As request by hpa, add comments for why we choose 5 for
step size shift.
Signed-off-by: Yinghai Lu <ying...@kernel.org>
---
arch/x86/mm/init.c | 21 ++++++++++++++++++---
1 file changed, 18 insertions(+), 3 deletions(-)
diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
index 28b294f..2754e45 100644
--- a/arch/x86/mm/init.c
+++ b/arch/x86/mm/init.c
@@ -385,8 +385,23 @@ 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)
+{
+ /*
+ * initial mapped size is PMD_SIZE, aka 2M.
+ * We can not set step_size to be PUD_SIZE aka 1G yet.
+ * In worse case, when 1G is cross the 1G boundary, and
+ * PG_LEVEL_2M is not set, we will need 1+1+512 pages (aka 2M + 8k)
+ * to map 1G range with PTE. Use 5 as shift for now.
+ */
+ unsigned long new_step_size = step_size << 5;
+
+ if (new_step_size > step_size)
+ step_size = new_step_size;
+
+ return step_size;
+}
+
void __init init_mem_mapping(void)
{
unsigned long end, real_end, start, last_start;
@@ -428,7 +443,7 @@ 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;
}
--
1.8.1.4
--
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