[PATCH 3/3] mm: adjust rss counters for migration entiries

[Konstantin Khlebnikov <khlebnikov@openvz.org>]

Memory migration fill pte with migration entry and it didn't update rss counters.
Then it replace migration entry with new page (or old one if migration was failed).
But between this two passes this pte can be unmaped, or task can fork child and
it will get copy of this migration entry. Nobody account this into rss counters.

This patch properly adjust rss counters for migration entries in zap_pte_range()
and copy_one_pte(). Thus we avoid extra atomic operations on migration fast-path.

Signed-off-by: Konstantin Khlebnikov <khlebnikov@openvz.org>
---
 mm/memory.c |   37 ++++++++++++++++++++++++++++---------
 1 files changed, 28 insertions(+), 9 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index 829d437..2f96ffc 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -878,15 +878,24 @@ copy_one_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm,
 			}
 			if (likely(!non_swap_entry(entry)))
 				rss[MM_SWAPENTS]++;
-			else if (is_write_migration_entry(entry) &&
-					is_cow_mapping(vm_flags)) {
-				/*
-				 * COW mappings require pages in both parent
-				 * and child to be set to read.
-				 */
-				make_migration_entry_read(&entry);
-				pte = swp_entry_to_pte(entry);
-				set_pte_at(src_mm, addr, src_pte, pte);
+			else if (is_migration_entry(entry)) {
+				page = migration_entry_to_page(entry);
+
+				if (PageAnon(page))
+					rss[MM_ANONPAGES]++;
+				else
+					rss[MM_FILEPAGES]++;
+
+				if (is_write_migration_entry(entry) &&
+				    is_cow_mapping(vm_flags)) {
+					/*
+					 * COW mappings require pages in both
+					 * parent and child to be set to read.
+					 */
+					make_migration_entry_read(&entry);
+					pte = swp_entry_to_pte(entry);
+					set_pte_at(src_mm, addr, src_pte, pte);
+				}
 			}
 		}
 		goto out_set_pte;
@@ -1191,6 +1200,16 @@ again:
 
 			if (!non_swap_entry(entry))
 				rss[MM_SWAPENTS]--;
+			else if (is_migration_entry(entry)) {
+				struct page *page;
+
+				page = migration_entry_to_page(entry);
+
+				if (PageAnon(page))
+					rss[MM_ANONPAGES]--;
+				else
+					rss[MM_FILEPAGES]--;
+			}
 			if (unlikely(!free_swap_and_cache(entry)))
 				print_bad_pte(vma, addr, ptent, NULL);
 		}