Re: [PATCH V2] mm: Generalize HUGETLB_PAGE_SIZE_VARIABLE

[Anshuman Khandual <anshuman.khandual@arm.com>]

On 3/2/21 10:43 AM, Anshuman Khandual wrote:
> HUGETLB_PAGE_SIZE_VARIABLE need not be defined for each individual
> platform subscribing it. Instead just make it generic.
> 
> Cc: Michael Ellerman <mpe@ellerman.id.au>
> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> Cc: Paul Mackerras <paulus@samba.org>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: linux-ia64@vger.kernel.org
> Cc: linuxppc-dev@lists.ozlabs.org
> Cc: linux-mm@kvack.org
> Cc: linux-kernel@vger.kernel.org
> Suggested-by: Christoph Hellwig <hch@lst.de>
> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
> ---
> This change was originally suggested in an earilier discussion. This
> applies on v5.12-rc1 and has been build tested on all applicable
> platforms i.e ia64 and powerpc.
> 
> https://patchwork.kernel.org/project/linux-mm/patch/1613024531-19040-3-git-send-email-anshuman.khandual@arm.com/
> 
> Changes in V2:
> 
> - Added a description for HUGETLB_PAGE_SIZE_VARIABLE
> - Added HUGETLB_PAGE dependency while selecting HUGETLB_PAGE_SIZE_VARIABLE
> 
> Changes in V1:
> 
> https://patchwork.kernel.org/project/linux-mm/patch/1614577853-7452-1-git-send-email-anshuman.khandual@arm.com/
> 
>  arch/ia64/Kconfig    | 6 +-----
>  arch/powerpc/Kconfig | 6 +-----
>  mm/Kconfig           | 9 +++++++++
>  3 files changed, 11 insertions(+), 10 deletions(-)
> 
> diff --git a/arch/ia64/Kconfig b/arch/ia64/Kconfig
> index 2ad7a8d29fcc..dccf5bfebf48 100644
> --- a/arch/ia64/Kconfig
> +++ b/arch/ia64/Kconfig
> @@ -32,6 +32,7 @@ config IA64
>  	select TTY
>  	select HAVE_ARCH_TRACEHOOK
>  	select HAVE_VIRT_CPU_ACCOUNTING
> +	select HUGETLB_PAGE_SIZE_VARIABLE if HUGETLB_PAGE
>  	select VIRT_TO_BUS
>  	select GENERIC_IRQ_PROBE
>  	select GENERIC_PENDING_IRQ if SMP
> @@ -82,11 +83,6 @@ config STACKTRACE_SUPPORT
>  config GENERIC_LOCKBREAK
>  	def_bool n
>  
> -config HUGETLB_PAGE_SIZE_VARIABLE
> -	bool
> -	depends on HUGETLB_PAGE
> -	default y
> -
>  config GENERIC_CALIBRATE_DELAY
>  	bool
>  	default y
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index 3778ad17f56a..3fdec3e53256 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -232,6 +232,7 @@ config PPC
>  	select HAVE_HARDLOCKUP_DETECTOR_PERF	if PERF_EVENTS && HAVE_PERF_EVENTS_NMI && !HAVE_HARDLOCKUP_DETECTOR_ARCH
>  	select HAVE_PERF_REGS
>  	select HAVE_PERF_USER_STACK_DUMP
> +	select HUGETLB_PAGE_SIZE_VARIABLE	if PPC_BOOK3S_64 && HUGETLB_PAGE
>  	select MMU_GATHER_RCU_TABLE_FREE
>  	select MMU_GATHER_PAGE_SIZE
>  	select HAVE_REGS_AND_STACK_ACCESS_API
> @@ -416,11 +417,6 @@ config HIGHMEM
>  
>  source "kernel/Kconfig.hz"
>  
> -config HUGETLB_PAGE_SIZE_VARIABLE
> -	bool
> -	depends on HUGETLB_PAGE && PPC_BOOK3S_64
> -	default y
> -
>  config MATH_EMULATION
>  	bool "Math emulation"
>  	depends on 4xx || PPC_8xx || PPC_MPC832x || BOOKE
> diff --git a/mm/Kconfig b/mm/Kconfig
> index 24c045b24b95..64f1e0503e4f 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -274,6 +274,15 @@ config ARCH_ENABLE_HUGEPAGE_MIGRATION
>  config ARCH_ENABLE_THP_MIGRATION
>  	bool
>  
> +config HUGETLB_PAGE_SIZE_VARIABLE
> +	bool "Allows dynamic pageblock_order"
> +	def_bool n
> +	depends on HUGETLB_PAGE

Seems like this dependency on HUGETLB_PAGE is redundant, as it is
already being ensured on the platforms while selecting the config.

> +	help
> +	  Allows the pageblock_order value to be dynamic instead of just standard
> +	  HUGETLB_PAGE_ORDER when there are multiple HugeTLB page sizes available
> +	  on a platform.
> +
>  config CONTIG_ALLOC
>  	def_bool (MEMORY_ISOLATION && COMPACTION) || CMA
>  
>