I was bisecting a problem on 64bit where any attempt to cause a crash kernel to boot would hang. The bisect ended up on commit 722bc6b (x86/mm: Fix the size calculation of mapping tables) and somehow, looking at the calling function and the ranges printed on boot, I think the calculations should only be done in the 32bit case. On 64bit: [ 0.000000] init_memory_mapping: [mem 0x00000000-0x77e87fff] [ 0.000000] [mem 0x00000000-0x77dfffff] page 2M [ 0.000000] [mem 0x77e00000-0x77e87fff] page 4k Attached patch would fix this if you agree with it. Thanks. -Stefan From 6b679d1af20656929c0e829f29eed60b0a86a74f Mon Sep 17 00:00:00 2001 From: Stefan Bader Date: Fri, 13 Jul 2012 15:16:33 +0200 Subject: [PATCH] x86/mm: Limit 2/4M size calculation to x86_32 commit 722bc6b (x86/mm: Fix the size calculation of mapping tables) did modify the extra space calculation for mapping tables in order to make up for the first 2/4M memory range using 4K pages. However this setup is only used when compiling for 32bit. On 64bit there is only the trailing area of 4K pages (which is already added). The code was already adapted once for things went wrong on a 8TB machine (bd2753b x86/mm: Only add extra pages count for the first memory range during pre-allocation early page table space), but it looks a bit like it currently would overdo things for 64bit. I only noticed while bisecting for the reason I could not make a crash kernel boot (which ended up on this patch). Signed-off-by: Stefan Bader Cc: WANG Cong Cc: Yinghai Lu Cc: Tejun Heo --- diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c index bc4e9d8..636bbfd 100644 --- a/arch/x86/mm/init.c +++ b/arch/x86/mm/init.c @@ -60,10 +60,11 @@ static void __init find_early_table_space(struct map_range *mr, unsigned long en extra = end - ((end>>PMD_SHIFT) << PMD_SHIFT); #ifdef CONFIG_X86_32 extra += PMD_SIZE; -#endif + /* The first 2/4M doesn't use large pages. */ if (mr->start < PMD_SIZE) extra += mr->end - mr->start; +#endif ptes = (extra + PAGE_SIZE - 1) >> PAGE_SHIFT; } else -- 1.7.9.5