2014-06-02 11:55:51

by Chen Yucong

Subject: [PATCH] swap: Delete the "last_in_cluster < scan_base" loop in the body of scan_swap_map()

>From commit ebc2a1a69111, 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.

Signed-off-by: Chen Yucong <[email protected]>
---
mm/swapfile.c | 20 --------------------
1 file changed, 20 deletions(-)

diff --git a/mm/swapfile.c b/mm/swapfile.c
index beeeef8..1b44bd9 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -549,26 +549,6 @@ 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;
--
1.7.10.4

2014-06-02 23:27:48

by Hugh Dickins

Subject: Re: [PATCH] swap: Delete the "last_in_cluster < scan_base" loop in the body of scan_swap_map()

On Mon, 2 Jun 2014, Chen Yucong wrote:

> From commit ebc2a1a69111, 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.
>
> Signed-off-by: Chen Yucong <[email protected]>

That is very nice, thank you.

Acked-by: Hugh Dickins <[email protected]>

But it does beg for just a little more: perhaps Andrew can kindly fold in:
---

mm/swapfile.c | 9 +++------
1 file changed, 3 insertions(+), 6 deletions(-)

--- chen/mm/swapfile.c 2014-06-02 15:55:44.812368186 -0700
+++ hugh/mm/swapfile.c 2014-06-02 16:15:20.344396124 -0700
@@ -505,13 +505,10 @@ static unsigned long scan_swap_map(struc
/*
* 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 */