[PATCH] swap: Avoid scanning invalidated region for cheap seek

[Chen Yucong <slaoub@gmail.com>]

For cheap seek, when we scan the region between si->lowset_bit
and scan_base, if san_base is greater than si->highest_bit, the
scan operation between si->highest_bit and scan_base is not
unnecessary.

This patch can be used to avoid scanning invalidated region for
cheap seek.

Signed-off-by: Chen Yucong <slaoub@gmail.com>
---
 mm/swapfile.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/mm/swapfile.c b/mm/swapfile.c
index beeeef8..7f0f27e 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -489,6 +489,7 @@ static unsigned long scan_swap_map(struct swap_info_struct *si,
 {
 	unsigned long offset;
 	unsigned long scan_base;
+	unsigned long upper_bound;
 	unsigned long last_in_cluster = 0;
 	int latency_ration = LATENCY_LIMIT;
 
@@ -551,9 +552,11 @@ static unsigned long scan_swap_map(struct swap_info_struct *si,
 
 		offset = si->lowest_bit;
 		last_in_cluster = offset + SWAPFILE_CLUSTER - 1;
+		upper_bound = (scan_base <= si->highest_bit) ?
+				scan_base : (si->highest_bit + 1);
 
 		/* Locate the first empty (unaligned) cluster */
-		for (; last_in_cluster < scan_base; offset++) {
+		for (; last_in_cluster < upper_bound; offset++) {
 			if (si->swap_map[offset])
 				last_in_cluster = offset + SWAPFILE_CLUSTER;
 			else if (offset == last_in_cluster) {
-- 
1.7.10.4

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