1 files changed, 34 insertions, 0 deletions

diff --git a/arch/x86_64/kernel/e820.c b/arch/x86_64/kernel/e820.c
index 6ded3a50dfe6..b548dea4e5b9 100644
--- a/arch/x86_64/kernel/e820.c
+++ b/arch/x86_64/kernel/e820.c
@@ -185,6 +185,40 @@ unsigned long __init e820_end_of_ram(void)
 }
 
 /* 
+ * Compute how much memory is missing in a range.
+ * Unlike the other functions in this file the arguments are in page numbers.
+ */
+unsigned long __init
+e820_hole_size(unsigned long start_pfn, unsigned long end_pfn)
+{
+        unsigned long ram = 0;
+        unsigned long start = start_pfn << PAGE_SHIFT;
+        unsigned long end = end_pfn << PAGE_SHIFT;
+        int i;
+        for (i = 0; i < e820.nr_map; i++) {
+                struct e820entry *ei = &e820.map[i];
+                unsigned long last, addr;
+
+                if (ei->type != E820_RAM ||
+                    ei->addr+ei->size <= start ||
+                    ei->addr >= end)
+                        continue;
+
+                addr = round_up(ei->addr, PAGE_SIZE);
+                if (addr < start)
+                        addr = start;
+
+                last = round_down(ei->addr + ei->size, PAGE_SIZE);
+                if (last >= end)
+                        last = end;
+
+                if (last > addr)
+                        ram += last - addr;
+        }
+        return ((end - start) - ram) >> PAGE_SHIFT;
+}
+
+/*
  * Mark e820 reserved areas as busy for the resource manager.
  */
 void __init e820_reserve_resources(void)