound_head to indicate that the page
> came from the memory reserves.
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> ---
> include/linux/mm.h | 12 +++++++-----
> include/linux/mm_types.h | 7 +++----
> 2 files changed, 10 insertions(+), 9 deletions(-)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index bd21864449bf..4f9b2007efad 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1670,10 +1670,12 @@ 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.
> */
> - return page->index == -1UL;
> + return page->compound_head & 2;
> }
>
> /*
> @@ -1682,12 +1684,12 @@ static inline bool page_is_pfmemalloc(const struct page *page)
> */
> static inline void set_page_pfmemalloc(struct page *page)
> {
> - page->index = -1UL;
> + page->compound_head = 2;
> }
>
> static inline void clear_page_pfmemalloc(struct page *page)
> {
> - page->index = 0;
> + page->compound_head = 0;
> }
>
> /*
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index 5aacc1c10a45..1352e278939b 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -96,10 +96,9 @@ struct page {
> unsigned long private;
> };
> struct { /* page_pool used by netstack */
> - /**
> - * @dma_addr: might require a 64-bit value on
> - * 32-bit architectures.
> - */
> + unsigned long pp_magic;
> + struct page_pool *pp;
> + unsigned long _pp_mapping_pad;
> unsigned long dma_addr[2];
> };
> struct { /* slab, slob and slub */
> --
> 2.30.2
>
This would break compound_head() ?
next prev parent reply other threads:[~2021-05-12 18:38 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-11 13:31 [PATCH net-next v4 0/4] page_pool: recycle buffers Matteo Croce
2021-05-11 13:31 ` [PATCH net-next v4 1/4] mm: add a signature in struct page Matteo Croce
2021-05-11 13:45 ` Matthew Wilcox
2021-05-11 14:11 ` Ilias Apalodimas
2021-05-11 14:18 ` Matthew Wilcox
2021-05-11 14:25 ` Ilias Apalodimas
2021-05-12 15:57 ` Matthew Wilcox
2021-05-12 16:09 ` Eric Dumazet [this message]
2021-05-12 16:26 ` Matthew Wilcox
2021-05-12 16:47 ` Ilias Apalodimas
2021-05-13 2:15 ` Yunsheng Lin
2021-05-13 2:35 ` Matthew Wilcox
2021-05-13 3:25 ` Yunsheng Lin
2021-05-11 13:31 ` [PATCH net-next v4 2/4] page_pool: Allow drivers to hint on SKB recycling Matteo Croce
2021-05-11 15:24 ` Eric Dumazet
2021-05-12 9:50 ` Ilias Apalodimas
2021-05-12 14:09 ` Eric Dumazet
2021-05-12 14:39 ` Ilias Apalodimas
2021-05-11 13:31 ` [PATCH net-next v4 3/4] mvpp2: recycle buffers Matteo Croce
2021-05-11 13:31 ` [PATCH net-next v4 4/4] mvneta: " Matteo Croce
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