Re: [PATCH v1] mm: relax deferred struct page requirements

[Michal Hocko]

On Thu 16-11-17 20:46:01, Pavel Tatashin wrote:
> There is no need to have ARCH_SUPPORTS_DEFERRED_STRUCT_PAGE_INIT,
> as all the page initialization code is in common code.
> 
> Also, there is no need to depend on MEMORY_HOTPLUG, as initialization code
> does not really use hotplug memory functionality. So, we can remove this
> requirement as well.
> 
> This patch allows to use deferred struct page initialization on all
> platforms with memblock allocator.
> 
> Tested on x86, arm64, and sparc. Also, verified that code compiles on
> PPC with CONFIG_MEMORY_HOTPLUG disabled.

There is slight risk that we will encounter corner cases on some
architectures with weird memory layout/topology but we should better
explicitly disable this code rather than make it opt-in so this looks
like an improvement to me.
 
> Signed-off-by: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>

Acked-by: Michal Hocko <mhocko@xxxxxxxx>

> ---
>  arch/powerpc/Kconfig | 1 -
>  arch/s390/Kconfig    | 1 -
>  arch/x86/Kconfig     | 1 -
>  mm/Kconfig           | 7 +------
>  4 files changed, 1 insertion(+), 9 deletions(-)
> 
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index cb782ac1c35d..1540348691c9 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -148,7 +148,6 @@ config PPC
>  	select ARCH_MIGHT_HAVE_PC_PARPORT
>  	select ARCH_MIGHT_HAVE_PC_SERIO
>  	select ARCH_SUPPORTS_ATOMIC_RMW
> -	select ARCH_SUPPORTS_DEFERRED_STRUCT_PAGE_INIT
>  	select ARCH_USE_BUILTIN_BSWAP
>  	select ARCH_USE_CMPXCHG_LOCKREF		if PPC64
>  	select ARCH_WANT_IPC_PARSE_VERSION
> diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
> index 863a62a6de3c..525c2e3df6f5 100644
> --- a/arch/s390/Kconfig
> +++ b/arch/s390/Kconfig
> @@ -108,7 +108,6 @@ config S390
>  	select ARCH_INLINE_WRITE_UNLOCK_IRQRESTORE
>  	select ARCH_SAVE_PAGE_KEYS if HIBERNATION
>  	select ARCH_SUPPORTS_ATOMIC_RMW
> -	select ARCH_SUPPORTS_DEFERRED_STRUCT_PAGE_INIT
>  	select ARCH_SUPPORTS_NUMA_BALANCING
>  	select ARCH_USE_BUILTIN_BSWAP
>  	select ARCH_USE_CMPXCHG_LOCKREF
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index df3276d6bfe3..00a5446de394 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -69,7 +69,6 @@ config X86
>  	select ARCH_MIGHT_HAVE_PC_PARPORT
>  	select ARCH_MIGHT_HAVE_PC_SERIO
>  	select ARCH_SUPPORTS_ATOMIC_RMW
> -	select ARCH_SUPPORTS_DEFERRED_STRUCT_PAGE_INIT
>  	select ARCH_SUPPORTS_NUMA_BALANCING	if X86_64
>  	select ARCH_USE_BUILTIN_BSWAP
>  	select ARCH_USE_QUEUED_RWLOCKS
> diff --git a/mm/Kconfig b/mm/Kconfig
> index 9c4bdddd80c2..c6bd0309ce7a 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -639,15 +639,10 @@ config MAX_STACK_SIZE_MB
>  
>  	  A sane initial value is 80 MB.
>  
> -# For architectures that support deferred memory initialisation
> -config ARCH_SUPPORTS_DEFERRED_STRUCT_PAGE_INIT
> -	bool
> -
>  config DEFERRED_STRUCT_PAGE_INIT
>  	bool "Defer initialisation of struct pages to kthreads"
>  	default n
> -	depends on ARCH_SUPPORTS_DEFERRED_STRUCT_PAGE_INIT
> -	depends on NO_BOOTMEM && MEMORY_HOTPLUG
> +	depends on NO_BOOTMEM
>  	depends on !FLATMEM
>  	help
>  	  Ordinarily all struct pages are initialised during early boot in a
> -- 
> 2.15.0

-- 
Michal Hocko
SUSE Labs