[PATCH 0/8] Optional ZONE_DMA V2

[PATCH 0/8] Optional ZONE_DMA V2

[Christoph Lameter]

Optional ZONE_DMA V2

V1->V2
- Sh sh64 and parisc do not need ZONE_DMA so do not define
  CONFIG_ZONE_DMA for those zones. Add patches for those
  arches to remove the use of ZONE_DMA (untested since
  I do not have those arches).
- Update documentation after feedback from V1.

This patch follows up on the earlier work in Andrew's tree to reduce
the number of zones. The patches allow to go to a minimum of 2 zones.
This one allows also to make ZONE_DMA optional and therefore the
number of zones can be reduced to one.

ZONE_DMA is usually used for ISA DMA devices. There are a number
of reasons why we would not want to have ZONE_DMA

1. Some arches do not need ZONE_DMA at all.

2. With the advent of IOMMUs DMA zones are no longer needed.
   The necessity of DMA zones may drastically be reduced
   in the future. This patchset allows a compilation of
   a kernel without that overhead.

3. Devices that require ISA DMA get rare these days. All
   my systems do not have any need for ISA DMA.

4. The presence of an additional zone unecessarily complicates
   VM operations because it must be scanned and balancing
   logic must operate on its.

5. With only ZONE_NORMAL one can reach the situation where
   we have only one zone. This will allow the unrolling of many
   loops in the VM and allows the optimization of varous
   code paths in the VM.

6. Having only a single zone in a NUMA system results in a
   1-1 correspondence between nodes and zones. Various additional
   optimizations to critical VM paths become possible.

Many systems today can operate just fine with a single zone.
If you look at what is in ZONE_DMA then one usually sees that nothing
uses it. The DMA slabs are empty (Some arches use ZONE_DMA instead
of ZONE_NORMAL, then ZONE_NORMAL will be empty instead).

On all of my systems (i386, x86_64, ia64) ZONE_DMA is completely empty.
Why constantly look at an empty zone in /proc/zoneinfo and empty slab
in /proc/slabinfo?  Non i386 also frequently have no need for ZONE_DMA
and zones stay empty.

The patchset was tested on i386 (UP / SMP), x86_64 (UP, NUMA) and
ia64 (NUMA).

The RFC posted earlier (see
http://marc.theaimsgroup.com/?l=linux-kernel&m=115231723513008&w=2)
had lots of #ifdefs in them. An effort has been made to minize the number
of #ifdefs and make this as compact as possible. The job was made much easier
by the ongoing efforts of others to extract common arch specific functionality.

I have been running this for awhile now on my desktop and finally Linux is
using all my available RAM instead of leaving the 16MB in ZONE_DMA untouched:

christoph@pentium940:~$ cat /proc/zoneinfo
Node 0, zone   Normal
  pages free     4435
        min      1448
        low      1810
        high     2172
        active   241786
        inactive 210170
        scanned  0 (a: 0 i: 0)
        spanned  524224
        present  524224
    nr_anon_pages 61680
    nr_mapped    14271
    nr_file_pages 390264
    nr_slab_reclaimable 27564
    nr_slab_unreclaimable 1793
    nr_page_table_pages 449
    nr_dirty     39
    nr_writeback 0
    nr_unstable  0
    nr_bounce    0
    cpu: 0 pcp: 0
              count: 156
              high:  186
              batch: 31
    cpu: 0 pcp: 1
              count: 9
              high:  62
              batch: 15
  vm stats threshold: 20
    cpu: 1 pcp: 0
              count: 177
              high:  186
              batch: 31
    cpu: 1 pcp: 1
              count: 12
              high:  62
              batch: 15
  vm stats threshold: 20
  all_unreclaimable: 0
  prev_priority:     12
  temp_priority:     12
  start_pfn:         0

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[PATCH 1/8] Deal with cases of ZONE_DMA meaning the first zone

[Christoph Lameter]

Optional DMA zone: Replace uses of ZONE_DMA as the first zone

In two places in the VM we use ZONE_DMA to refer to the first zone.
If ZONE_DMA is optional then other zones may be first. So simply
replace ZONE_DMA with zone 0.

This also fixes ZONETABLE_PGSHIFT. If we have only a single zone then
ZONES_PGSHIFT may become 0 because there is no need anymore to encode the
zone number related to a pgdat. However, we still need a zonetable to index
all the zones for each node if this is a NUMA system. Therefore define
ZONETABLE_SHIFT unconditionally as the offset of the ZONE field in page flags.

Acked-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Christoph Lameter <clameter@sgi.com>

Index: linux-2.6.18-rc6-mm2/mm/mempolicy.c
===================================================================
--- linux-2.6.18-rc6-mm2.orig/mm/mempolicy.c	2006-09-18 13:07:53.318935179 -0500
+++ linux-2.6.18-rc6-mm2/mm/mempolicy.c	2006-09-18 13:16:18.929008279 -0500
@@ -105,7 +105,7 @@ static struct kmem_cache *sn_cache;
 
 /* Highest zone. An specific allocation for a zone below that is not
    policied. */
-enum zone_type policy_zone = ZONE_DMA;
+enum zone_type policy_zone = 0;
 
 struct mempolicy default_policy = {
 	.refcnt = ATOMIC_INIT(1), /* never free it */
Index: linux-2.6.18-rc6-mm2/mm/page_alloc.c
===================================================================
--- linux-2.6.18-rc6-mm2.orig/mm/page_alloc.c	2006-09-18 13:16:14.463795639 -0500
+++ linux-2.6.18-rc6-mm2/mm/page_alloc.c	2006-09-18 13:27:53.271625765 -0500
@@ -2486,11 +2486,11 @@ static void __meminit free_area_init_cor
 				"  %s zone: %lu pages exceeds realsize %lu\n",
 				zone_names[j], memmap_pages, realsize);
 
-		/* Account for reserved DMA pages */
-		if (j == ZONE_DMA && realsize > dma_reserve) {
+		/* Account for reserved pages */
+		if (j == 0 && realsize > dma_reserve) {
 			realsize -= dma_reserve;
-			printk(KERN_DEBUG "  DMA zone: %lu pages reserved\n",
-								dma_reserve);
+			printk(KERN_DEBUG "  %s zone: %lu pages reserved\n",
+					zone_names[0], dma_reserve);
 		}
 
 		if (!is_highmem_idx(j))
Index: linux-2.6.18-rc6-mm2/include/linux/mm.h
===================================================================
--- linux-2.6.18-rc6-mm2.orig/include/linux/mm.h	2006-09-18 13:16:14.000000000 -0500
+++ linux-2.6.18-rc6-mm2/include/linux/mm.h	2006-09-18 13:28:52.406396556 -0500
@@ -416,7 +416,7 @@ void split_page(struct page *page, unsig
 #else
 #define ZONETABLE_SHIFT		(SECTIONS_SHIFT + ZONES_SHIFT)
 #endif
-#define ZONETABLE_PGSHIFT	ZONES_PGSHIFT
+#define ZONETABLE_PGSHIFT	ZONES_PGOFF
 
 #if SECTIONS_WIDTH+NODES_WIDTH+ZONES_WIDTH > FLAGS_RESERVED
 #error SECTIONS_WIDTH+NODES_WIDTH+ZONES_WIDTH > FLAGS_RESERVED

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[PATCH 2/8] Introduce CONFIG_ZONE_DMA

[Christoph Lameter]

Introduce CONFIG_ZONE_DMA

This patch simply defines CONFIG_ZONE_DMA for all arches. We later do
special things with CONFIG_ZONE_DMA after the VM and an arch are
prepared to work without ZONE_DMA.

CONFIG_ZONE_DMA can be defined in two ways depending on how
an architecture handles ISA DMA.

First if CONFIG_GENERIC_ISA_DMA is set by the arch then we know that
the arch needs ZONE_DMA because ISA DMA devices are supported. We
can catch this in mm/Kconfig and do not need to modify arch code.

Second, arches may use ZONE_DMA in an unknown way. We set CONFIG_ZONE_DMA
for all arches that do not set CONFIG_GENERIC_ISA_DMA in order to insure
backwards compatibility. The arches may later undefine ZONE_DMA
if their arch code has been verified to not depend on ZONE_DMA.

Signed-off-by: Christoph Lameter <clameter@sgi.com>

Index: linux-2.6.18-rc6-mm2/mm/Kconfig
===================================================================
--- linux-2.6.18-rc6-mm2.orig/mm/Kconfig	2006-09-15 12:17:39.778004366 -0500
+++ linux-2.6.18-rc6-mm2/mm/Kconfig	2006-09-18 12:27:12.303278031 -0500
@@ -139,6 +139,10 @@ config SPLIT_PTLOCK_CPUS
 	default "4096" if PARISC && !PA20
 	default "4"
 
+config ZONE_DMA
+	def_bool y
+	depends on GENERIC_ISA_DMA
+
 #
 # support for page migration
 #
Index: linux-2.6.18-rc6-mm2/arch/ia64/Kconfig
===================================================================
--- linux-2.6.18-rc6-mm2.orig/arch/ia64/Kconfig	2006-09-15 12:17:39.786794169 -0500
+++ linux-2.6.18-rc6-mm2/arch/ia64/Kconfig	2006-09-18 12:27:12.361876548 -0500
@@ -22,6 +22,10 @@ config 64BIT
 	bool
 	default y
 
+config ZONE_DMA
+	bool
+	default y
+
 config MMU
 	bool
 	default y
Index: linux-2.6.18-rc6-mm2/arch/cris/Kconfig
===================================================================
--- linux-2.6.18-rc6-mm2.orig/arch/cris/Kconfig	2006-09-15 12:17:39.795583972 -0500
+++ linux-2.6.18-rc6-mm2/arch/cris/Kconfig	2006-09-18 12:27:12.388245880 -0500
@@ -9,6 +9,10 @@ config MMU
 	bool
 	default y
 
+config ZONE_DMA
+	bool
+	default y
+
 config RWSEM_GENERIC_SPINLOCK
 	bool
 	default y
Index: linux-2.6.18-rc6-mm2/arch/s390/Kconfig
===================================================================
--- linux-2.6.18-rc6-mm2.orig/arch/s390/Kconfig	2006-09-15 12:17:39.804373775 -0500
+++ linux-2.6.18-rc6-mm2/arch/s390/Kconfig	2006-09-18 12:27:12.426334916 -0500
@@ -7,6 +7,10 @@ config MMU
 	bool
 	default y
 
+config ZONE_DMA
+	bool
+	default y
+
 config LOCKDEP_SUPPORT
 	bool
 	default y
Index: linux-2.6.18-rc6-mm2/arch/xtensa/Kconfig
===================================================================
--- linux-2.6.18-rc6-mm2.orig/arch/xtensa/Kconfig	2006-09-15 12:17:39.813163578 -0500
+++ linux-2.6.18-rc6-mm2/arch/xtensa/Kconfig	2006-09-18 12:27:12.459540742 -0500
@@ -7,6 +7,10 @@ config FRAME_POINTER
 	bool
 	default n
 
+config ZONE_DMA
+	bool
+	default y
+
 config XTENSA
 	bool
 	default y
Index: linux-2.6.18-rc6-mm2/arch/h8300/Kconfig
===================================================================
--- linux-2.6.18-rc6-mm2.orig/arch/h8300/Kconfig	2006-09-15 12:17:39.820976736 -0500
+++ linux-2.6.18-rc6-mm2/arch/h8300/Kconfig	2006-09-18 12:27:12.496653135 -0500
@@ -17,6 +17,10 @@ config SWAP
 	bool
 	default n
 
+config ZONE_DMA
+	bool
+	default y
+
 config FPU
 	bool
 	default n
Index: linux-2.6.18-rc6-mm2/arch/v850/Kconfig
===================================================================
--- linux-2.6.18-rc6-mm2.orig/arch/v850/Kconfig	2006-09-15 12:17:39.830743184 -0500
+++ linux-2.6.18-rc6-mm2/arch/v850/Kconfig	2006-09-18 12:27:12.524975752 -0500
@@ -10,6 +10,9 @@ mainmenu "uClinux/v850 (w/o MMU) Kernel 
 config MMU
        	bool
 	default n
+config ZONE_DMA
+	bool
+	default y
 config RWSEM_GENERIC_SPINLOCK
 	bool
 	default y
Index: linux-2.6.18-rc6-mm2/arch/frv/Kconfig
===================================================================
--- linux-2.6.18-rc6-mm2.orig/arch/frv/Kconfig	2006-09-15 12:17:39.847346146 -0500
+++ linux-2.6.18-rc6-mm2/arch/frv/Kconfig	2006-09-18 12:27:12.604083749 -0500
@@ -6,6 +6,10 @@ config FRV
 	bool
 	default y
 
+config ZONE_DMA
+	bool
+	default y
+
 config RWSEM_GENERIC_SPINLOCK
 	bool
 	default y
Index: linux-2.6.18-rc6-mm2/arch/m68knommu/Kconfig
===================================================================
--- linux-2.6.18-rc6-mm2.orig/arch/m68knommu/Kconfig	2006-09-15 12:17:39.860042528 -0500
+++ linux-2.6.18-rc6-mm2/arch/m68knommu/Kconfig	2006-09-18 12:27:12.630453081 -0500
@@ -17,6 +17,10 @@ config FPU
 	bool
 	default n
 
+config ZONE_DMA
+	bool
+	default y
+
 config RWSEM_GENERIC_SPINLOCK
 	bool
 	default y

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[PATCH 3/8] Optional ZONE_DMA in the VM

[Christoph Lameter]

Make ZONE_DMA optional in core code.

- ifdef all code for ZONE_DMA and related definitions following
  the example for ZONE_DMA32 and ZONE_HIGHMEM.

- Without ZONE_DMA, ZONE_HIGHMEM and ZONE_DMA32 we get to a
  ZONES_SHIFT of 0.

- Modify the VM statistics to work correctly without a DMA
  zone.

- Modify slab to not create DMA slabs if there is no
  ZONE_DMA.

Signed-off-by: Christoph Lameter <clameter@sgi.com>

Index: linux-2.6.18-rc6-mm2/include/linux/mmzone.h
===================================================================
--- linux-2.6.18-rc6-mm2.orig/include/linux/mmzone.h	2006-09-18 13:16:14.450122635 -0500
+++ linux-2.6.18-rc6-mm2/include/linux/mmzone.h	2006-09-18 13:16:29.139812806 -0500
@@ -91,6 +91,7 @@ struct per_cpu_pageset {
 #endif
 
 enum zone_type {
+#ifdef CONFIG_ZONE_DMA
 	/*
 	 * ZONE_DMA is used when there are devices that are not able
 	 * to do DMA to all of addressable memory (ZONE_NORMAL). Then we
@@ -111,6 +112,7 @@ enum zone_type {
 	 * 			<16M.
 	 */
 	ZONE_DMA,
+#endif
 #ifdef CONFIG_ZONE_DMA32
 	/*
 	 * x86_64 needs two ZONE_DMAs because it supports devices that are
@@ -148,7 +150,11 @@ enum zone_type {
  */
 
 #if !defined(CONFIG_ZONE_DMA32) && !defined(CONFIG_HIGHMEM)
+#if !defined(CONFIG_ZONE_DMA)
+#define ZONES_SHIFT 0
+#else
 #define ZONES_SHIFT 1
+#endif
 #else
 #define ZONES_SHIFT 2
 #endif
@@ -453,7 +459,11 @@ static inline int is_dma32(struct zone *
 
 static inline int is_dma(struct zone *zone)
 {
+#ifdef CONFIG_ZONE_DMA
 	return zone == zone->zone_pgdat->node_zones + ZONE_DMA;
+#else
+	return 0;
+#endif
 }
 
 /* These two functions are used to setup the per zone pages min values */
Index: linux-2.6.18-rc6-mm2/mm/page_alloc.c
===================================================================
--- linux-2.6.18-rc6-mm2.orig/mm/page_alloc.c	2006-09-18 13:16:18.945611213 -0500
+++ linux-2.6.18-rc6-mm2/mm/page_alloc.c	2006-09-18 13:16:29.159345669 -0500
@@ -71,7 +71,9 @@ static void __free_pages_ok(struct page 
  * don't need any ZONE_NORMAL reservation
  */
 int sysctl_lowmem_reserve_ratio[MAX_NR_ZONES-1] = {
+#ifdef CONFIG_ZONE_DMA
 	 256,
+#endif
 #ifdef CONFIG_ZONE_DMA32
 	 256,
 #endif
@@ -90,7 +92,9 @@ struct zone *zone_table[1 << ZONETABLE_S
 EXPORT_SYMBOL(zone_table);
 
 static char *zone_names[MAX_NR_ZONES] = {
+#ifdef CONFIG_ZONE_DMA
 	 "DMA",
+#endif
 #ifdef CONFIG_ZONE_DMA32
 	 "DMA32",
 #endif
Index: linux-2.6.18-rc6-mm2/include/linux/gfp.h
===================================================================
--- linux-2.6.18-rc6-mm2.orig/include/linux/gfp.h	2006-09-18 13:16:13.307450110 -0500
+++ linux-2.6.18-rc6-mm2/include/linux/gfp.h	2006-09-18 13:16:29.170088744 -0500
@@ -80,8 +80,10 @@ struct vm_area_struct;
 
 static inline enum zone_type gfp_zone(gfp_t flags)
 {
+#ifdef CONFIG_ZONE_DMA
 	if (flags & __GFP_DMA)
 		return ZONE_DMA;
+#endif
 #ifdef CONFIG_ZONE_DMA32
 	if (flags & __GFP_DMA32)
 		return ZONE_DMA32;
Index: linux-2.6.18-rc6-mm2/mm/slab.c
===================================================================
--- linux-2.6.18-rc6-mm2.orig/mm/slab.c	2006-09-18 13:16:15.423835889 -0500
+++ linux-2.6.18-rc6-mm2/mm/slab.c	2006-09-18 13:16:29.187668322 -0500
@@ -1441,13 +1441,14 @@ void __init kmem_cache_init(void)
 					ARCH_KMALLOC_FLAGS|SLAB_PANIC,
 					NULL, NULL);
 		}
-
+#ifdef CONFIG_ZONE_DMA
 		sizes->cs_dmacachep = kmem_cache_create(names->name_dma,
 					sizes->cs_size,
 					ARCH_KMALLOC_MINALIGN,
 					ARCH_KMALLOC_FLAGS|SLAB_CACHE_DMA|
 						SLAB_PANIC,
 					NULL, NULL);
+#endif
 		sizes++;
 		names++;
 	}
@@ -2275,8 +2276,10 @@ kmem_cache_create (const char *name, siz
 	cachep->slab_size = slab_size;
 	cachep->flags = flags;
 	cachep->gfpflags = 0;
+#ifdef CONFIG_ZONE_DMA
 	if (flags & SLAB_CACHE_DMA)
 		cachep->gfpflags |= GFP_DMA;
+#endif
 	cachep->buffer_size = size;
 
 	if (flags & CFLGS_OFF_SLAB) {
Index: linux-2.6.18-rc6-mm2/include/linux/slab.h
===================================================================
--- linux-2.6.18-rc6-mm2.orig/include/linux/slab.h	2006-09-18 13:07:52.648958109 -0500
+++ linux-2.6.18-rc6-mm2/include/linux/slab.h	2006-09-18 13:16:29.199388040 -0500
@@ -72,7 +72,11 @@ extern const char *kmem_cache_name(kmem_
 struct cache_sizes {
 	size_t		 cs_size;
 	kmem_cache_t	*cs_cachep;
+#ifdef CONFIG_ZONE_DMA
 	kmem_cache_t	*cs_dmacachep;
+#else
+#define cs_dmacachep cs_cachep
+#endif
 };
 extern struct cache_sizes malloc_sizes[];
 
Index: linux-2.6.18-rc6-mm2/mm/vmstat.c
===================================================================
--- linux-2.6.18-rc6-mm2.orig/mm/vmstat.c	2006-09-18 13:07:52.686070541 -0500
+++ linux-2.6.18-rc6-mm2/mm/vmstat.c	2006-09-18 13:16:29.207201186 -0500
@@ -437,6 +437,12 @@ struct seq_operations fragmentation_op =
 	.show	= frag_show,
 };
 
+#ifdef CONFIG_ZONE_DMA
+#define TEXT_FOR_DMA(xx) xx "_dma",
+#else
+#define TEXT_FOR_DMA(xx)
+#endif
+
 #ifdef CONFIG_ZONE_DMA32
 #define TEXT_FOR_DMA32(xx) xx "_dma32",
 #else
@@ -449,7 +455,7 @@ struct seq_operations fragmentation_op =
 #define TEXT_FOR_HIGHMEM(xx)
 #endif
 
-#define TEXTS_FOR_ZONES(xx) xx "_dma", TEXT_FOR_DMA32(xx) xx "_normal", \
+#define TEXTS_FOR_ZONES(xx) TEXT_FOR_DMA(xx) TEXT_FOR_DMA32(xx) xx "_normal", \
 					TEXT_FOR_HIGHMEM(xx)
 
 static char *vmstat_text[] = {
Index: linux-2.6.18-rc6-mm2/include/linux/vmstat.h
===================================================================
--- linux-2.6.18-rc6-mm2.orig/include/linux/vmstat.h	2006-09-18 13:07:52.660677824 -0500
+++ linux-2.6.18-rc6-mm2/include/linux/vmstat.h	2006-09-18 13:16:29.215990974 -0500
@@ -17,6 +17,12 @@
  * generated will simply be the increment of a global address.
  */
 
+#ifdef CONFIG_ZONE_DMA
+#define DMA_ZONE(xx) xx##_DMA,
+#else
+#define DMA_ZONE(xx)
+#endif
+
 #ifdef CONFIG_ZONE_DMA32
 #define DMA32_ZONE(xx) xx##_DMA32,
 #else
@@ -29,7 +35,7 @@
 #define HIGHMEM_ZONE(xx)
 #endif
 
-#define FOR_ALL_ZONES(xx) xx##_DMA, DMA32_ZONE(xx) xx##_NORMAL HIGHMEM_ZONE(xx)
+#define FOR_ALL_ZONES(xx) DMA_ZONE(xx) DMA32_ZONE(xx) xx##_NORMAL HIGHMEM_ZONE(xx)
 
 enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
 		FOR_ALL_ZONES(PGALLOC),
@@ -88,7 +94,8 @@ extern void vm_events_fold_cpu(int cpu);
 #endif /* CONFIG_VM_EVENT_COUNTERS */
 
 #define __count_zone_vm_events(item, zone, delta) \
-			__count_vm_events(item##_DMA + zone_idx(zone), delta)
+		__count_vm_events(item##_NORMAL - ZONE_NORMAL + \
+		zone_idx(zone), delta)
 
 /*
  * Zone based page accounting with per cpu differentials.
@@ -135,14 +142,16 @@ static inline unsigned long node_page_st
 	struct zone *zones = NODE_DATA(node)->node_zones;
 
 	return
+#ifdef CONFIG_ZONE_DMA
+		zone_page_state(&zones[ZONE_DMA], item) +
+#endif
 #ifdef CONFIG_ZONE_DMA32
 		zone_page_state(&zones[ZONE_DMA32], item) +
 #endif
-		zone_page_state(&zones[ZONE_NORMAL], item) +
 #ifdef CONFIG_HIGHMEM
 		zone_page_state(&zones[ZONE_HIGHMEM], item) +
 #endif
-		zone_page_state(&zones[ZONE_DMA], item);
+		zone_page_state(&zones[ZONE_NORMAL], item);
 }
 
 extern void zone_statistics(struct zonelist *, struct zone *);

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[PATCH 4/8] Optional ZONE_DMA for i386

[Christoph Lameter]

ZONE_DMA depends on GENERIC_ISA_DMA. We allow the user to configure
GENERIC_ISA_DMA. If it is switched off then ISA_DMA_API is also
switched off which will deselect all drivers that depend on ISA
functionality.

Signed-off-by: Christoph Lameter <clameter@sgi.com>

Index: linux-2.6.18-rc6-mm1/arch/i386/Kconfig
===================================================================
--- linux-2.6.18-rc6-mm1.orig/arch/i386/Kconfig	2006-09-08 06:42:11.697455315 -0500
+++ linux-2.6.18-rc6-mm1/arch/i386/Kconfig	2006-09-11 15:41:55.911259588 -0500
@@ -41,10 +41,6 @@
 config SBUS
 	bool
 
-config GENERIC_ISA_DMA
-	bool
-	default y
-
 config GENERIC_IOMAP
 	bool
 	default y
@@ -346,6 +342,15 @@
           XFree86 to initialize some video cards via BIOS. Disabling this
           option saves about 6k.
 
+config GENERIC_ISA_DMA
+	bool "ISA DMA zone (to support ISA legacy DMA)"
+	default y
+	help
+	  If DMA for ISA boards needs to be supported then this option
+	  needs to be enabled. An additional DMA zone for <16MB memory
+	  will be created and memory below 16MB will be used for those
+	  devices.
+
 config TOSHIBA
 	tristate "Toshiba Laptop support"
 	---help---
@@ -1071,6 +1076,7 @@
 
 config ISA_DMA_API
 	bool
+	depends on GENERIC_ISA_DMA
 	default y
 
 config ISA
Index: linux-2.6.18-rc6-mm1/arch/i386/kernel/Makefile
===================================================================
--- linux-2.6.18-rc6-mm1.orig/arch/i386/kernel/Makefile	2006-09-08 06:42:11.780470103 -0500
+++ linux-2.6.18-rc6-mm1/arch/i386/kernel/Makefile	2006-09-11 15:41:55.950325419 -0500
@@ -7,8 +7,9 @@
 obj-y	:= process.o signal.o entry.o traps.o irq.o \
 		ptrace.o time.o ioport.o ldt.o setup.o i8259.o sys_i386.o \
 		pci-dma.o i386_ksyms.o i387.o bootflag.o \
-		quirks.o i8237.o topology.o alternative.o i8253.o tsc.o
+		quirks.o topology.o alternative.o i8253.o tsc.o
 
+obj-$(CONFIG_GENERIC_ISA_DMA)	+= i8237.o
 obj-$(CONFIG_STACKTRACE)	+= stacktrace.o
 obj-y				+= cpu/
 obj-y				+= acpi/
Index: linux-2.6.18-rc6-mm1/arch/i386/kernel/setup.c
===================================================================
--- linux-2.6.18-rc6-mm1.orig/arch/i386/kernel/setup.c	2006-09-08 06:42:12.269769024 -0500
+++ linux-2.6.18-rc6-mm1/arch/i386/kernel/setup.c	2006-09-11 15:41:55.982554730 -0500
@@ -1075,13 +1075,17 @@
 {
 #ifdef CONFIG_HIGHMEM
 	unsigned long max_zone_pfns[MAX_NR_ZONES] = {
+#ifdef CONFIG_ZONE_DMA
 			virt_to_phys((char *)MAX_DMA_ADDRESS) >> PAGE_SHIFT,
+#endif
 			max_low_pfn,
 			highend_pfn};
 	add_active_range(0, 0, highend_pfn);
 #else
 	unsigned long max_zone_pfns[MAX_NR_ZONES] = {
+#ifdef CONFIG_ZONE_DMA
 			virt_to_phys((char *)MAX_DMA_ADDRESS) >> PAGE_SHIFT,
+#endif
 			max_low_pfn};
 	add_active_range(0, 0, max_low_pfn);
 #endif

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[PATCH 5/8] Optional ZONE_DMA for x86_64

[Christoph Lameter]

Allow the use to specify CONFIG_ZONE_DMA32 and CONFIG_ZONE_DMA (via
CONFIG_GENERIC_ISA_DMA). The default is on to be on the safe side.

If CONFIG_ZONE_DMA is off then devices requiring ISA DMA can no
longer be selected.

There are no drivers depending on CONFIG_ZONE_DMA32. If CONFIG_ZONE_DMA32
is not set then the system assumes that DMA devices are capable of
doing DMA to all of memory. This is frequently the case if

1. No memory exists over the 4GB boundary (careful, some motherboards
   equipped with 4GB memory will have memory show up above the 4GB
   boundary!). It is safe if one has 2GB or less memory in an
   x86_64 system.

2. The system has an IOMMU.

3. All devices using DMA are supporting DMA to all memory.

Signed-off-by: Christoph Lameter <clameter@sgi.com>

Index: linux-2.6.18-rc6-mm1/arch/x86_64/mm/init.c
===================================================================
--- linux-2.6.18-rc6-mm1.orig/arch/x86_64/mm/init.c	2006-09-11 16:06:41.705747849 -0500
+++ linux-2.6.18-rc6-mm1/arch/x86_64/mm/init.c	2006-09-11 16:08:13.190088058 -0500
@@ -406,9 +406,15 @@
 #ifndef CONFIG_NUMA
 void __init paging_init(void)
 {
-	unsigned long max_zone_pfns[MAX_NR_ZONES] = {MAX_DMA_PFN,
-							MAX_DMA32_PFN,
-							end_pfn};
+	unsigned long max_zone_pfns[MAX_NR_ZONES] = {
+#ifdef CONFIG_ZONE_DMA
+		MAX_DMA_PFN,
+#endif
+#ifdef CONFIG_ZONE_DMA32
+		MAX_DMA32_PFN,
+#endif
+		end_pfn
+	};
 	memory_present(0, 0, end_pfn);
 	sparse_init();
 	free_area_init_nodes(max_zone_pfns);
Index: linux-2.6.18-rc6-mm1/arch/x86_64/Kconfig
===================================================================
--- linux-2.6.18-rc6-mm1.orig/arch/x86_64/Kconfig	2006-09-11 16:06:41.713561013 -0500
+++ linux-2.6.18-rc6-mm1/arch/x86_64/Kconfig	2006-09-11 16:10:45.369039566 -0500
@@ -24,10 +24,6 @@
 	bool
 	default y
 
-config ZONE_DMA32
-	bool
-	default y
-
 config LOCKDEP_SUPPORT
 	bool
 	default y
@@ -73,10 +69,6 @@
 	bool
 	default y
 
-config GENERIC_ISA_DMA
-	bool
-	default y
-
 config GENERIC_IOMAP
 	bool
 	default y
@@ -251,6 +243,24 @@
 
 	  See <file:Documentation/mtrr.txt> for more information.
 
+config ZONE_DMA32
+	bool "32 Bit DMA Zone (only needed if memory >4GB)"
+	default y
+	help
+	  Some x64 configurations have 32 bit DMA controllers that cannot
+	  write to all of memory. If you have one of these and you have RAM
+	  beyond the 4GB boundary then enable this option.
+
+config GENERIC_ISA_DMA
+	bool "ISA DMA zone (to support ISA legacy DMA)"
+	default y
+	help
+	  If DMA for ISA boards needs to be supported then this option
+	  needs to be enabled. An additional DMA zone for <16MB memory
+	  will be created and memory below 16MB will be used for those
+	  devices. If this is deselected then devices that use ISA
+	  DMA will not be selectable.
+
 config SMP
 	bool "Symmetric multi-processing support"
 	---help---
@@ -611,6 +621,7 @@
 # we have no ISA slots, but we do have ISA-style DMA.
 config ISA_DMA_API
 	bool
+	depends on GENERIC_ISA_DMA
 	default y
 
 config GENERIC_PENDING_IRQ
Index: linux-2.6.18-rc6-mm1/arch/x86_64/kernel/Makefile
===================================================================
--- linux-2.6.18-rc6-mm1.orig/arch/x86_64/kernel/Makefile	2006-09-11 16:06:41.726257405 -0500
+++ linux-2.6.18-rc6-mm1/arch/x86_64/kernel/Makefile	2006-09-11 16:08:13.214504197 -0500
@@ -7,9 +7,10 @@
 obj-y	:= process.o signal.o entry.o traps.o irq.o \
 		ptrace.o time.o ioport.o ldt.o setup.o i8259.o sys_x86_64.o \
 		x8664_ksyms.o i387.o syscall.o vsyscall.o \
-		setup64.o bootflag.o e820.o reboot.o quirks.o i8237.o \
+		setup64.o bootflag.o e820.o reboot.o quirks.o \
 		pci-dma.o pci-nommu.o alternative.o early-quirks.o
 
+obj-$(CONFIG_GENERIC_ISA_DMA)	+= i8237.o
 obj-$(CONFIG_STACKTRACE)	+= stacktrace.o
 obj-$(CONFIG_X86_MCE)         += mce.o
 obj-$(CONFIG_X86_MCE_INTEL)	+= mce_intel.o

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[PATCH 6/8] Optional ZONE_DMA for ia64

[Christoph Lameter]

ZONE_DMA less operation for IA64 SGI platform

Disable ZONE_DMA for SGI SN2. All memory is addressable by all
devices and we do not need any special memory pool.

Signed-off-by: Christoph Lameter <clameter@sgi.com>

Index: linux-2.6.18-rc6-mm1/arch/ia64/mm/discontig.c
===================================================================
--- linux-2.6.18-rc6-mm1.orig/arch/ia64/mm/discontig.c	2006-09-11 16:42:07.206714114 -0500
+++ linux-2.6.18-rc6-mm1/arch/ia64/mm/discontig.c	2006-09-11 16:51:50.094129334 -0500
@@ -37,7 +37,9 @@
 	unsigned long pernode_size;
 	struct bootmem_data bootmem_data;
 	unsigned long num_physpages;
+#ifdef CONFIG_ZONE_DMA
 	unsigned long num_dma_physpages;
+#endif
 	unsigned long min_pfn;
 	unsigned long max_pfn;
 };
@@ -656,9 +658,11 @@
 
 	add_active_range(node, start >> PAGE_SHIFT, end >> PAGE_SHIFT);
 	mem_data[node].num_physpages += len >> PAGE_SHIFT;
+#ifdef CONFIG_ZONE_DMA
 	if (start <= __pa(MAX_DMA_ADDRESS))
 		mem_data[node].num_dma_physpages +=
 			(min(end, __pa(MAX_DMA_ADDRESS)) - start) >>PAGE_SHIFT;
+#endif
 	start = GRANULEROUNDDOWN(start);
 	start = ORDERROUNDDOWN(start);
 	end = GRANULEROUNDUP(end);
@@ -709,7 +713,9 @@
 			max_pfn = mem_data[node].max_pfn;
 	}
 
+#ifdef CONFIG_ZONE_DMA
 	max_zone_pfns[ZONE_DMA] = max_dma;
+#endif
 	max_zone_pfns[ZONE_NORMAL] = max_pfn;
 	free_area_init_nodes(max_zone_pfns);
 
Index: linux-2.6.18-rc6-mm1/arch/ia64/mm/contig.c
===================================================================
--- linux-2.6.18-rc6-mm1.orig/arch/ia64/mm/contig.c	2006-09-11 16:42:07.215503923 -0500
+++ linux-2.6.18-rc6-mm1/arch/ia64/mm/contig.c	2006-09-11 16:51:50.104872434 -0500
@@ -231,8 +231,10 @@
 	num_physpages = 0;
 	efi_memmap_walk(count_pages, &num_physpages);
 
+#ifdef CONFIG_ZONE_DMA
 	max_dma = virt_to_phys((void *) MAX_DMA_ADDRESS) >> PAGE_SHIFT;
 	max_zone_pfns[ZONE_DMA] = max_dma;
+#endif
 	max_zone_pfns[ZONE_NORMAL] = max_low_pfn;
 
 #ifdef CONFIG_VIRTUAL_MEM_MAP
Index: linux-2.6.18-rc6-mm1/arch/ia64/Kconfig
===================================================================
--- linux-2.6.18-rc6-mm1.orig/arch/ia64/Kconfig	2006-09-11 16:44:55.649739769 -0500
+++ linux-2.6.18-rc6-mm1/arch/ia64/Kconfig	2006-09-11 16:51:50.114638888 -0500
@@ -23,8 +23,8 @@
 	default y
 
 config ZONE_DMA
-	bool
-	default y
+	def_bool y
+	depends on !IA64_SGI_SN2
 
 config MMU
 	bool

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[PATCH 7/8] Remove ZONE_DMA remains from parisc

[Christoph Lameter]

Remove ZONE_DMA remains from parisc so that kernels are build without
ZONE_DMA.

Signed-off-by: Christoph Lameter <clameter@sgi.com>

Index: linux-2.6.18-rc6-mm2/arch/parisc/Kconfig
===================================================================
--- linux-2.6.18-rc6-mm2.orig/arch/parisc/Kconfig	2006-09-18 12:52:05.203892680 -0500
+++ linux-2.6.18-rc6-mm2/arch/parisc/Kconfig	2006-09-18 12:55:43.140754129 -0500
@@ -42,9 +42,6 @@ config TIME_LOW_RES
 	depends on SMP
 	default y
 
-config GENERIC_ISA_DMA
-	bool
-
 config GENERIC_HARDIRQS
 	def_bool y
 
Index: linux-2.6.18-rc6-mm2/arch/parisc/mm/init.c
===================================================================
--- linux-2.6.18-rc6-mm2.orig/arch/parisc/mm/init.c	2006-09-18 12:52:05.217565682 -0500
+++ linux-2.6.18-rc6-mm2/arch/parisc/mm/init.c	2006-09-18 12:55:43.153450483 -0500
@@ -808,9 +808,7 @@ void __init paging_init(void)
 	for (i = 0; i < npmem_ranges; i++) {
 		unsigned long zones_size[MAX_NR_ZONES] = { 0, };
 
-		/* We have an IOMMU, so all memory can go into a single
-		   ZONE_DMA zone. */
-		zones_size[ZONE_DMA] = pmem_ranges[i].pages;
+		zones_size[ZONE_NORMAL] = pmem_ranges[i].pages;
 
 #ifdef CONFIG_DISCONTIGMEM
 		/* Need to initialize the pfnnid_map before we can initialize

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[PATCH 8/8] Remove ZONE_DMA remains from sh/sh64

[Christoph Lameter]

sh / sh64: Remove ZONE_DMA remains.

Both arches do not need ZONE_DMA

Signed-off-by: Christoph Lameter <clameter@sgi.com>

Index: linux-2.6.18-rc6-mm2/arch/sh/mm/init.c
===================================================================
--- linux-2.6.18-rc6-mm2.orig/arch/sh/mm/init.c	2006-09-18 12:54:04.733274009 -0500
+++ linux-2.6.18-rc6-mm2/arch/sh/mm/init.c	2006-09-18 12:58:58.563038661 -0500
@@ -156,7 +156,6 @@ void __init paging_init(void)
 	 * Setup some defaults for the zone sizes.. these should be safe
 	 * regardless of distcontiguous memory or MMU settings.
 	 */
-	zones_size[ZONE_DMA] = 0 >> PAGE_SHIFT;
 	zones_size[ZONE_NORMAL] = __MEMORY_SIZE >> PAGE_SHIFT;
 #ifdef CONFIG_HIGHMEM
 	zones_size[ZONE_HIGHMEM] = 0 >> PAGE_SHIFT;
Index: linux-2.6.18-rc6-mm2/arch/sh64/mm/init.c
===================================================================
--- linux-2.6.18-rc6-mm2.orig/arch/sh64/mm/init.c	2006-09-18 12:54:04.745970361 -0500
+++ linux-2.6.18-rc6-mm2/arch/sh64/mm/init.c	2006-09-18 12:58:58.577688302 -0500
@@ -118,10 +118,7 @@ void __init paging_init(void)
 
 	mmu_context_cache = MMU_CONTEXT_FIRST_VERSION;
 
-        /*
-	 * All memory is good as ZONE_NORMAL (fall-through) and ZONE_DMA.
-         */
-	zones_size[ZONE_DMA] = MAX_LOW_PFN - START_PFN;
+	zones_size[ZONE_NORMAL] = MAX_LOW_PFN - START_PFN;
 	NODE_DATA(0)->node_mem_map = NULL;
 	free_area_init_node(0, NODE_DATA(0), zones_size, __MEMORY_START >> PAGE_SHIFT, 0);
 }
Index: linux-2.6.18-rc6-mm2/arch/sh64/Kconfig
===================================================================
--- linux-2.6.18-rc6-mm2.orig/arch/sh64/Kconfig	2006-09-18 12:33:04.000000000 -0500
+++ linux-2.6.18-rc6-mm2/arch/sh64/Kconfig	2006-09-18 13:01:07.919367272 -0500
@@ -36,9 +36,6 @@ config GENERIC_CALIBRATE_DELAY
 config RWSEM_XCHGADD_ALGORITHM
 	bool
 
-config GENERIC_ISA_DMA
-	bool
-
 source init/Kconfig
 
 menu "System type"

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Re: [PATCH 3/6] Optional ZONE_DMA in the VM

[Christoph Lameter]

On Tue, 12 Sep 2006, Nick Piggin wrote:

> I can't see from your patches, but what happens if someone asks
> for a GFP_DMA page or dma slab allocation when there is no ZONE_DMA?

The page/slab allocator will simply ignore the flag and return 
ZONE_NORMAL memory. See gfp_zone().

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Re: [PATCH 0/8] Optional ZONE_DMA V1

[Martin Bligh]

Resending. Your outbound email address is invalid
(Christoph Lameter <christoph@engr.sgi.com>), as is
the address for linux-mm


Christoph Lameter wrote:
> On Tue, 12 Sep 2006, Jack Steiner wrote:
> 
> 
>>I'm missing something here. On Altix, currently ALL of the memory is reported
>>as being in the DMA zone:
>>
>>	% cat /proc/budd*
>>	Node 0, zone      DMA   3015    116      4      1    ...
>>	Node 1, zone      DMA   4243    355     15      3    ...
>>	Node 2, zone      DMA   4384    113      6      4    ...
>>
>>	% cat /proc/zoneinfo
>>	Node 0, zone      DMA
>>	  pages free     5868
>>	  ...
>>
>>The DMA slabs are empty, though.
> 
> 
> This is wrong. All memory should be in ZONE_NORMAL since we have no DMA 
> restrictions on Altix.

PPC64 works the same way, I believe. All memory is DMA'able, therefore
it all fits in ZONE_DMA.

The real problem is that there's no consistent definition of what the
zones actually mean.

1. Is it DMA'able (this is stupid, as it doesn't say 'for what device'
2. Is it permanently mapped into kernel address space.

Given an inconsistent set of questions, it is unsuprising that we come
up with an inconsistent set of answers. We're trying to answer a 2D
question with a 1D answer.

What is really needed is to pass a physical address limit from the
caller, together with a flag that says whether the memory needs to be
mapped into the permanent kernel address space or not. The allocator
then finds the set of zones that will fulfill this criteria.
But I suspect this level of change will cause too many people to squeak
loudly.

M.

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Re: [PATCH 0/8] Optional ZONE_DMA V1

[Christoph Lameter]

On Tue, 12 Sep 2006, Martin Bligh wrote:

> > This is wrong. All memory should be in ZONE_NORMAL since we have no DMA
> > restrictions on Altix.
> 
> PPC64 works the same way, I believe. All memory is DMA'able, therefore
> it all fits in ZONE_DMA.

ZONE_DMA is for broken/limited DMA controllers not for DMA controllers 
that can reach all of memory.
 
> The real problem is that there's no consistent definition of what the
> zones actually mean.

ZONE_DMA 	Special memory area for DMA controllers that can only
			do dma to a restricted memory area.

ZONE_DMA32	Second special memory area for DMA controllers that
		can only do dma to a restricted memory area that
		is different from ZONE_DMA

ZONE_NORMAL	Regular memory

ZONE_HIGHEM	Memory requires being mapped into kernel address space.


> 1. Is it DMA'able (this is stupid, as it doesn't say 'for what device'

That is *not* what ZONE_DMA means. We have always supported DMA to 
regular  memory.

> What is really needed is to pass a physical address limit from the
> caller, together with a flag that says whether the memory needs to be
> mapped into the permanent kernel address space or not. The allocator
> then finds the set of zones that will fulfill this criteria.
> But I suspect this level of change will cause too many people to squeak
> loudly.

Actually we could do this with the proposed change of passing an 
allocation_control struct instead of gfpflags to the allocator functions. 
See the discussion on linux-mm.

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Re: [PATCH 0/8] Optional ZONE_DMA V1

[Christoph Lameter]

On Wed, 13 Sep 2006, Jes Sorensen wrote:

> > There was the floppy driver and one type of USB stick that I noticed 
> > during the work on the project. But other drivers may depend also depend 
> > indirectly on DMA functionality and may also be disabled.
> 
> Ok, USB should ring alarm bells, floppy I think is less relevant these
> days :)

If you want all drivers then you must of course have ZONE_DMA. 
Distributions that want to cover all drivers will have it on by default 
and ZONE_DMA is available by default.

However, if you want to create a lean and mean kernel then you can switch 
ZONE_DMA off and if there is just one zone left then the VM can 
optimized much better because loops are avoided and some macros 
become constant etc etc.

Some architectures never need ZONE_DMA because all hardware supports DMA 
to all of memory. SGI Altix is one example. Carrying an additional 
useless zone around unecessarily bloats the kernel both in term of code 
and data. Data is a particular issue since zones contain per cpu elements. 
For a 1k cpu 1k node configuration this saves around 1 million per cpu 
structures (one zone per node with 1k per cpu pagesets).

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Re: [PATCH 0/8] Optional ZONE_DMA V1

[Jack Steiner]

On Wed, Sep 13, 2006 at 10:23:10AM -0700, Christoph Lameter wrote:
> On Wed, 13 Sep 2006, Jes Sorensen wrote:
> 
> > > There was the floppy driver and one type of USB stick that I noticed 
> > > during the work on the project. But other drivers may depend also depend 
> > > indirectly on DMA functionality and may also be disabled.
> > 
> > Ok, USB should ring alarm bells, floppy I think is less relevant these
> > days :)
> 
> If you want all drivers then you must of course have ZONE_DMA. 
> Distributions that want to cover all drivers will have it on by default 
> and ZONE_DMA is available by default.
> 
> However, if you want to create a lean and mean kernel then you can switch 
> ZONE_DMA off and if there is just one zone left then the VM can 
> optimized much better because loops are avoided and some macros 
> become constant etc etc.
> 
> Some architectures never need ZONE_DMA because all hardware supports DMA 
> to all of memory. SGI Altix is one example. Carrying an additional 
> useless zone around unecessarily bloats the kernel both in term of code 
> and data. Data is a particular issue since zones contain per cpu elements. 
> For a 1k cpu 1k node configuration this saves around 1 million per cpu 
> structures (one zone per node with 1k per cpu pagesets).
> 

Most distros release GENERIC kernels for IA64. If _any_ IA64 platform requires 
ZONE_DMA, then it must be configured ON.

Two questions:

	- will any IA64 platform require that ZONE_DMA be enabled (I think
	  the answer is "yes")

	- if ZONE_DMA is enabled, ALTIX will still use only 1 zone. In your
	  statement above, you say that disabling ZONE_DMA save 1M cpu
	  structures. If ZONE_DMA is enabled, will these 1M structure be allocated
	  on SN even though they are not needed?

-- jack

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Re: [PATCH 0/8] Optional ZONE_DMA V1

[Christoph Lameter]

On Wed, 13 Sep 2006, Jack Steiner wrote:

> 	- will any IA64 platform require that ZONE_DMA be enabled (I think
> 	  the answer is "yes")

I think that still remains to be discussed. Today there are various means
to get around address restrictions.

> 	- if ZONE_DMA is enabled, ALTIX will still use only 1 zone. In your
> 	  statement above, you say that disabling ZONE_DMA save 1M cpu
> 	  structures. If ZONE_DMA is enabled, will these 1M structure be allocated
> 	  on SN even though they are not needed?

That has always been the case. In SLES9 and SLES10 we are using 1/4th of the pagesets.

Having no ZONE_DMA provides additional benefits besides saving memory. The 
VM balancing of allocations within a node becomes not necessary and 
various VM optimization can be performed. Loops are unrolled. Less zones 
have to be processed for draining / vm counter updates etc etc.


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Re: [PATCH 0/8] Optional ZONE_DMA V1

[Jes Sorensen]

Christoph Lameter wrote:
> On Wed, 13 Sep 2006, Jack Steiner wrote:
> 
>> 	- will any IA64 platform require that ZONE_DMA be enabled (I think
>> 	  the answer is "yes")
> 
> I think that still remains to be discussed. Today there are various means
> to get around address restrictions.

I don't know about USB on ia64, but USB is an issue and we do support
it even on Altix, as crazy as it may seem (I use USB with my SGI Prism
foot-warmer in the office). Also take into account that some ia64 boxes
do not come with IOMMU's, DIG - be afraid, be very afraid. On those
machines you ideally want to have DMA32 zone for this stuff to support
32 bit PCI devices, even if the swiotlb can be used (bounce buffers for
all transactions is just a sick idea), and we get back to the issue of
using generic kernels.

>> 	- if ZONE_DMA is enabled, ALTIX will still use only 1 zone. In your
>> 	  statement above, you say that disabling ZONE_DMA save 1M cpu
>> 	  structures. If ZONE_DMA is enabled, will these 1M structure be allocated
>> 	  on SN even though they are not needed?
> 
> That has always been the case. In SLES9 and SLES10 we are using 1/4th of the pagesets.
> 
> Having no ZONE_DMA provides additional benefits besides saving memory. The 
> VM balancing of allocations within a node becomes not necessary and 
> various VM optimization can be performed. Loops are unrolled. Less zones 
> have to be processed for draining / vm counter updates etc etc.

I agree it sounds appealing, but if reality is that all distro kernels
will switch ZONE_DMA on, then having the option to switch it off is
going have little or zero impact on the end users.

In other words, will this really matter in end user situations?

Cheers,
Jes

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Re: [PATCH 0/8] Optional ZONE_DMA V1

[Christoph Lameter]

On Thu, 14 Sep 2006, Jes Sorensen wrote:

> I don't know about USB on ia64, but USB is an issue and we do support
> it even on Altix, as crazy as it may seem (I use USB with my SGI Prism
> foot-warmer in the office). Also take into account that some ia64 boxes
> do not come with IOMMU's, DIG - be afraid, be very afraid. On those
> machines you ideally want to have DMA32 zone for this stuff to support
> 32 bit PCI devices, even if the swiotlb can be used (bounce buffers for
> all transactions is just a sick idea), and we get back to the issue of
> using generic kernels.

USB sticks that use ISA DMA is an issue but then IA64 does not 
support ISA DMA at all and would not even now support that USB stick type.

> I agree it sounds appealing, but if reality is that all distro kernels
> will switch ZONE_DMA on, then having the option to switch it off is
> going have little or zero impact on the end users.

I am sure that if we keep ZONE_DMA unconfigurable then the distros will 
never switch that off because they cannot. On the other hand if its 
optional then it can be switched off at some future date or special 
kernels can be build if this will turn out to be a big advantage.

Also not everyone (even we have the capability of generatic static SGI 
specific kernels) uses only distro kernels and this is a big memory saver 
and reduces complexity in the kernel with only a single zone.
 
> In other words, will this really matter in end user situations?

Certainly it will never have a change of mattering if we keep the 
chicken-and-egg argument going.

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Re: [PATCH 2/6] Introduce CONFIG_ZONE_DMA

[Christoph Lameter]

On Tue, 19 Sep 2006, Paul Mundt wrote:

> sh and sh64 have no use for ZONE_DMA, it's effectively ZONE_DMA ==
> ZONE_NORMAL anyways, so it can be safely switched off (though
> arch/sh/mm/init.c should then be changed to use ZONE_NORMAL if ZONE_DMA
> goes away, as we currently place all lowmem in ZONE_DMA, likewise for
> sh64). None of our DMA controllers have any particular limitations where
> ZONE_DMA would be useful at least.

Ok. I dropped the CONFIG_ZONE_DMA for sh so you will no longer have a DMA 
zone when this patch goes in.
 
sh64 has the same strange code as parisc:

config GENERIC_ISA_DMA
        bool

You do not have ISA_DMA so I should drop these lines?

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Re: [PATCH 2/6] Introduce CONFIG_ZONE_DMA

[Paul Mundt]

On Mon, Sep 18, 2006 at 10:33:00AM -0700, Christoph Lameter wrote:
> sh64 has the same strange code as parisc:
> 
> config GENERIC_ISA_DMA
>         bool
> 
> You do not have ISA_DMA so I should drop these lines?
> 
It doesn't really matter, this notation basically keeps it disabled
anyways (you'll note the absence of it from the defconfigs).

On Mon, Sep 18, 2006 at 11:36:55AM -0700, Christoph Lameter wrote:
> Index: linux-2.6.18-rc6-mm2/arch/sh/mm/init.c
> ===================================================================
> --- linux-2.6.18-rc6-mm2.orig/arch/sh/mm/init.c	2006-09-18 12:54:04.733274009 -0500
> +++ linux-2.6.18-rc6-mm2/arch/sh/mm/init.c	2006-09-18 12:58:58.563038661 -0500
> @@ -156,7 +156,6 @@ void __init paging_init(void)
>  	 * Setup some defaults for the zone sizes.. these should be safe
>  	 * regardless of distcontiguous memory or MMU settings.
>  	 */
> -	zones_size[ZONE_DMA] = 0 >> PAGE_SHIFT;
>  	zones_size[ZONE_NORMAL] = __MEMORY_SIZE >> PAGE_SHIFT;
>  #ifdef CONFIG_HIGHMEM
>  	zones_size[ZONE_HIGHMEM] = 0 >> PAGE_SHIFT;

You've missed the other ZONE_DMA references, if you scroll a bit further
down that's where we fill in ZONE_DMA, this is simply the default zone
layout that we rely on for nommu.

sh64 part looks fine.

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Re: [PATCH 2/6] Introduce CONFIG_ZONE_DMA

[Christoph Lameter]

On Tue, 19 Sep 2006, Paul Mundt wrote:

> You've missed the other ZONE_DMA references, if you scroll a bit further
> down that's where we fill in ZONE_DMA, this is simply the default zone
> layout that we rely on for nommu.

Are you sure that sh does not need ZONE_DMA? There is code in there
to check for the DMA boundary. The following patch disables that
code if CONFIG_ZONE_DMA is not set.



sh / sh64: Remove ZONE_DMA remains.

Both arches do not need ZONE_DMA

Signed-off-by: Christoph Lameter <clameter@sgi.com>

Index: linux-2.6.18-rc6-mm2/arch/sh/mm/init.c
===================================================================
--- linux-2.6.18-rc6-mm2.orig/arch/sh/mm/init.c	2006-09-18 13:27:48.125691412 -0500
+++ linux-2.6.18-rc6-mm2/arch/sh/mm/init.c	2006-09-18 17:56:23.632421140 -0500
@@ -156,7 +156,6 @@ void __init paging_init(void)
 	 * Setup some defaults for the zone sizes.. these should be safe
 	 * regardless of distcontiguous memory or MMU settings.
 	 */
-	zones_size[ZONE_DMA] = 0 >> PAGE_SHIFT;
 	zones_size[ZONE_NORMAL] = __MEMORY_SIZE >> PAGE_SHIFT;
 #ifdef CONFIG_HIGHMEM
 	zones_size[ZONE_HIGHMEM] = 0 >> PAGE_SHIFT;
@@ -186,13 +185,16 @@ void __init paging_init(void)
 		max_dma = virt_to_phys((char *)MAX_DMA_ADDRESS) >> PAGE_SHIFT;
 		low = MAX_LOW_PFN;
 
-		if (low < max_dma) {
-			zones_size[ZONE_DMA] = low - start_pfn;
-			zones_size[ZONE_NORMAL] = 0;
-		} else {
+#ifdef CONFIG_ZONE_DMA
+		if (low < max_dma)
+#endif
+			zones_size[ZONE_NORMAL] = low - start_pfn;
+#ifdef CONFIG_ZONE_DMA
+		else {
 			zones_size[ZONE_DMA] = max_dma - start_pfn;
 			zones_size[ZONE_NORMAL] = low - max_dma;
 		}
+#endif
 	}
 
 #elif defined(CONFIG_CPU_SH3) || defined(CONFIG_CPU_SH4)
Index: linux-2.6.18-rc6-mm2/arch/sh64/mm/init.c
===================================================================
--- linux-2.6.18-rc6-mm2.orig/arch/sh64/mm/init.c	2006-09-18 13:27:48.134481203 -0500
+++ linux-2.6.18-rc6-mm2/arch/sh64/mm/init.c	2006-09-18 17:54:14.263532486 -0500
@@ -118,10 +118,7 @@ void __init paging_init(void)
 
 	mmu_context_cache = MMU_CONTEXT_FIRST_VERSION;
 
-        /*
-	 * All memory is good as ZONE_NORMAL (fall-through) and ZONE_DMA.
-         */
-	zones_size[ZONE_DMA] = MAX_LOW_PFN - START_PFN;
+	zones_size[ZONE_NORMAL] = MAX_LOW_PFN - START_PFN;
 	NODE_DATA(0)->node_mem_map = NULL;
 	free_area_init_node(0, NODE_DATA(0), zones_size, __MEMORY_START >> PAGE_SHIFT, 0);
 }
Index: linux-2.6.18-rc6-mm2/arch/sh64/Kconfig
===================================================================
--- linux-2.6.18-rc6-mm2.orig/arch/sh64/Kconfig	2006-09-18 13:27:48.145224281 -0500
+++ linux-2.6.18-rc6-mm2/arch/sh64/Kconfig	2006-09-18 17:54:14.285995416 -0500
@@ -36,9 +36,6 @@ config GENERIC_CALIBRATE_DELAY
 config RWSEM_XCHGADD_ALGORITHM
 	bool
 
-config GENERIC_ISA_DMA
-	bool
-
 source init/Kconfig
 
 menu "System type"

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Re: [PATCH 2/6] Introduce CONFIG_ZONE_DMA

[Paul Mundt]

On Mon, Sep 18, 2006 at 03:58:52PM -0700, Christoph Lameter wrote:
> On Tue, 19 Sep 2006, Paul Mundt wrote:
> > You've missed the other ZONE_DMA references, if you scroll a bit further
> > down that's where we fill in ZONE_DMA, this is simply the default zone
> > layout that we rely on for nommu.
> 
> Are you sure that sh does not need ZONE_DMA? There is code in there
> to check for the DMA boundary. The following patch disables that
> code if CONFIG_ZONE_DMA is not set.
> 
Yes, MAX_DMA_ADDRESS (in include/asm-sh/dma.h) is from when we needed it for
alloc_bootmem(), we have no interest in it, but we can't kill off the
definition either since some drivers seem to rely on it.. It was also left
around in case some CPU variants with an arbitrary limitation in their
respective DMACs popped up.

All lowmem fits < MAX_DMA_ADDRESS and so gets stuffed in ZONE_DMA, as
per:

                if (low < max_dma) {
                        zones_size[ZONE_DMA] = low - start_pfn;
                        zones_size[ZONE_NORMAL] = 0;

So we may as well just do away with it entirely, via something like this:

Signed-off-by: Paul Mundt <lethal@linux-sh.org>

diff --git a/arch/sh/mm/init.c b/arch/sh/mm/init.c
index 8ea27ca..40494f9 100644
--- a/arch/sh/mm/init.c
+++ b/arch/sh/mm/init.c
@@ -156,7 +156,6 @@ void __init paging_init(void)
 	 * Setup some defaults for the zone sizes.. these should be safe
 	 * regardless of distcontiguous memory or MMU settings.
 	 */
-	zones_size[ZONE_DMA] = 0 >> PAGE_SHIFT;
 	zones_size[ZONE_NORMAL] = __MEMORY_SIZE >> PAGE_SHIFT;
 #ifdef CONFIG_HIGHMEM
 	zones_size[ZONE_HIGHMEM] = 0 >> PAGE_SHIFT;
@@ -168,7 +167,7 @@ #ifdef CONFIG_MMU
 	 * the zone sizes accordingly, in addition to turning it on.
 	 */
 	{
-		unsigned long max_dma, low, start_pfn;
+		unsigned long low, start_pfn;
 		pgd_t *pg_dir;
 		int i;
 
@@ -183,16 +182,10 @@ #ifdef CONFIG_MMU
 
 		/* Fixup the zone sizes */
 		start_pfn = START_PFN;
-		max_dma = virt_to_phys((char *)MAX_DMA_ADDRESS) >> PAGE_SHIFT;
 		low = MAX_LOW_PFN;
 
-		if (low < max_dma) {
-			zones_size[ZONE_DMA] = low - start_pfn;
-			zones_size[ZONE_NORMAL] = 0;
-		} else {
-			zones_size[ZONE_DMA] = max_dma - start_pfn;
-			zones_size[ZONE_NORMAL] = low - max_dma;
-		}
+		/* No DMA limitation, shove all of lowmem in ZONE_NORMAL. */
+		zones_size[ZONE_NORMAL] = low - start_pfn;
 	}
 
 #elif defined(CONFIG_CPU_SH3) || defined(CONFIG_CPU_SH4)

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[PATCH 0/8] Optional ZONE_DMA V1

[Christoph Lameter]

Optional ZONE_DMA

This patch follows up on the earlier work in Andrew's tree to reduce
the number of zones. The patches allow to go to a minimum of 2 zones.
This one allows also to make ZONE_DMA optional and therefore the
number of zones can be reduced to one.

ZONE_DMA is usually used for ISA DMA devices. Typically modern hardware
does not have any of these anymore. So we frequently do not need
the zone anymore. The presence of an additional zone unnecessarily
complicates VM operations. It must be scanned and balancing logic
must operate in it etc etc. If one has a 1-1 correspondence between
zones and nodes in a NUMA system then various other optimizations
become possible.

Many systems today (especially 64 bit but also 32 bit machines with less
than 4G of memory) can therefore operate just fine with a single zone.
With a single zone various loops can be optimized away by the
compiler. Many system currently do not place anything in ZONE_DMA. On
most of my systems ZONE_DMA is completely empty. Why constantly look
at an empty zone in /proc/zoneinfo and empty slab in /proc/slabinfo?
Non i386 also frequently have no need for ZONE_DMA and zones stay
empty.

The patchset was tested on i386 (UP / SMP), x86_64 (UP, NUMA) and
ia64 (NUMA).

The RFC posted earlier (see
http://marc.theaimsgroup.com/?l=linux-kernel&m=115231723513008&w=2)
had lots of #ifdefs in them. An effort has been made to minize the number
of #ifdefs and make this as compact as possible. The job was made much easier
by the ongoing efforts of others to extract common arch specific functionality.

I have been running this for awhile now on my desktop and finally Linux is
using all my available RAM instead of leaving the 16MB in ZONE_DMA untouched:

christoph@pentium940:~$ cat /proc/zoneinfo
Node 0, zone   Normal
  pages free     4435
        min      1448
        low      1810
        high     2172
        active   241786
        inactive 210170
        scanned  0 (a: 0 i: 0)
        spanned  524224
        present  524224
    nr_anon_pages 61680
    nr_mapped    14271
    nr_file_pages 390264
    nr_slab_reclaimable 27564
    nr_slab_unreclaimable 1793
    nr_page_table_pages 449
    nr_dirty     39
    nr_writeback 0
    nr_unstable  0
    nr_bounce    0
    cpu: 0 pcp: 0
              count: 156
              high:  186
              batch: 31
    cpu: 0 pcp: 1
              count: 9
              high:  62
              batch: 15
  vm stats threshold: 20
    cpu: 1 pcp: 0
              count: 177
              high:  186
              batch: 31
    cpu: 1 pcp: 1
              count: 12
              high:  62
              batch: 15
  vm stats threshold: 20
  all_unreclaimable: 0
  prev_priority:     12
  temp_priority:     12
  start_pfn:         0

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