mm: relax deferred struct page requirements

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.

Link: http:https://lkml.kernel.org/r/[email protected]
Signed-off-by: Pavel Tatashin <[email protected]>
Acked-by: Heiko Carstens <[email protected]>	[s390]
Reviewed-by: Khalid Aziz <[email protected]>
Acked-by: Michael Ellerman <[email protected]>
Acked-by: Michal Hocko <[email protected]>
Cc: Steven Sistare <[email protected]>
Cc: Daniel Jordan <[email protected]>
Cc: Benjamin Herrenschmidt <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Kirill A. Shutemov <[email protected]>
Cc: Reza Arbab <[email protected]>
Cc: Martin Schwidefsky <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Mel Gorman <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

arch/powerpc/Kconfig

@@ -151,7 +151,6 @@ 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

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

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

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