[PATCH] swapinfo accounting

Randy observed that 2.5 /proc/meminfo SwapFree holds steady
while SwapTotal goes up and down: wrong way round!

Andrew pointed to wrong conditional in si_swapinfo(): 2.5.4
updated it incorrectly when new flags bit was briefly added.
And pointed out that it also makes si_swapinfo much too slow.

mm/swapfile.c

@@ -1095,7 +1095,8 @@ void si_swapinfo(struct sysinfo *val)
 	swap_list_lock();
 	for (i = 0; i < nr_swapfiles; i++) {
 		unsigned int j;
-		if (!(swap_info[i].flags & SWP_USED))
+		if (!(swap_info[i].flags & SWP_USED) ||
+		     (swap_info[i].flags & SWP_WRITEOK))
 			continue;
 		for (j = 0; j < swap_info[i].max; ++j) {
 			switch (swap_info[i].swap_map[j]) {