linux-kernel - Re: [PATCH v2] arm64: Expand the static memblock memory table

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Message-ID: <de0788c0-a5a8-cf5b-5f20-eb9e99cd62ca@arm.com>
Date:   Wed, 18 May 2022 10:09:12 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     Zhou Guanghui <zhouguanghui1@...wei.com>,
        akpm@...ux-foundation.org, rppt@...nel.org, will@...nel.org
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-arm-kernel@...ts.infradead.org, xuqiang36@...wei.com
Subject: Re: [PATCH v2] arm64: Expand the static memblock memory table

Hi Zhou,

A small nit.

This changes generic memblock to accommodate arm64 specific scenario.
Keeping the subject line as 'mm/memblock: ...' might be better.

On 5/17/22 17:13, Zhou Guanghui wrote:
> In a system using HBM, a multi-bit ECC error occurs, and the BIOS
> saves the corresponding area (for example, 2 MB). When the system
> restarts next time, these areas are isolated and not reported or
> reported as EFI_UNUSABLE_MEMORY. Both of them lead to an increase

Which cases dont get reported rather than as EFI_UNUSABLE_MEMORY ? Is
this supported on arm64 platform via mainline kernel ?

> in the number of memblocks, whereas EFI_UNUSABLE_MEMORY leads to
> a larger number of memblocks.
> 
> For example, if the EFI_UNUSABLE_MEMORY type is reported:
> ...
> memory[0x92]    [0x0000200834a00000-0x0000200835bfffff], 0x0000000001200000 bytes on node 7 flags: 0x0
> memory[0x93]    [0x0000200835c00000-0x0000200835dfffff], 0x0000000000200000 bytes on node 7 flags: 0x4
> memory[0x94]    [0x0000200835e00000-0x00002008367fffff], 0x0000000000a00000 bytes on node 7 flags: 0x0
> memory[0x95]    [0x0000200836800000-0x00002008369fffff], 0x0000000000200000 bytes on node 7 flags: 0x4
> memory[0x96]    [0x0000200836a00000-0x0000200837bfffff], 0x0000000001200000 bytes on node 7 flags: 0x0
> memory[0x97]    [0x0000200837c00000-0x0000200837dfffff], 0x0000000000200000 bytes on node 7 flags: 0x4
> memory[0x98]    [0x0000200837e00000-0x000020087fffffff], 0x0000000048200000 bytes on node 7 flags: 0x0
> memory[0x99]    [0x0000200880000000-0x0000200bcfffffff], 0x0000000350000000 bytes on node 6 flags: 0x0
> memory[0x9a]    [0x0000200bd0000000-0x0000200bd01fffff], 0x0000000000200000 bytes on node 6 flags: 0x4
> memory[0x9b]    [0x0000200bd0200000-0x0000200bd07fffff], 0x0000000000600000 bytes on node 6 flags: 0x0
> memory[0x9c]    [0x0000200bd0800000-0x0000200bd09fffff], 0x0000000000200000 bytes on node 6 flags: 0x4
> memory[0x9d]    [0x0000200bd0a00000-0x0000200fcfffffff], 0x00000003ff600000 bytes on node 6 flags: 0x0
> memory[0x9e]    [0x0000200fd0000000-0x0000200fd01fffff], 0x0000000000200000 bytes on node 6 flags: 0x4
> memory[0x9f]    [0x0000200fd0200000-0x0000200fffffffff], 0x000000002fe00000 bytes on node 6 flags: 0x0

Got it.

> ...
> 
> If the size of the init memblock regions is exceeded before the
> array size can be resized, the excess memory will be lost.

Could you please elaborate more on why additional memblock regions can
not be accommodated via memblock array resizing ?

> 
> Signed-off-by: Zhou Guanghui <zhouguanghui1@...wei.com>
> ---
>  arch/arm64/include/asm/memory.h |  9 +++++++++
>  mm/memblock.c                   | 14 +++++++++-----
>  2 files changed, 18 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
> index 0af70d9abede..eda61c0389c4 100644
> --- a/arch/arm64/include/asm/memory.h
> +++ b/arch/arm64/include/asm/memory.h
> @@ -364,6 +364,15 @@ void dump_mem_limit(void);
>  # define INIT_MEMBLOCK_RESERVED_REGIONS	(INIT_MEMBLOCK_REGIONS + NR_CPUS + 1)
>  #endif
>  
> +/*
> + * memory regions which marked with flag MEMBLOCK_NOMAP may divide a continuous
> + * memory block into multiple parts. As a result, the number of memory regions
> + * is large.
> + */
> +#ifdef CONFIG_EFI

Could not memblock regions tagged with MEMBLOCK_NOMAP flag not present
on non-EFI systems ? Just wondering, are there not some other scenarios
which will also require expanded static memblock array.

> +#define INIT_MEMBLOCK_MEMORY_REGIONS	1024
> +#endif
> +
>  #include <asm-generic/memory_model.h>
>  
>  #endif /* __ASM_MEMORY_H */
> diff --git a/mm/memblock.c b/mm/memblock.c
> index e4f03a6e8e56..7c63571a69d7 100644
> --- a/mm/memblock.c
> +++ b/mm/memblock.c
> @@ -29,6 +29,10 @@
>  # define INIT_MEMBLOCK_RESERVED_REGIONS		INIT_MEMBLOCK_REGIONS
>  #endif
>  
> +#ifndef INIT_MEMBLOCK_MEMORY_REGIONS
> +#define INIT_MEMBLOCK_MEMORY_REGIONS		INIT_MEMBLOCK_REGIONS
> +#endif

Why create an additional macro INIT_MEMBLOCK_MEMORY_REGIONS ? Why cannot
INIT_MEMBLOCK_REGIONS be defined in the platform directly like the other
macro INIT_MEMBLOCK_RESERVED_REGIONS ?

> +
>  /**
>   * DOC: memblock overview
>   *
> @@ -55,9 +59,9 @@
>   * the allocator metadata. The "memory" and "reserved" types are nicely
>   * wrapped with struct memblock. This structure is statically
>   * initialized at build time. The region arrays are initially sized to
> - * %INIT_MEMBLOCK_REGIONS for "memory" and %INIT_MEMBLOCK_RESERVED_REGIONS
> - * for "reserved". The region array for "physmem" is initially sized to
> - * %INIT_PHYSMEM_REGIONS.
> + * %INIT_MEMBLOCK_MEMORY_REGIONS for "memory" and
> + * %INIT_MEMBLOCK_RESERVED_REGIONS for "reserved". The region array
> + * for "physmem" is initially sized to %INIT_PHYSMEM_REGIONS.
>   * The memblock_allow_resize() enables automatic resizing of the region
>   * arrays during addition of new regions. This feature should be used
>   * with care so that memory allocated for the region array will not
> @@ -102,7 +106,7 @@ unsigned long min_low_pfn;
>  unsigned long max_pfn;
>  unsigned long long max_possible_pfn;
>  
> -static struct memblock_region memblock_memory_init_regions[INIT_MEMBLOCK_REGIONS] __initdata_memblock;
> +static struct memblock_region memblock_memory_init_regions[INIT_MEMBLOCK_MEMORY_REGIONS] __initdata_memblock;
>  static struct memblock_region memblock_reserved_init_regions[INIT_MEMBLOCK_RESERVED_REGIONS] __initdata_memblock;
>  #ifdef CONFIG_HAVE_MEMBLOCK_PHYS_MAP
>  static struct memblock_region memblock_physmem_init_regions[INIT_PHYSMEM_REGIONS];
> @@ -111,7 +115,7 @@ static struct memblock_region memblock_physmem_init_regions[INIT_PHYSMEM_REGIONS
>  struct memblock memblock __initdata_memblock = {
>  	.memory.regions		= memblock_memory_init_regions,
>  	.memory.cnt		= 1,	/* empty dummy entry */
> -	.memory.max		= INIT_MEMBLOCK_REGIONS,
> +	.memory.max		= INIT_MEMBLOCK_MEMORY_REGIONS,
>  	.memory.name		= "memory",
>  
>  	.reserved.regions	= memblock_reserved_init_regions,

- Anshuman