[RFC/RFT PATCH v2 0/1] arc: add sparsemem support

[RFC/RFT PATCH v2 0/1] arc: add sparsemem support

[Mike Rapoport]

From: Mike Rapoport <rppt@linux.ibm.com>

Hi,

It took me a while to get back to it, but better late than never :)

This patch adds SPARSEMEM support as an alternative to DISCONTIGMEM in
the case when there are two DRAM banks populated.

I've verified that it boots on nsim, but I could not find a way to make
nsim emulate two memory banks.

There is slight improvement in the resulting kernel size for
nsim_700_defconfig with CONFIG_HIGHMEM=y.

If sparse actually works on a system with 2 DRAM banks and does not
introduce performance regression, I suggest to update this patch to
replace DISCONTIGMEM with SPARSEMEM on arc.

$ size discontig/vmlinux  sparse/vmlinux 
   text	   data	    bss	    dec	    hex	filename
3894379	1093092	 244932	5232403	 4fd713	discontig/vmlinux
3879040	1093964	 244956	5217960	 4f9ea8	sparse/vmlinux

$ ./scripts/bloat-o-meter ~/tmp/arc/discontig/vmlinux  ~/tmp/arc/sparse/vmlinux 
add/remove: 35/23 grow/shrink: 35/384 up/down: 8110/-26438 (-18328)
...
Total: Before=4282217, After=4263889, chg -0.43%


Mike Rapoport (1):
  arc: add sparsemem support

 arch/arc/Kconfig                 | 10 ++++++++++
 arch/arc/include/asm/sparsemem.h | 13 +++++++++++++
 arch/arc/mm/init.c               |  7 ++++++-
 3 files changed, 29 insertions(+), 1 deletion(-)
 create mode 100644 arch/arc/include/asm/sparsemem.h

-- 
2.26.2


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[RFC/RFT PATCH v2 1/1] arc: add sparsemem support

[Mike Rapoport]

From: Mike Rapoport <rppt@linux.ibm.com>

Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
---
 arch/arc/Kconfig                 | 10 ++++++++++
 arch/arc/include/asm/sparsemem.h | 13 +++++++++++++
 arch/arc/mm/init.c               |  7 ++++++-
 3 files changed, 29 insertions(+), 1 deletion(-)
 create mode 100644 arch/arc/include/asm/sparsemem.h

diff --git a/arch/arc/Kconfig b/arch/arc/Kconfig
index 197896cfbd23..a3e4f9cc2fe7 100644
--- a/arch/arc/Kconfig
+++ b/arch/arc/Kconfig
@@ -49,6 +49,7 @@ config ARC
 	select PCI_SYSCALL if PCI
 	select PERF_USE_VMALLOC if ARC_CACHE_VIPT_ALIASING
 	select HAVE_ARCH_JUMP_LABEL if ISA_ARCV2 && !CPU_ENDIAN_BE32
+	select SPARSEMEM_STATIC if SPARSEMEM
 
 config ARCH_HAS_CACHE_LINE_SIZE
 	def_bool y
@@ -68,8 +69,15 @@ config GENERIC_CSUM
 config ARCH_DISCONTIGMEM_ENABLE
 	def_bool n
 
+config ARCH_SPARSEMEM_ENABLE
+	def_bool n
+
 config ARCH_FLATMEM_ENABLE
 	def_bool y
+	depends on !HIGHMEM
+
+config ARCH_SELECT_MEMORY_MODEL
+	def_bool n
 
 config MMU
 	def_bool y
@@ -509,6 +517,8 @@ config LINUX_RAM_BASE
 config HIGHMEM
 	bool "High Memory Support"
 	select ARCH_DISCONTIGMEM_ENABLE
+	select ARCH_SPARSEMEM_ENABLE
+	select ARCH_SELECT_MEMORY_MODEL
 	help
 	  With ARC 2G:2G address split, only upper 2G is directly addressable by
 	  kernel. Enable this to potentially allow access to rest of 2G and PAE
diff --git a/arch/arc/include/asm/sparsemem.h b/arch/arc/include/asm/sparsemem.h
new file mode 100644
index 000000000000..b23bedd9d6f0
--- /dev/null
+++ b/arch/arc/include/asm/sparsemem.h
@@ -0,0 +1,13 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_ARC_SPARSEMEM_H
+#define _ASM_ARC_SPARSEMEM_H
+
+#ifdef CONFIG_ARC_HAS_PAE40
+#define MAX_PHYSMEM_BITS	40
+#define SECTION_SIZE_BITS	32
+#else
+#define MAX_PHYSMEM_BITS	32
+#define SECTION_SIZE_BITS	31
+#endif
+
+#endif /* _ASM_ARC_SPARSEMEM_H */
diff --git a/arch/arc/mm/init.c b/arch/arc/mm/init.c
index e7bdc2ac1c87..eee8794aa172 100644
--- a/arch/arc/mm/init.c
+++ b/arch/arc/mm/init.c
@@ -153,7 +153,12 @@ void __init setup_arch_memory(void)
 	 * DISCONTIGMEM in turns requires multiple nodes. node 0 above is
 	 * populated with normal memory zone while node 1 only has highmem
 	 */
+#ifdef CONFIG_DISCONTIGMEM
 	node_set_online(1);
+#elif defined(CONFIG_SPARSEMEM)
+	memblocks_present();
+	sparse_init();
+#endif
 
 	min_high_pfn = PFN_DOWN(high_mem_start);
 	max_high_pfn = PFN_DOWN(high_mem_start + high_mem_sz);
@@ -162,7 +167,7 @@ void __init setup_arch_memory(void)
 
 	high_memory = (void *)(min_high_pfn << PAGE_SHIFT);
 	kmap_init();
-#endif
+#endif /* CONFIG_HIGHMEM */
 
 	free_area_init(max_zone_pfn);
 }
-- 
2.26.2


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