Re: [PATCH v27 1/9] memblock: add memblock_cap_memory_range()

[Will Deacon <will.deacon@arm.com>]

On Wed, Nov 02, 2016 at 01:51:53PM +0900, AKASHI Takahiro wrote:
> Add memblock_cap_memory_range() which will remove all the memblock regions
> except the range specified in the arguments.
> 
> This function, like memblock_mem_limit_remove_map(), will not remove
> memblocks with MEMMAP_NOMAP attribute as they may be mapped and accessed
> later as "device memory."
> See the commit a571d4eb55d8 ("mm/memblock.c: add new infrastructure to
> address the mem limit issue").
> 
> This function is used, in a succeeding patch in the series of arm64 kdump
> suuport, to limit the range of usable memory, System RAM, on crash dump
> kernel.
> (Please note that "mem=" parameter is of little use for this purpose.)
> 
> Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
> Cc: linux-mm@kvack.org
> Cc: Andrew Morton <akpm@linux-foundation.org>
> ---
>  include/linux/memblock.h |  1 +
>  mm/memblock.c            | 28 ++++++++++++++++++++++++++++
>  2 files changed, 29 insertions(+)
> 
> diff --git a/include/linux/memblock.h b/include/linux/memblock.h
> index 5b759c9..0e770af 100644
> --- a/include/linux/memblock.h
> +++ b/include/linux/memblock.h
> @@ -334,6 +334,7 @@ phys_addr_t memblock_start_of_DRAM(void);
>  phys_addr_t memblock_end_of_DRAM(void);
>  void memblock_enforce_memory_limit(phys_addr_t memory_limit);
>  void memblock_mem_limit_remove_map(phys_addr_t limit);
> +void memblock_cap_memory_range(phys_addr_t base, phys_addr_t size);
>  bool memblock_is_memory(phys_addr_t addr);
>  int memblock_is_map_memory(phys_addr_t addr);
>  int memblock_is_region_memory(phys_addr_t base, phys_addr_t size);
> diff --git a/mm/memblock.c b/mm/memblock.c
> index 7608bc3..eb53876 100644
> --- a/mm/memblock.c
> +++ b/mm/memblock.c
> @@ -1544,6 +1544,34 @@ void __init memblock_mem_limit_remove_map(phys_addr_t limit)
>  			      (phys_addr_t)ULLONG_MAX);
>  }
>  
> +void __init memblock_cap_memory_range(phys_addr_t base, phys_addr_t size)
> +{
> +	int start_rgn, end_rgn;
> +	int i, ret;
> +
> +	if (!size)
> +		return;
> +
> +	ret = memblock_isolate_range(&memblock.memory, base, size,
> +						&start_rgn, &end_rgn);
> +	if (ret)
> +		return;
> +
> +	/* remove all the MAP regions */
> +	for (i = memblock.memory.cnt - 1; i >= end_rgn; i--)
> +		if (!memblock_is_nomap(&memblock.memory.regions[i]))
> +			memblock_remove_region(&memblock.memory, i);
> +
> +	for (i = start_rgn - 1; i >= 0; i--)
> +		if (!memblock_is_nomap(&memblock.memory.regions[i]))
> +			memblock_remove_region(&memblock.memory, i);
> +
> +	/* truncate the reserved regions */
> +	memblock_remove_range(&memblock.reserved, 0, base);
> +	memblock_remove_range(&memblock.reserved,
> +			base + size, (phys_addr_t)ULLONG_MAX);
> +}

This duplicates a bunch of the logic in memblock_mem_limit_remove_map. Can
you not implement that in terms of your new, more general, function? e.g.
by passing base == 0, and size == limit?

Will

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