stats: Add writing-memory-image timing

Dumping memory is draining it from parasite, for pre-dump
this time would be reasonably small. _Writing_ the memory
would occur _after_ tasks unseize and resume.
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

include/stats.h

@@ -6,6 +6,7 @@ enum {
 	TIME_FREEZING,
 	TIME_FROZEN,
 	TIME_MEMDUMP,
+	TIME_MEMWRITE,
 
 	TIME_NR_STATS,
 };

mem.c

@@ -358,6 +358,7 @@ static int __parasite_dump_pages_seized(struct parasite_ctl *ctl,
 		args->off += args->nr_segs;
 	}
 
+	timing_start(TIME_MEMWRITE);
 	ret = open_page_xfer(&xfer, CR_FD_PAGEMAP, ctl->pid.virt);
 	if (ret < 0)
 		goto out_pp;
@@ -365,6 +366,7 @@ static int __parasite_dump_pages_seized(struct parasite_ctl *ctl,
 	ret = page_xfer_dump_pages(&xfer, pp, 0);
 
 	xfer.close(&xfer);
+	timing_stop(TIME_MEMWRITE);
 	task_reset_dirty_track(ctl->pid.real);
 out_pp:
 	destroy_page_pipe(pp);

protobuf/stats.proto

@@ -3,6 +3,7 @@ message dump_stats_entry {
 	required uint32 freezing_time = 1;
 	required uint32 frozen_time = 2;
 	required uint32 memdump_time = 3;
+	required uint32	memwrite_time = 4;
 }
 
 message stats_entry {

stats.c

@@ -46,7 +46,7 @@ void timing_stop(int t)
 
 void show_stats(int fd)
 {
-	do_pb_show_plain(fd, PB_STATS, 1, NULL, "1.1:%u 1.2:%u 1.3:%u");
+	do_pb_show_plain(fd, PB_STATS, 1, NULL, "1.1:%u 1.2:%u 1.3:%u 1.4:%u");
 }
 
 static void encode_time(int t, u_int32_t *to)
@@ -68,6 +68,7 @@ void write_stats(int what)
 		encode_time(TIME_FREEZING, &dstats.freezing_time);
 		encode_time(TIME_FROZEN, &dstats.frozen_time);
 		encode_time(TIME_MEMDUMP, &dstats.memdump_time);
+		encode_time(TIME_MEMWRITE, &dstats.memwrite_time);
 
 		name = "dump";
 	} else