Re: [PATCH 04/11] Allow CONFIG_MIGRATION to be set without CONFIG_NUMA or memory hot-remove

[KOSAKI Motohiro]

> CONFIG_MIGRATION currently depends on CONFIG_NUMA or on the architecture
> being able to hot-remove memory. The main users of page migration such as
> sys_move_pages(), sys_migrate_pages() and cpuset process migration are
> only beneficial on NUMA so it makes sense.
> 
> As memory compaction will operate within a zone and is useful on both NUMA
> and non-NUMA systems, this patch allows CONFIG_MIGRATION to be set if the
> user selects CONFIG_COMPACTION as an option.
> 
> Signed-off-by: Mel Gorman <mel@xxxxxxxxx>
> Reviewed-by: Christoph Lameter <cl@xxxxxxxxxxxxxxxxxxxx>
> Reviewed-by: Rik van Riel <riel@xxxxxxxxxx>
> Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
> ---
>  mm/Kconfig |   20 ++++++++++++++++----
>  1 files changed, 16 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/Kconfig b/mm/Kconfig
> index 9c61158..04e241b 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -172,17 +172,29 @@ config SPLIT_PTLOCK_CPUS
>  	default "4"
>  
>  #
> +# support for memory compaction
> +config COMPACTION
> +	bool "Allow for memory compaction"
> +	def_bool y
> +	select MIGRATION
> +	depends on EXPERIMENTAL && HUGETLBFS && MMU
> +	help
> +	  Allows the compaction of memory for the allocation of huge pages.
> +

If select MIGRATION works, we can remove "depends on NUMA || ARCH_ENABLE_MEMORY_HOTREMOVE"
line from config MIGRATION.



> +#
>  # support for page migration
>  #
>  config MIGRATION
>  	bool "Page migration"
>  	def_bool y
> -	depends on NUMA || ARCH_ENABLE_MEMORY_HOTREMOVE
> +	depends on NUMA || ARCH_ENABLE_MEMORY_HOTREMOVE || COMPACTION
>  	help
>  	  Allows the migration of the physical location of pages of processes
> -	  while the virtual addresses are not changed. This is useful for
> -	  example on NUMA systems to put pages nearer to the processors accessing
> -	  the page.
> +	  while the virtual addresses are not changed. This is useful in
> +	  two situations. The first is on NUMA systems to put pages nearer
> +	  to the processors accessing. The second is when allocating huge
> +	  pages as migration can relocate pages to satisfy a huge page
> +	  allocation instead of reclaiming.
>  
>  config PHYS_ADDR_T_64BIT
>  	def_bool 64BIT || ARCH_PHYS_ADDR_T_64BIT
> -- 
> 1.6.5
> 



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