linux-kernel - [PATCH 10/14] x86: mm: Enable deferred memory initialisation on x86-64

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Date:	Mon, 13 Apr 2015 11:17:02 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	Linux-MM <linux-mm@...ck.org>
Cc:	Robin Holt <holt@....com>, Nathan Zimmer <nzimmer@....com>,
	Daniel Rahn <drahn@...e.com>,
	Davidlohr Bueso <dbueso@...e.com>,
	Dave Hansen <dave.hansen@...el.com>,
	Tom Vaden <tom.vaden@...com>,
	Scott Norton <scott.norton@...com>,
	LKML <linux-kernel@...r.kernel.org>, Mel Gorman <mgorman@...e.de>
Subject: [PATCH 10/14] x86: mm: Enable deferred memory initialisation on x86-64

This patch adds the Kconfig logic to add deferred memory initialisation
to x86-64 if NUMA is enabled. Other architectures should enable on a
case-by-case basis once the users of early_pfn_to_nid are audited and it
is tested.

Signed-off-by: Mel Gorman <mgorman@...e.de>
---
 arch/x86/Kconfig |  2 ++
 mm/Kconfig       | 19 +++++++++++++++++++
 2 files changed, 21 insertions(+)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index b7d31ca55187..830ad8450bbd 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -32,6 +32,8 @@ config X86
 	select HAVE_UNSTABLE_SCHED_CLOCK
 	select ARCH_SUPPORTS_NUMA_BALANCING if X86_64
 	select ARCH_SUPPORTS_INT128 if X86_64
+	select ARCH_SUPPORTS_DEFERRED_MEM_INIT if X86_64 && NUMA
+	select ARCH_WANTS_PROT_NUMA_PROT_NONE
 	select HAVE_IDE
 	select HAVE_OPROFILE
 	select HAVE_PCSPKR_PLATFORM
diff --git a/mm/Kconfig b/mm/Kconfig
index a03131b6ba8e..463c7005c3d9 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -629,3 +629,22 @@ 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 was to support deferred memory initialisation
+config ARCH_SUPPORTS_DEFERRED_MEM_INIT
+	bool
+
+config DEFERRED_MEM_INIT
+	bool "Defer initialisation of memory to kswapd"
+	default n
+	depends on ARCH_SUPPORTS_DEFERRED_MEM_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 small amount of memory at boot and then initialise the rest when
+	  kswapd starts. Boot times are reduced but very early in the lifetime
+	  of the system it will still be busy initialising struct pages. This
+	  has a potential performance impact on processes until kswapd finishes
+	  the initialisation.
-- 
2.1.2

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