[Qemu-devel] [RFC kernel 1/2] mm: Add the functions used to get free pages information

[Liang Li]

get_total_pages_count() tries to get the page count of the system
RAM.
get_free_pages() is intend to construct a free pages bitmap by
traversing the free_list.

The free pages information will be sent to QEMU through virtio
and used for live migration optimization.

Signed-off-by: Liang Li <address@hidden>
---
 mm/page_alloc.c | 57 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 57 insertions(+)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 838ca8bb..81922e6 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3860,6 +3860,63 @@ void show_free_areas(unsigned int filter)
        show_swap_cache_info();
 }
 
+#define PFN_4G (0x100000000 >> PAGE_SHIFT)
+
+unsigned long get_total_pages_count(unsigned long low_mem)
+{
+       if (max_pfn >= PFN_4G) {
+               unsigned long pfn_gap = PFN_4G - (low_mem >> PAGE_SHIFT);
+
+               return max_pfn - pfn_gap;
+       } else
+               return max_pfn;
+}
+EXPORT_SYMBOL(get_total_pages_count);
+
+static void mark_free_pages_bitmap(struct zone *zone,
+                unsigned long *free_page_bitmap, unsigned long pfn_gap)
+{
+       unsigned long pfn, flags, i;
+       unsigned int order, t;
+       struct list_head *curr;
+
+       if (zone_is_empty(zone))
+               return;
+
+       spin_lock_irqsave(&zone->lock, flags);
+
+       for_each_migratetype_order(order, t) {
+               list_for_each(curr, &zone->free_area[order].free_list[t]) {
+
+                       pfn = page_to_pfn(list_entry(curr, struct page, lru));
+                       for (i = 0; i < (1UL << order); i++) {
+                               if ((pfn + i) >= PFN_4G)
+                                       set_bit_le(pfn + i - pfn_gap,
+                                                  free_page_bitmap);
+                               else
+                                       set_bit_le(pfn + i, free_page_bitmap);
+                       }
+               }
+       }
+
+       spin_unlock_irqrestore(&zone->lock, flags);
+}
+
+void get_free_pages(unsigned long *free_page_bitmap,
+               unsigned long *free_pages_count,
+               unsigned long low_mem)
+{
+       struct zone *zone;
+       unsigned long pfn_gap;
+
+       pfn_gap = PFN_4G - (low_mem >> PAGE_SHIFT);
+       for_each_populated_zone(zone)
+               mark_free_pages_bitmap(zone, free_page_bitmap, pfn_gap);
+
+       *free_pages_count = global_page_state(NR_FREE_PAGES);
+}
+EXPORT_SYMBOL(get_free_pages);
+
 static void zoneref_set_zone(struct zone *zone, struct zoneref *zoneref)
 {
        zoneref->zone = zone;
-- 
1.8.3.1