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/[email protected]
Signed-off-by: Kairui Song <[email protected]>
Reviewed-by: Baoquan He <[email protected]>
Cc: Barry Song <[email protected]>
Cc: Chis Li <[email protected]>
Cc: "Huang, Ying" <[email protected]>
Cc: Hugh Dickens <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Kalesh Singh <[email protected]>
Cc: Nhat Pham <[email protected]>
Cc: Ryan Roberts <[email protected]>
Cc: Yosry Ahmed <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: ryncsn

fs/btrfs/inode.c

@@ -10110,7 +10110,6 @@ static int btrfs_swap_activate(struct swap_info_struct *sis, struct file *file,
 	*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

fs/f2fs/data.c

@@ -4043,7 +4043,6 @@ static int check_swap_activate(struct swap_info_struct *sis,
 		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)",

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);

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 */

mm/page_io.c

@@ -163,7 +163,6 @@ int generic_swapfile_activate(struct swap_info_struct *sis,
 		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:

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 @@ int get_swap_pages(int n_goal, swp_entry_t swp_entries[], int entry_order)
 		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;