rst: Collect stats about checked-vs-cowed pages

On restore we compare pages' contents with memcmp to check which
of them can remain shared. Report this info in restore stats.
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

cr-restore.c

@@ -397,6 +397,9 @@ static int restore_priv_vma_content(pid_t pid)
 		}
 	}
 
+	cnt_add(CNT_PAGES_COMPARED, nr_restored + nr_shared);
+	cnt_add(CNT_PAGES_SKIPPED_COW, nr_shared);
+
 	pr_info("nr_restored_pages: %d\n", nr_restored);
 	pr_info("nr_shared_pages:   %d\n", nr_shared);
 	pr_info("nr_droped_pages:   %d\n", nr_droped);

include/stats.h

@@ -23,7 +23,10 @@ enum {
 };
 
 enum {
-	RESTORE_CNT_NR_STATS = 1,
+	CNT_PAGES_COMPARED,
+	CNT_PAGES_SKIPPED_COW,
+
+	RESTORE_CNT_NR_STATS,
 };
 
 void cnt_add(int c, unsigned long val);

protobuf/stats.proto

@@ -11,6 +11,8 @@ message dump_stats_entry {
 }
 
 message restore_stats_entry {
+	required uint64	pages_compared = 1;
+	required uint64	pages_skipped_cow = 2;
 }
 
 message stats_entry {

stats.c

@@ -102,6 +102,9 @@ void write_stats(int what)
 	} else if (what == RESTORE_STATS) {
 		stats.restore = &rs_entry;
 
+		rs_entry.pages_compared = atomic_get(&rstats->counts[CNT_PAGES_COMPARED]);
+		rs_entry.pages_skipped_cow = atomic_get(&rstats->counts[CNT_PAGES_SKIPPED_COW]);
+
 		name = "restore";
 	} else
 		return;