[RFC PATCH 06/10] mm, swap: hand the image's free clusters out in disk order

[Youngjun Park <youngjun.park@lge.com>]

The clusters set aside for the image come off the free list in the order
they were freed, so on a device that has been in use the image is
written back and forth across it.

Sort them by cluster index once they are set aside, so the image is
written front to back.  A rotating disk then writes it and reads it back
without seeking back and forth.

Assisted-by: Claude:claude-opus-5
Signed-off-by: Youngjun Park <youngjun.park@lge.com>
---
 mm/swap_hibernate.c | 9 +++++++++
 mm/swapfile.c       | 1 +
 2 files changed, 10 insertions(+)

diff --git a/mm/swap_hibernate.c b/mm/swap_hibernate.c
index 3431443716d4..23dc766f04cd 100644
--- a/mm/swap_hibernate.c
+++ b/mm/swap_hibernate.c
@@ -13,11 +13,20 @@ static struct swap_info_struct *hib_si;
 /* Free clusters set aside for the image, out of the allocator's reach. */
 static LIST_HEAD(hib_free_clusters);
 
+static int hib_cluster_cmp(void *priv, const struct list_head *a,
+			   const struct list_head *b)
+{
+	return list_entry(a, struct swap_cluster_info, list) <
+	       list_entry(b, struct swap_cluster_info, list) ? -1 : 1;
+}
+
 static void hib_claim_free_clusters(struct swap_info_struct *si)
 {
 	spin_lock(&si->lock);
 	list_splice_tail_init(&si->free_clusters, &hib_free_clusters);
 	spin_unlock(&si->lock);
+
+	list_sort(NULL, &hib_free_clusters, hib_cluster_cmp);
 }
 
 static void hib_return_free_clusters(struct swap_info_struct *si)
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 86ed8c6adae7..98ed75708661 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -38,6 +38,7 @@
 #include <linux/swapfile.h>
 #include <linux/export.h>
 #include <linux/sort.h>
+#include <linux/list_sort.h>
 #include <linux/completion.h>
 #include <linux/suspend.h>
 #include <linux/zswap.h>
-- 
2.48.1