mm/swapfile.c: delete the "last_in_cluster < scan_base" loop in the body of scan_swap_map()

Via commit ebc2a1a69111 ("swap: make cluster allocation per-cpu"), we
can find that all SWP_SOLIDSTATE "seek is cheap"(SSD case) has already
gone to si->cluster_info scan_swap_map_try_ssd_cluster() route.  So that
the "last_in_cluster < scan_base" loop in the body of scan_swap_map()
has already become a dead code snippet, and it should have been deleted.

This patch is to delete the redundant loop as Hugh and Shaohua
suggested.

[hughd@google.com: fix comment, simplify code]
Signed-off-by: Chen Yucong <slaoub@gmail.com>
Cc: Shaohua Li <shli@kernel.org>
Acked-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 3 insertions, 26 deletions

diff --git a/mm/swapfile.c b/mm/swapfile.c
index beeeef8a1b2d..4c524f7bd0bf 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -523,13 +523,10 @@ static unsigned long scan_swap_map(struct swap_info_struct *si,
                 /*
                  * If seek is expensive, start searching for new cluster from
                  * start of partition, to minimize the span of allocated swap.
-                 * But if seek is cheap, search from our current position, so
-                 * that swap is allocated from all over the partition: if the
-                 * Flash Translation Layer only remaps within limited zones,
-                 * we don't want to wear out the first zone too quickly.
+                 * If seek is cheap, that is the SWP_SOLIDSTATE si->cluster_info
+                 * case, just handled by scan_swap_map_try_ssd_cluster() above.
                  */
-                if (!(si->flags & SWP_SOLIDSTATE))
-                        scan_base = offset = si->lowest_bit;
+                scan_base = offset = si->lowest_bit;
                 last_in_cluster = offset + SWAPFILE_CLUSTER - 1;
 
                 /* Locate the first empty (unaligned) cluster */
@@ -549,26 +546,6 @@ static unsigned long scan_swap_map(struct swap_info_struct *si,
                         }
                 }
 
-                offset = si->lowest_bit;
-                last_in_cluster = offset + SWAPFILE_CLUSTER - 1;
-
-                /* Locate the first empty (unaligned) cluster */
-                for (; last_in_cluster < scan_base; offset++) {
-                        if (si->swap_map[offset])
-                                last_in_cluster = offset + SWAPFILE_CLUSTER;
-                        else if (offset == last_in_cluster) {
-                                spin_lock(&si->lock);
-                                offset -= SWAPFILE_CLUSTER - 1;
-                                si->cluster_next = offset;
-                                si->cluster_nr = SWAPFILE_CLUSTER - 1;
-                                goto checks;
-                        }
-                        if (unlikely(--latency_ration < 0)) {
-                                cond_resched();
-                                latency_ration = LATENCY_LIMIT;
-                        }
-                }
-
                 offset = scan_base;
                 spin_lock(&si->lock);
                 si->cluster_nr = SWAPFILE_CLUSTER - 1;