[RFC] MADV_FREE doesn't work when doesn't have swap partition

[Wang, Yalin]

I notice this commit:
mm: support madvise(MADV_FREE),

it can free clean anonymous pages directly,
doesn't need pageout to swap partition,

but I found it doesn't work on my platform,
which don't enable any swap partitions.

I make a change for this.
Just to explain my issue clearly,
Do we need some other checks to still scan anonymous pages even
Don't have swap partition but have clean anonymous pages?
---
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 5e8772b..8258f3a 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1941,7 +1941,7 @@ static void get_scan_count(struct lruvec *lruvec, int swappiness,
                force_scan = true;

        /* If we have no swap space, do not bother scanning anon pages. */
-       if (!sc->may_swap || (get_nr_swap_pages() <= 0)) {
+       if (!sc->may_swap) {
                scan_balance = SCAN_FILE;
                goto out;
        }