mm, swap: clean up device availability check

Remove highest_bit and lowest_bit.  After the HDD allocation path has been
removed, the only purpose of these two fields is to determine whether the
device is full or not, which can instead be determined by checking the
inuse_pages.

Link: https://lkml.kernel.org/r/20250113175732.48099-6-ryncsn@gmail.com
Signed-off-by: Kairui Song <kasong@tencent.com>
Reviewed-by: Baoquan He <bhe@redhat.com>
Cc: Barry Song <v-songbaohua@oppo.com>
Cc: Chis Li <chrisl@kernel.org>
Cc: "Huang, Ying" <ying.huang@linux.alibaba.com>
Cc: Hugh Dickens <hughd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kalesh Singh <kaleshsingh@google.com>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Yosry Ahmed <yosryahmed@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

6 files changed, 8 insertions, 36 deletions

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 27b2fe7f735d..3b99b1e19371 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -10110,7 +10110,6 @@ out_unlock_mmap:
 	*span = bsi.highest_ppage - bsi.lowest_ppage + 1;
 	sis->max = bsi.nr_pages;
 	sis->pages = bsi.nr_pages - 1;
-	sis->highest_bit = bsi.nr_pages - 1;
 	return bsi.nr_extents;
 }
 #else
diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index a2478c2afb3a..a9eddd782dbc 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -4043,7 +4043,6 @@ retry:
 		cur_lblock = 1;	/* force Empty message */
 	sis->max = cur_lblock;
 	sis->pages = cur_lblock - 1;
-	sis->highest_bit = cur_lblock - 1;
 out:
 	if (not_aligned)
 		f2fs_warn(sbi, "Swapfile (%u) is not align to section: 1) creat(), 2) ioctl(F2FS_IOC_SET_PIN_FILE), 3) fallocate(%lu * N)",
diff --git a/fs/iomap/swapfile.c b/fs/iomap/swapfile.c
index 5fc0ac36dee3..b90d0eda9e51 100644
--- a/fs/iomap/swapfile.c
+++ b/fs/iomap/swapfile.c
@@ -189,7 +189,6 @@ int iomap_swapfile_activate(struct swap_info_struct *sis,
 	*pagespan = 1 + isi.highest_ppage - isi.lowest_ppage;
 	sis->max = isi.nr_pages;
 	sis->pages = isi.nr_pages - 1;
-	sis->highest_bit = isi.nr_pages - 1;
 	return isi.nr_extents;
 }
 EXPORT_SYMBOL_GPL(iomap_swapfile_activate);
diff --git a/include/linux/swap.h b/include/linux/swap.h
index 3a71198a6957..c0d49dad7a4b 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -305,8 +305,6 @@ struct swap_info_struct {
 	struct list_head frag_clusters[SWAP_NR_ORDERS];
 					/* list of cluster that are fragmented or contented */
 	unsigned int frag_cluster_nr[SWAP_NR_ORDERS];
-	unsigned int lowest_bit;	/* index of first free in swap_map */
-	unsigned int highest_bit;	/* index of last free in swap_map */
 	unsigned int pages;		/* total of usable pages of swap */
 	unsigned int inuse_pages;	/* number of those currently in use */
 	struct percpu_cluster __percpu *percpu_cluster; /* per cpu's swap location */
diff --git a/mm/page_io.c b/mm/page_io.c
index 4b4ea8e49cf6..9b983de351f9 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -163,7 +163,6 @@ reprobe:
 		page_no = 1;	/* force Empty message */
 	sis->max = page_no;
 	sis->pages = page_no - 1;
-	sis->highest_bit = page_no - 1;
 out:
 	return ret;
 bad_bmap:
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 83ebc24cc94b..2686032d3510 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -55,7 +55,7 @@ static bool swap_count_continued(struct swap_info_struct *, pgoff_t,
 static void free_swap_count_continuations(struct swap_info_struct *);
 static void swap_entry_range_free(struct swap_info_struct *si, swp_entry_t entry,
 				  unsigned int nr_pages);
-static void swap_range_alloc(struct swap_info_struct *si, unsigned long offset,
+static void swap_range_alloc(struct swap_info_struct *si,
 			     unsigned int nr_entries);
 static bool folio_swapcache_freeable(struct folio *folio);
 static struct swap_cluster_info *lock_cluster(struct swap_info_struct *si,
@@ -650,7 +650,7 @@ static bool cluster_alloc_range(struct swap_info_struct *si, struct swap_cluster
 	}
 
 	memset(si->swap_map + start, usage, nr_pages);
-	swap_range_alloc(si, start, nr_pages);
+	swap_range_alloc(si, nr_pages);
 	ci->count += nr_pages;
 
 	if (ci->count == SWAPFILE_CLUSTER) {
@@ -888,19 +888,11 @@ static void del_from_avail_list(struct swap_info_struct *si)
 	spin_unlock(&swap_avail_lock);
 }
 
-static void swap_range_alloc(struct swap_info_struct *si, unsigned long offset,
+static void swap_range_alloc(struct swap_info_struct *si,
 			     unsigned int nr_entries)
 {
-	unsigned int end = offset + nr_entries - 1;
-
-	if (offset == si->lowest_bit)
-		si->lowest_bit += nr_entries;
-	if (end == si->highest_bit)
-		WRITE_ONCE(si->highest_bit, si->highest_bit - nr_entries);
 	WRITE_ONCE(si->inuse_pages, si->inuse_pages + nr_entries);
 	if (si->inuse_pages == si->pages) {
-		si->lowest_bit = si->max;
-		si->highest_bit = 0;
 		del_from_avail_list(si);
 
 		if (vm_swap_full())
@@ -933,15 +925,8 @@ static void swap_range_free(struct swap_info_struct *si, unsigned long offset,
 	for (i = 0; i < nr_entries; i++)
 		clear_bit(offset + i, si->zeromap);
 
-	if (offset < si->lowest_bit)
-		si->lowest_bit = offset;
-	if (end > si->highest_bit) {
-		bool was_full = !si->highest_bit;
-
-		WRITE_ONCE(si->highest_bit, end);
-		if (was_full && (si->flags & SWP_WRITEOK))
-			add_to_avail_list(si);
-	}
+	if (si->inuse_pages == si->pages)
+		add_to_avail_list(si);
 	if (si->flags & SWP_BLKDEV)
 		swap_slot_free_notify =
 			si->bdev->bd_disk->fops->swap_slot_free_notify;
@@ -1051,15 +1036,12 @@ start_over:
 		plist_requeue(&si->avail_lists[node], &swap_avail_heads[node]);
 		spin_unlock(&swap_avail_lock);
 		spin_lock(&si->lock);
-		if (!si->highest_bit || !(si->flags & SWP_WRITEOK)) {
+		if ((si->inuse_pages == si->pages) || !(si->flags & SWP_WRITEOK)) {
 			spin_lock(&swap_avail_lock);
 			if (plist_node_empty(&si->avail_lists[node])) {
 				spin_unlock(&si->lock);
 				goto nextsi;
 			}
-			WARN(!si->highest_bit,
-			     "swap_info %d in list but !highest_bit\n",
-			     si->type);
 			WARN(!(si->flags & SWP_WRITEOK),
 			     "swap_info %d in list but !SWP_WRITEOK\n",
 			     si->type);
@@ -2441,8 +2423,8 @@ static void _enable_swap_info(struct swap_info_struct *si)
 	 */
 	plist_add(&si->list, &swap_active_head);
 
-	/* add to available list iff swap device is not full */
-	if (si->highest_bit)
+	/* add to available list if swap device is not full */
+	if (si->inuse_pages < si->pages)
 		add_to_avail_list(si);
 }
 
@@ -2606,7 +2588,6 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
 	drain_mmlist();
 
 	/* wait for anyone still in scan_swap_map_slots */
-	p->highest_bit = 0;		/* cuts scans short */
 	while (p->flags >= SWP_SCANNING) {
 		spin_unlock(&p->lock);
 		spin_unlock(&swap_lock);
@@ -2941,8 +2922,6 @@ static unsigned long read_swap_header(struct swap_info_struct *si,
 		return 0;
 	}
 
-	si->lowest_bit  = 1;
-
 	maxpages = swapfile_maximum_size;
 	last_page = swap_header->info.last_page;
 	if (!last_page) {
@@ -2959,7 +2938,6 @@ static unsigned long read_swap_header(struct swap_info_struct *si,
 		if ((unsigned int)maxpages == 0)
 			maxpages = UINT_MAX;
 	}
-	si->highest_bit = maxpages - 1;
 
 	if (!maxpages)
 		return 0;