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authorLinus Torvalds <torvalds@linux-foundation.org>2013-11-12 02:20:52 (GMT)
committerLinus Torvalds <torvalds@linux-foundation.org>2013-11-12 02:20:52 (GMT)
commit2612c49db3808f976ba12eed4170917f49693ac1 (patch)
tree7bb9fc021fe6acbc78ae87f54a001933b3cc5086 /arch/x86/mm
parent340286cd4e9aff841affb897f6d2535ed27605cf (diff)
parent6979287a7df66a92d6f308338e972a406f9ef842 (diff)
Merge branch 'x86-mm-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull x86 mm fixlet from Ingo Molnar: "One cleanup that documents a particular detail in init_mem_mapping()" * 'x86-mm-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: x86/mm: Add 'step_size' comments to init_mem_mapping()
Diffstat (limited to 'arch/x86/mm')
-rw-r--r--arch/x86/mm/init.c23
1 files changed, 20 insertions, 3 deletions
diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
index 04664cd..ce32017 100644
--- a/arch/x86/mm/init.c
+++ b/arch/x86/mm/init.c
@@ -399,8 +399,25 @@ static unsigned long __init init_range_memory_mapping(
return mapped_ram_size;
}
-/* (PUD_SHIFT-PMD_SHIFT)/2 */
-#define STEP_SIZE_SHIFT 5
+static unsigned long __init get_new_step_size(unsigned long step_size)
+{
+ /*
+ * Explain why we shift by 5 and why we don't have to worry about
+ * 'step_size << 5' overflowing:
+ *
+ * initial mapped size is PMD_SIZE (2M).
+ * We can not set step_size to be PUD_SIZE (1G) yet.
+ * In worse case, when we cross the 1G boundary, and
+ * PG_LEVEL_2M is not set, we will need 1+1+512 pages (2M + 8k)
+ * to map 1G range with PTE. Use 5 as shift for now.
+ *
+ * Don't need to worry about overflow, on 32bit, when step_size
+ * is 0, round_down() returns 0 for start, and that turns it
+ * into 0x100000000ULL.
+ */
+ return step_size << 5;
+}
+
void __init init_mem_mapping(void)
{
unsigned long end, real_end, start, last_start;
@@ -449,7 +466,7 @@ void __init init_mem_mapping(void)
min_pfn_mapped = last_start >> PAGE_SHIFT;
/* only increase step_size after big range get mapped */
if (new_mapped_ram_size > mapped_ram_size)
- step_size <<= STEP_SIZE_SHIFT;
+ step_size = get_new_step_size(step_size);
mapped_ram_size += new_mapped_ram_size;
}

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