linux-kernel - Re: [PATCH 5.4 1/5] memblock: free_unused_memmap: use pageblock units instead of MAX

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Message-ID: <Ybcg6ZmQCSLbsy17@kernel.org>
Date:   Mon, 13 Dec 2021 12:31:05 +0200
From:   Mike Rapoport <rppt@...nel.org>
To:     Mark-PK Tsai <mark-pk.tsai@...iatek.com>
Cc:     stable@...r.kernel.org, akpm@...ux-foundation.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux@...linux.org.uk, rppt@...ux.ibm.com,
        tony@...mide.com, wangkefeng.wang@...wei.com,
        yj.chiang@...iatek.com
Subject: Re: [PATCH 5.4 1/5] memblock: free_unused_memmap: use pageblock
 units instead of MAX_ORDER

On Mon, Dec 13, 2021 at 04:57:06PM +0800, Mark-PK Tsai wrote:

> Subject: [PATCH 5.4 1/5] memblock: free_unused_memmap: use pageblock units instead of MAX_ORDER

I'd replace memblock: with arm: in the subject. I believe it's clearer this
way.

The same applies for the second patch in the series and for 5.10 posting.

> From: Mike Rapoport <rppt@...ux.ibm.com>
> 
> commit e2a86800d58639b3acde7eaeb9eb393dca066e08 upstream.
> 
> The code that frees unused memory map uses rounds start and end of the
> holes that are freed to MAX_ORDER_NR_PAGES to preserve continuity of the
> memory map for MAX_ORDER regions.
> 
> Lots of core memory management functionality relies on homogeneity of the
> memory map within each pageblock which size may differ from MAX_ORDER in
> certain configurations.
> 
> Although currently, for the architectures that use free_unused_memmap(),
> pageblock_order and MAX_ORDER are equivalent, it is cleaner to have common
> notation thought mm code.
> 
> Replace MAX_ORDER_NR_PAGES with pageblock_nr_pages and update the comments
> to make it more clear why the alignment to pageblock boundaries is
> required.
> 
> Signed-off-by: Mike Rapoport <rppt@...ux.ibm.com>
> Tested-by: Tony Lindgren <tony@...mide.com>
> Link: https://lore.kernel.org/lkml/20210630071211.21011-1-rppt@kernel.org/
> [backport upstream modification in mm/memblock.c to arch/arm/mm/init.c]
> Signed-off-by: Mark-PK Tsai <mark-pk.tsai@...iatek.com>
> ---
>  arch/arm/mm/init.c | 16 ++++++++--------
>  1 file changed, 8 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
> index 7ea4d3b43444..6905dd8bc03f 100644
> --- a/arch/arm/mm/init.c
> +++ b/arch/arm/mm/init.c
> @@ -381,11 +381,11 @@ static void __init free_unused_memmap(void)
>  				 ALIGN(prev_end, PAGES_PER_SECTION));
>  #else
>  		/*
> -		 * Align down here since the VM subsystem insists that the
> -		 * memmap entries are valid from the bank start aligned to
> -		 * MAX_ORDER_NR_PAGES.
> +		 * Align down here since many operations in VM subsystem
> +		 * presume that there are no holes in the memory map inside
> +		 * a pageblock
>  		 */
> -		start = round_down(start, MAX_ORDER_NR_PAGES);
> +		start = round_down(start, pageblock_nr_pages);
>  #endif
>  		/*
>  		 * If we had a previous bank, and there is a space
> @@ -395,12 +395,12 @@ static void __init free_unused_memmap(void)
>  			free_memmap(prev_end, start);
>  
>  		/*
> -		 * Align up here since the VM subsystem insists that the
> -		 * memmap entries are valid from the bank end aligned to
> -		 * MAX_ORDER_NR_PAGES.
> +		 * Align up here since many operations in VM subsystem
> +		 * presume that there are no holes in the memory map inside
> +		 * a pageblock
>  		 */
>  		prev_end = ALIGN(memblock_region_memory_end_pfn(reg),
> -				 MAX_ORDER_NR_PAGES);
> +				 pageblock_nr_pages);
>  	}
>  
>  #ifdef CONFIG_SPARSEMEM
> -- 
> 2.18.0
> 

-- 
Sincerely yours,
Mike.