Subject: Re: [PATCH 17/21] mm: free_area_init: allow defining max_zone_pfn in descending order

From: Baoquan He <[email-masked]>
Date: Thu, 23 Apr 2020 10:53:11 +0800

On 04/12/20 at 10:48pm, Mike Rapoport wrote:
> From: Mike Rapoport <[email-masked]>
> 
> Some architectures (e.g. ARC) have the ZONE_HIGHMEM zone below the
> ZONE_NORMAL. Allowing free_area_init() parse max_zone_pfn array even it is
> sorted in descending order allows using free_area_init() on such
> architectures.
> 
> Add top -> down traversal of max_zone_pfn array in free_area_init() and use
> the latter in ARC node/zone initialization.

Or maybe leave ARC as is. The change in this patchset doesn't impact
ARC's handling about zone initialization, leaving it as is can reduce
the complication in implementation of free_area_init(), which is a
common function. So I personally don't see a strong motivation to have
this patch.

> 
> Signed-off-by: Mike Rapoport <[email-masked]>
> ---
>  arch/arc/mm/init.c | 36 +++++++-----------------------------
>  mm/page_alloc.c    | 24 +++++++++++++++++++-----
>  2 files changed, 26 insertions(+), 34 deletions(-)
> 
> diff --git a/arch/arc/mm/init.c b/arch/arc/mm/init.c
> index 0920c969c466..41eb9be1653c 100644
> --- a/arch/arc/mm/init.c
> +++ b/arch/arc/mm/init.c
> @@ -63,11 +63,13 @@ void __init early_init_dt_add_memory_arch(u64 base, u64 size)
>  
>  		low_mem_sz = size;
>  		in_use = 1;
> +		memblock_add_node(base, size, 0);
>  	} else {
>  #ifdef CONFIG_HIGHMEM
>  		high_mem_start = base;
>  		high_mem_sz = size;
>  		in_use = 1;
> +		memblock_add_node(base, size, 1);
>  #endif
>  	}
>  
> @@ -83,8 +85,7 @@ void __init early_init_dt_add_memory_arch(u64 base, u64 size)
>   */
>  void __init setup_arch_memory(void)
>  {
> -	unsigned long zones_size[MAX_NR_ZONES];
> -	unsigned long zones_holes[MAX_NR_ZONES];
> +	unsigned long max_zone_pfn[MAX_NR_ZONES] = { 0 };
>  
>  	init_mm.start_code = (unsigned long)_text;
>  	init_mm.end_code = (unsigned long)_etext;
> @@ -115,7 +116,6 @@ void __init setup_arch_memory(void)
>  	 * the crash
>  	 */
>  
> -	memblock_add_node(low_mem_start, low_mem_sz, 0);
>  	memblock_reserve(CONFIG_LINUX_LINK_BASE,
>  			 __pa(_end) - CONFIG_LINUX_LINK_BASE);
>  
> @@ -133,22 +133,7 @@ void __init setup_arch_memory(void)
>  	memblock_dump_all();
>  
>  	/*----------------- node/zones setup --------------------------*/
> -	memset(zones_size, 0, sizeof(zones_size));
> -	memset(zones_holes, 0, sizeof(zones_holes));
> -
> -	zones_size[ZONE_NORMAL] = max_low_pfn - min_low_pfn;
> -	zones_holes[ZONE_NORMAL] = 0;
> -
> -	/*
> -	 * We can't use the helper free_area_init(zones[]) because it uses
> -	 * PAGE_OFFSET to compute the @min_low_pfn which would be wrong
> -	 * when our kernel doesn't start at PAGE_OFFSET, i.e.
> -	 * PAGE_OFFSET != CONFIG_LINUX_RAM_BASE
> -	 */
> -	free_area_init_node(0,			/* node-id */
> -			    zones_size,		/* num pages per zone */
> -			    min_low_pfn,	/* first pfn of node */
> -			    zones_holes);	/* holes */
> +	max_zone_pfn[ZONE_NORMAL] = max_low_pfn;
>  
>  #ifdef CONFIG_HIGHMEM
>  	/*
> @@ -168,20 +153,13 @@ void __init setup_arch_memory(void)
>  	min_high_pfn = PFN_DOWN(high_mem_start);
>  	max_high_pfn = PFN_DOWN(high_mem_start + high_mem_sz);
>  
> -	zones_size[ZONE_NORMAL] = 0;
> -	zones_holes[ZONE_NORMAL] = 0;
> -
> -	zones_size[ZONE_HIGHMEM] = max_high_pfn - min_high_pfn;
> -	zones_holes[ZONE_HIGHMEM] = 0;
> -
> -	free_area_init_node(1,			/* node-id */
> -			    zones_size,		/* num pages per zone */
> -			    min_high_pfn,	/* first pfn of node */
> -			    zones_holes);	/* holes */
> +	max_zone_pfn[ZONE_HIGHMEM] = max_high_pfn;
>  
>  	high_memory = (void *)(min_high_pfn << PAGE_SHIFT);
>  	kmap_init();
>  #endif
> +
> +	free_area_init(max_zone_pfn);
>  }
>  
>  /*
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 343d87b8697d..376434c7a78b 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -7429,7 +7429,8 @@ static void check_for_memory(pg_data_t *pgdat, int nid)
>  void __init free_area_init(unsigned long *max_zone_pfn)
>  {
>  	unsigned long start_pfn, end_pfn;
> -	int i, nid;
> +	int i, nid, zone;
> +	bool descending = false;
>  
>  	/* Record where the zone boundaries are */
>  	memset(arch_zone_lowest_possible_pfn, 0,
> @@ -7439,13 +7440,26 @@ void __init free_area_init(unsigned long *max_zone_pfn)
>  
>  	start_pfn = find_min_pfn_with_active_regions();
>  
> +	/*
> +	 * Some architecturs, e.g. ARC may have ZONE_HIGHMEM below
> +	 * ZONE_NORMAL. For such cases we allow max_zone_pfn sorted in the
> +	 * descending order
> +	 */
> +	if (MAX_NR_ZONES > 1 && max_zone_pfn[0] > max_zone_pfn[1])
> +		descending = true;
> +
>  	for (i = 0; i < MAX_NR_ZONES; i++) {
> -		if (i == ZONE_MOVABLE)
> +		if (descending)
> +			zone = MAX_NR_ZONES - i - 1;
> +		else
> +			zone = i;
> +
> +		if (zone == ZONE_MOVABLE)
>  			continue;
>  
> -		end_pfn = max(max_zone_pfn[i], start_pfn);
> -		arch_zone_lowest_possible_pfn[i] = start_pfn;
> -		arch_zone_highest_possible_pfn[i] = end_pfn;
> +		end_pfn = max(max_zone_pfn[zone], start_pfn);
> +		arch_zone_lowest_possible_pfn[zone] = start_pfn;
> +		arch_zone_highest_possible_pfn[zone] = end_pfn;
>  
>  		start_pfn = end_pfn;
>  	}
> -- 
> 2.25.1
>