mm: meminit: initialise a subset of struct pages if CONFIG_DEFERRED_STRUCT_PAGE_INIT is set

This patch initalises all low memory struct pages and 2G of the highest
zone on each node during memory initialisation if
CONFIG_DEFERRED_STRUCT_PAGE_INIT is set.  That config option cannot be set
but will be available in a later patch.  Parallel initialisation of struct
page depends on some features from memory hotplug and it is necessary to
alter alter section annotations.

Signed-off-by: Mel Gorman <mgorman@suse.de>
Tested-by: Nate Zimmer <nzimmer@sgi.com>
Tested-by: Waiman Long <waiman.long@hp.com>
Tested-by: Daniel J Blueman <daniel@numascale.com>
Acked-by: Pekka Enberg <penberg@kernel.org>
Cc: Robin Holt <robinmholt@gmail.com>
Cc: Nate Zimmer <nzimmer@sgi.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Waiman Long <waiman.long@hp.com>
Cc: Scott Norton <scott.norton@hp.com>
Cc: "Luck, Tony" <tony.luck@intel.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 18 insertions, 0 deletions

diff --git a/mm/Kconfig b/mm/Kconfig
index c180af880ed5..e79de2bd12cd 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -636,3 +636,21 @@ config MAX_STACK_SIZE_MB
           changed to a smaller value in which case that is used.
 
           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 kswapd"
+        default n
+        depends on ARCH_SUPPORTS_DEFERRED_STRUCT_PAGE_INIT
+        depends on MEMORY_HOTPLUG
+        help
+          Ordinarily all struct pages are initialised during early boot in a
+          single thread. On very large machines this can take a considerable
+          amount of time. If this option is set, large machines will bring up
+          a subset of memmap at boot and then initialise the rest in parallel
+          when kswapd starts. This has a potential performance impact on
+          processes running early in the lifetime of the systemm until kswapd
+          finishes the initialisation.