From 8b368e8e961944105945fbe36f3f264252bfd19a Mon Sep 17 00:00:00 2001

From: Dan Williams <dan.j.williams@intel.com>

Date: Thu, 25 Feb 2016 01:02:30 +0000

Subject: [PATCH] mm: CONFIG_NR_ZONES_EXTENDED

ZONE_DEVICE (merged in 4.3) and ZONE_CMA (proposed) are examples of new mm

zones that are bumping up against the current maximum limit of 4 zones,

i.e.  2 bits in page->flags.  When adding a zone this equation still needs

to be satisified:

    SECTIONS_WIDTH + ZONES_WIDTH + NODES_SHIFT + LAST_CPUPID_SHIFT

	  <= BITS_PER_LONG - NR_PAGEFLAGS

ZONE_DEVICE currently tries to satisfy this equation by requiring that

ZONE_DMA be disabled, but this is untenable given generic kernels want to

support ZONE_DEVICE and ZONE_DMA simultaneously.  ZONE_CMA would like to

increase the amount of memory covered per section, but that limits the

minimum granularity at which consecutive memory ranges can be added via

devm_memremap_pages().

The trade-off of what is acceptable to sacrifice depends heavily on the

platform.  For example, ZONE_CMA is targeted for 32-bit platforms where

page->flags is constrained, but those platforms likely do not care about

the minimum granularity of memory hotplug.  A big iron machine with 1024

numa nodes can likely sacrifice ZONE_DMA where a general purpose

distribution kernel can not.

CONFIG_NR_ZONES_EXTENDED is a configuration symbol that gets selected when

the number of configured zones exceeds 4.  It documents the configuration

symbols and definitions that get modified when ZONES_WIDTH is greater than

2.

For now, it steals a bit from NODES_SHIFT.  Later on it can be used to

document the definitions that get modified when a 32-bit configuration

wants more zone bits.

Note that GFP_ZONE_TABLE poses an interesting constraint since

include/linux/gfp.h gets included by the 32-bit portion of a 64-bit build.

We need to be careful to only build the table for zones that have a

corresponding gfp_t flag.  GFP_ZONES_SHIFT is introduced for this purpose.

This patch does not attempt to solve the problem of adding a new zone

that also has a corresponding GFP_ flag.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=110931

Fixes: 033fbae988fc ("mm: ZONE_DEVICE for "device memory"")

Signed-off-by: Dan Williams <dan.j.williams@intel.com>

Reported-by: Mark <markk@clara.co.uk>

Cc: Mel Gorman <mgorman@suse.de>

Cc: Rik van Riel <riel@redhat.com>

Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>

Cc: Dave Hansen <dave.hansen@linux.intel.com>

Cc: Sudip Mukherjee <sudipm.mukherjee@gmail.com>

Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

---

 arch/x86/Kconfig                  |  6 ++++--

 include/linux/gfp.h               | 33 ++++++++++++++++++++-------------

 include/linux/page-flags-layout.h |  2 ++

 mm/Kconfig                        |  7 +++++--

 4 files changed, 31 insertions(+), 17 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig

index 3fef519..b94704a 100644

--- a/arch/x86/Kconfig

+++ b/arch/x86/Kconfig

@@ -1409,8 +1409,10 @@ config NUMA_EMU

 config NODES_SHIFT

 	int "Maximum NUMA Nodes (as a power of 2)" if !MAXSMP

-	range 1 10

-	default "10" if MAXSMP

+	range 1 10 if !NR_ZONES_EXTENDED

+	range 1 9 if NR_ZONES_EXTENDED

+	default "10" if MAXSMP && !NR_ZONES_EXTENDED

+	default "9" if MAXSMP && NR_ZONES_EXTENDED

 	default "6" if X86_64

 	default "3"

 	depends on NEED_MULTIPLE_NODES

diff --git a/include/linux/gfp.h b/include/linux/gfp.h

index af1f2b2..d201d8a 100644

--- a/include/linux/gfp.h

+++ b/include/linux/gfp.h

@@ -329,22 +329,29 @@ static inline bool gfpflags_allow_blocking(const gfp_t gfp_flags)

  *       0xe    => BAD (MOVABLE+DMA32+HIGHMEM)

  *       0xf    => BAD (MOVABLE+DMA32+HIGHMEM+DMA)

  *

- * ZONES_SHIFT must be <= 2 on 32 bit platforms.

+ * GFP_ZONES_SHIFT must be <= 2 on 32 bit platforms.

  */

-#if 16 * ZONES_SHIFT > BITS_PER_LONG

-#error ZONES_SHIFT too large to create GFP_ZONE_TABLE integer

+#if defined(CONFIG_ZONE_DEVICE) && (MAX_NR_ZONES-1) <= 4

+/* ZONE_DEVICE is not a valid GFP zone specifier */

+#define GFP_ZONES_SHIFT 2

+#else

+#define GFP_ZONES_SHIFT ZONES_SHIFT

+#endif

+

+#if 16 * GFP_ZONES_SHIFT > BITS_PER_LONG

+#error GFP_ZONES_SHIFT too large to create GFP_ZONE_TABLE integer

 #endif

 #define GFP_ZONE_TABLE ( \

-	(ZONE_NORMAL << 0 * ZONES_SHIFT)				      \

-	| (OPT_ZONE_DMA << ___GFP_DMA * ZONES_SHIFT)			      \

-	| (OPT_ZONE_HIGHMEM << ___GFP_HIGHMEM * ZONES_SHIFT)		      \

-	| (OPT_ZONE_DMA32 << ___GFP_DMA32 * ZONES_SHIFT)		      \

-	| (ZONE_NORMAL << ___GFP_MOVABLE * ZONES_SHIFT)			      \

-	| (OPT_ZONE_DMA << (___GFP_MOVABLE | ___GFP_DMA) * ZONES_SHIFT)	      \

-	| (ZONE_MOVABLE << (___GFP_MOVABLE | ___GFP_HIGHMEM) * ZONES_SHIFT)   \

-	| (OPT_ZONE_DMA32 << (___GFP_MOVABLE | ___GFP_DMA32) * ZONES_SHIFT)   \

+	(ZONE_NORMAL << 0 * GFP_ZONES_SHIFT)					\

+	| (OPT_ZONE_DMA << ___GFP_DMA * GFP_ZONES_SHIFT)			\

+	| (OPT_ZONE_HIGHMEM << ___GFP_HIGHMEM * GFP_ZONES_SHIFT)		\

+	| (OPT_ZONE_DMA32 << ___GFP_DMA32 * GFP_ZONES_SHIFT)		      	\

+	| (ZONE_NORMAL << ___GFP_MOVABLE * GFP_ZONES_SHIFT)			\

+	| (OPT_ZONE_DMA << (___GFP_MOVABLE | ___GFP_DMA) * GFP_ZONES_SHIFT)	\

+	| (ZONE_MOVABLE << (___GFP_MOVABLE | ___GFP_HIGHMEM) * GFP_ZONES_SHIFT)	\

+	| (OPT_ZONE_DMA32 << (___GFP_MOVABLE | ___GFP_DMA32) * GFP_ZONES_SHIFT)	\

 )

 /*

@@ -369,8 +376,8 @@ static inline enum zone_type gfp_zone(gfp_t flags)

 	enum zone_type z;

 	int bit = (__force int) (flags & GFP_ZONEMASK);

-	z = (GFP_ZONE_TABLE >> (bit * ZONES_SHIFT)) &

-					 ((1 << ZONES_SHIFT) - 1);

+	z = (GFP_ZONE_TABLE >> (bit * GFP_ZONES_SHIFT)) &

+					 ((1 << GFP_ZONES_SHIFT) - 1);

 	VM_BUG_ON((GFP_ZONE_BAD >> bit) & 1);

 	return z;

 }

diff --git a/include/linux/page-flags-layout.h b/include/linux/page-flags-layout.h

index da52366..77b078c 100644

--- a/include/linux/page-flags-layout.h

+++ b/include/linux/page-flags-layout.h

@@ -17,6 +17,8 @@

 #define ZONES_SHIFT 1

 #elif MAX_NR_ZONES <= 4

 #define ZONES_SHIFT 2

+#elif MAX_NR_ZONES <= 8

+#define ZONES_SHIFT 3

 #else

 #error ZONES_SHIFT -- too many zones configured adjust calculation

 #endif

diff --git a/mm/Kconfig b/mm/Kconfig

index 031a329..7826216 100644

--- a/mm/Kconfig

+++ b/mm/Kconfig

@@ -652,8 +652,6 @@ config IDLE_PAGE_TRACKING

 config ZONE_DEVICE

 	bool "Device memory (pmem, etc...) hotplug support"

-	default !ZONE_DMA

-	depends on !ZONE_DMA

 	depends on MEMORY_HOTPLUG

 	depends on MEMORY_HOTREMOVE

 	depends on X86_64 #arch_add_memory() comprehends device memory

@@ -667,5 +665,10 @@ config ZONE_DEVICE

 	  If FS_DAX is enabled, then say Y.

+config NR_ZONES_EXTENDED

+	bool

+	default n if !64BIT

+	default y if ZONE_DEVICE && ZONE_DMA && ZONE_DMA32

+

 config FRAME_VECTOR

 	bool

-- 

2.5.0