s390/mm: remove fake numa support

It turned out that fake numa support is rather useless on s390, since
there are no scenarios where there is any performance or other benefit
when used.

However it does provide maintenance cost and breaks from time to time.
Therefore remove it.

CONFIG_NUMA is still supported with a very small backend and only one
node. This way userspace applications which require NUMA interfaces
continue to work.

Note that NODES_SHIFT is set to 1 (= 2 nodes) instead of 0 (= 1 node),
since there is quite a bit of kernel code which assumes that more than
one node is possible if CONFIG_NUMA is enabled.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

arch/s390/Kconfig

@@ -450,14 +450,6 @@ config NR_CPUS
 config HOTPLUG_CPU
 	def_bool y
 
-# Some NUMA nodes have memory ranges that span
-# other nodes.	Even though a pfn is valid and
-# between a node's start and end pfns, it may not
-# reside on that node.	See memmap_init_zone()
-# for details. <- They meant memory holes!
-config NODES_SPAN_OTHER_NODES
-	def_bool NUMA
-
 config NUMA
 	bool "NUMA support"
 	depends on SCHED_TOPOLOGY
@@ -467,58 +459,9 @@ config NUMA
 
 	  This option adds NUMA support to the kernel.
 
-	  An operation mode can be selected by appending
-	  numa=<method> to the kernel command line.
-
-	  The default behaviour is identical to appending numa=plain to
-	  the command line. This will create just one node with all
-	  available memory and all CPUs in it.
-
 config NODES_SHIFT
-	int "Maximum NUMA nodes (as a power of 2)"
-	range 1 10
-	depends on NUMA
-	default "4"
-	help
-	  Specify the maximum number of NUMA nodes available on the target
-	  system. Increases memory reserved to accommodate various tables.
-
-menu "Select NUMA modes"
-	depends on NUMA
-
-config NUMA_EMU
-	bool "NUMA emulation"
-	default y
-	help
-	  Numa emulation mode will split the available system memory into
-	  equal chunks which then are distributed over the configured number
-	  of nodes in a round-robin manner.
-
-	  The number of fake nodes is limited by the number of available memory
-	  chunks (i.e. memory size / fake size) and the number of supported
-	  nodes in the kernel.
-
-	  The CPUs are assigned to the nodes in a way that partially respects
-	  the original machine topology (if supported by the machine).
-	  Fair distribution of the CPUs is not guaranteed.
-
-config EMU_SIZE
-	hex "NUMA emulation memory chunk size"
-	default 0x10000000
-	range 0x400000 0x100000000
-	depends on NUMA_EMU
-	help
-	  Select the default size by which the memory is chopped and then
-	  assigned to emulated NUMA nodes.
-
-	  This can be overridden by specifying
-
-	  emu_size=<n>
-
-	  on the kernel command line where also suffixes K, M, G, and T are
-	  supported.
-
-endmenu
+	int
+	default "1"
 
 config SCHED_SMT
 	def_bool n

arch/s390/include/asm/numa.h

@@ -13,24 +13,13 @@
 #ifdef CONFIG_NUMA
 
 #include <linux/numa.h>
-#include <linux/cpumask.h>
 
 void numa_setup(void);
-int numa_pfn_to_nid(unsigned long pfn);
-int __node_distance(int a, int b);
-void numa_update_cpu_topology(void);
-
-extern cpumask_t node_to_cpumask_map[MAX_NUMNODES];
-extern int numa_debug_enabled;
 
 #else
 
 static inline void numa_setup(void) { }
-static inline void numa_update_cpu_topology(void) { }
-static inline int numa_pfn_to_nid(unsigned long pfn)
-{
-	return 0;
-}
 
 #endif /* CONFIG_NUMA */
+
 #endif /* _ASM_S390_NUMA_H */

arch/s390/include/asm/topology.h

@@ -16,7 +16,6 @@ struct cpu_topology_s390 {
 	unsigned short socket_id;
 	unsigned short book_id;
 	unsigned short drawer_id;
-	unsigned short node_id;
 	unsigned short dedicated : 1;
 	cpumask_t thread_mask;
 	cpumask_t core_mask;
@@ -71,19 +70,23 @@ static inline void topology_expect_change(void) { }
 #define cpu_to_node cpu_to_node
 static inline int cpu_to_node(int cpu)
 {
-	return cpu_topology[cpu].node_id;
+	return 0;
 }
 
 /* Returns a pointer to the cpumask of CPUs on node 'node'. */
 #define cpumask_of_node cpumask_of_node
 static inline const struct cpumask *cpumask_of_node(int node)
 {
-	return &node_to_cpumask_map[node];
+	return cpu_possible_mask;
 }
 
 #define pcibus_to_node(bus) __pcibus_to_node(bus)
 
 #define node_distance(a, b) __node_distance(a, b)
+static inline int __node_distance(int a, int b)
+{
+	return 0;
+}
 
 #else /* !CONFIG_NUMA */
 

arch/s390/kernel/setup.c

@@ -790,6 +790,7 @@ static void __init memblock_add_mem_detect_info(void)
 		memblock_physmem_add(start, end - start);
 	}
 	memblock_set_bottom_up(false);
+	memblock_set_node(0, ULONG_MAX, &memblock.memory, 0);
 	memblock_dump_all();
 }
 

arch/s390/kernel/topology.c

@@ -26,7 +26,6 @@
 #include <linux/nodemask.h>
 #include <linux/node.h>
 #include <asm/sysinfo.h>
-#include <asm/numa.h>
 
 #define PTF_HORIZONTAL	(0UL)
 #define PTF_VERTICAL	(1UL)
@@ -267,7 +266,6 @@ static void update_cpu_masks(void)
 				cpumask_set_cpu(cpu, &cpus_with_topology);
 		}
 	}
-	numa_update_cpu_topology();
 }
 
 void store_topology(struct sysinfo_15_1_x *info)

arch/s390/numa/Makefile

@@ -1,4 +1,2 @@
 # SPDX-License-Identifier: GPL-2.0
 obj-y			+= numa.o
-obj-y			+= toptree.o
-obj-$(CONFIG_NUMA_EMU)	+= mode_emu.o