[PATCH] realtime swapspace accounting

There are a couple of statistical functions which scan the entire swap
map counting things up, to display in /proc.

On my machine, these hold spinlocks for 19 milliseconds which is
unacceptable from a scheduling latency point of view.

And an application which sits in a loop reading /proc/swaps on a large
machine is probably a decent denial-of-service attack - it will limit
swap allocations to tens of pages per second.

So add a counter to swap_info_struct and use it to track how many pages
are currently in use, so those reporting functions don't need to add
them all up.

1 files changed, 1 insertions, 0 deletions

diff --git a/include/linux/swap.h b/include/linux/swap.h
index 8ad50c284b45..d74f0800ab32 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -121,6 +121,7 @@ struct swap_info_struct {
 	int prio;			/* swap priority */
 	int pages;
 	unsigned long max;
+	unsigned long inuse_pages;
 	int next;			/* next entry on swap list */
 };