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

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>

diff --git a/mm/swapfile.c b/mm/swapfile.c
index beeeef8a1b2df2c5832432a6f8585b5010827d88..4c524f7bd0bfe69c23e2b28a13cad902ee3ac292 100644 (file)
--- 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;