How to boot up an ARM board enabled CONFIG_SPARSEMEM

[Zhang Zhen <zhenzhang.zhang@huawei.com>]

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Hi,

Recently We are testing stable kernel 3.10 on an ARM board.
It failed to boot if we enabled CONFIG_SPARSEMEM config.

Through the analysis, we found that mem_init() assumes the pages of different
sections are continuous.

But the truth is the pages of different sections are not continuous when
CONFIG_SPARSEMEM is enabled.

So now we have two ways to boot up when we enabled CONFIG_SPARSEMEM on an arm board.

1. In mem_init() and show_mem() compare pfn instead of page just like the patch in attachement.
2. Enable CONFIG_SPARSEMEM_ALLOC_MEM_MAP_TOGETHER when enabled CONFIG_SPARSEMEM.

QUESTION:

I want to know why CONFIG_SPARSEMEM_ALLOC_MEM_MAP_TOGETHER depends on x86_64 ?

Whether we can enable it on an ARM board ?

Or any other better solution ?


Best regards!




[-- Attachment #2: 0001-sparse-mem-compare-pfn-instead-of-page.patch --]
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>From c142b3157d4e0f9909076a24b6fe58c60afde0f3 Mon Sep 17 00:00:00 2001
From: Zhang Zhen <zhenzhang.zhang@huawei.com>
Date: Tue, 1 Jul 2014 14:59:19 +0800
Subject: [PATCH] sparse mem: compare pfn instead of page

If CONFIG_SPARSEMEM is enabled, here the pages of different
sections are not continuous.
So we compare pfn instead of page.

Signed-off-by: Zhang Zhen <zhenzhang.zhang@huawei.com>
---
 arch/arm/mm/init.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
index 0ecc43f..a36caac 100644
--- a/arch/arm/mm/init.c
+++ b/arch/arm/mm/init.c
@@ -115,6 +115,9 @@ void show_mem(unsigned int filter)
 
 		do {
 			total++;
+#if defined(CONFIG_SPARSEMEM) && defined(CONFIG_MACH_HI1380)
+			page = pfn_to_page(pfn1);
+#endif
 			if (PageReserved(page))
 				reserved++;
 			else if (PageSwapCache(page))
@@ -125,8 +128,13 @@ void show_mem(unsigned int filter)
 				free++;
 			else
 				shared += page_count(page) - 1;
+#if defined(CONFIG_SPARSEMEM) && defined(CONFIG_MACH_HI1380)
+			pfn1++;
+		} while (pfn1 < pfn2);
+#else
 			page++;
 		} while (page < end);
+#endif
 	}
 
 	printk("%d pages of RAM\n", total);
@@ -619,12 +627,21 @@ void __init mem_init(void)
 		end  = pfn_to_page(pfn2 - 1) + 1;
 
 		do {
+#if defined(CONFIG_SPARSEMEM) && defined(CONFIG_MACH_HI1380)
+			page = pfn_to_page(pfn1);
+#endif
 			if (PageReserved(page))
 				reserved_pages++;
 			else if (!page_count(page))
 				free_pages++;
+
+#if defined(CONFIG_SPARSEMEM) && defined(CONFIG_MACH_HI1380)
+			pfn1++;
+		} while (pfn1 < pfn2);
+#else
 			page++;
 		} while (page < end);
+#endif
 	}
 
 	/*
-- 
1.8.1.2