Re: [PATCH 5/7] mm/mm_init.c: Extend init unavailable range doc info

From: Mike Rapoport <rppt@kernel.org>
To: Serge Semin <fancer.lancer@gmail.com>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
	Andrew Morton <akpm@linux-foundation.org>,
	Matthew Wilcox <willy@infradead.org>,
	Alexey Malahov <Alexey.Malahov@baikalelectronics.ru>,
	Arnd Bergmann <arnd@arndb.de>,
	Aleksandar Rikalo <aleksandar.rikalo@syrmia.com>,
	Aleksandar Rikalo <arikalo@gmail.com>,
	Dragan Mladjenovic <dragan.mladjenovic@syrmia.com>,
	Chao-ying Fu <cfu@wavecomp.com>,
	Jiaxun Yang <jiaxun.yang@flygoat.com>,
	Yinglu Yang <yangyinglu@loongson.cn>,
	Tiezhu Yang <yangtiezhu@loongson.cn>,
	Marc Zyngier <maz@kernel.org>,
	linux-mips@vger.kernel.org, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 5/7] mm/mm_init.c: Extend init unavailable range doc info
Date: Thu, 23 Nov 2023 12:18:54 +0200	[thread overview]
Message-ID: <20231123101854.GF636165@kernel.org> (raw)
In-Reply-To: <20231122182419.30633-6-fancer.lancer@gmail.com>

Hi Serge,

On Wed, Nov 22, 2023 at 09:24:03PM +0300, Serge Semin wrote:
> Besides of the already described reasons the pages backended memory holes
> might be persistent due to having memory mapped IO spaces behind those
> ranges in the framework of flatmem kernel config. Add such note to the
> init_unavailable_range() method kdoc in order to point out to one more
> reason of having the function executed for such regions.
> 
> Signed-off-by: Serge Semin <fancer.lancer@gmail.com>
> 
> ---
> 
> Please let me know if the IO-space pages must be initialized somehow
> differently rather relying on free_area_init() executing the
> init_unavailable_range() method.

Maybe I'm missing something, but why do you need struct pages in the
IO space?

> ---
>  mm/mm_init.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/mm/mm_init.c b/mm/mm_init.c
> index 077bfe393b5e..3fa33e2d32ba 100644
> --- a/mm/mm_init.c
> +++ b/mm/mm_init.c
> @@ -796,6 +796,7 @@ overlap_memmap_init(unsigned long zone, unsigned long *pfn)
>   * - physical memory bank size is not necessarily the exact multiple of the
>   *   arbitrary section size
>   * - early reserved memory may not be listed in memblock.memory
> + * - memory mapped IO space
>   * - memory layouts defined with memmap= kernel parameter may not align
>   *   nicely with memmap sections
>   *
> -- 
> 2.42.1
> 

-- 
Sincerely yours,
Mike.