[PATCH v2 06/15] mm, swap: rename and move some swap cluster definition and helpers

[Kairui Song <ryncsn@gmail.com>]

From: Kairui Song <kasong@tencent.com>

No feature change, move cluster related definitions and helpers to
mm/swap.h, also tidy up and add a "swap_" prefix for cluster lock/unlock
helpers, so they can be used outside of swap files. And while at it, add
kerneldoc.

Signed-off-by: Kairui Song <kasong@tencent.com>
Acked-by: Chris Li <chrisl@kernel.org>
Reviewed-by: Barry Song <baohua@kernel.org>
Acked-by: David Hildenbrand <david@redhat.com>
---
 include/linux/swap.h | 34 ----------------
 mm/swap.h            | 70 ++++++++++++++++++++++++++++++++
 mm/swapfile.c        | 97 +++++++++++++-------------------------------
 3 files changed, 99 insertions(+), 102 deletions(-)

diff --git a/include/linux/swap.h b/include/linux/swap.h
index 23452f014ca1..7e1fe4ff3d30 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -235,40 +235,6 @@ enum {
 /* Special value in each swap_map continuation */
 #define SWAP_CONT_MAX	0x7f	/* Max count */
 
-/*
- * We use this to track usage of a cluster. A cluster is a block of swap disk
- * space with SWAPFILE_CLUSTER pages long and naturally aligns in disk. All
- * free clusters are organized into a list. We fetch an entry from the list to
- * get a free cluster.
- *
- * The flags field determines if a cluster is free. This is
- * protected by cluster lock.
- */
-struct swap_cluster_info {
-	spinlock_t lock;	/*
-				 * Protect swap_cluster_info fields
-				 * other than list, and swap_info_struct->swap_map
-				 * elements corresponding to the swap cluster.
-				 */
-	u16 count;
-	u8 flags;
-	u8 order;
-	struct list_head list;
-};
-
-/* All on-list cluster must have a non-zero flag. */
-enum swap_cluster_flags {
-	CLUSTER_FLAG_NONE = 0, /* For temporary off-list cluster */
-	CLUSTER_FLAG_FREE,
-	CLUSTER_FLAG_NONFULL,
-	CLUSTER_FLAG_FRAG,
-	/* Clusters with flags above are allocatable */
-	CLUSTER_FLAG_USABLE = CLUSTER_FLAG_FRAG,
-	CLUSTER_FLAG_FULL,
-	CLUSTER_FLAG_DISCARD,
-	CLUSTER_FLAG_MAX,
-};
-
 /*
  * The first page in the swap file is the swap header, which is always marked
  * bad to prevent it from being allocated as an entry. This also prevents the
diff --git a/mm/swap.h b/mm/swap.h
index a69e18b12b45..39b27337bc0a 100644
--- a/mm/swap.h
+++ b/mm/swap.h
@@ -7,10 +7,80 @@ struct swap_iocb;
 
 extern int page_cluster;
 
+#ifdef CONFIG_THP_SWAP
+#define SWAPFILE_CLUSTER	HPAGE_PMD_NR
+#define swap_entry_order(order)	(order)
+#else
+#define SWAPFILE_CLUSTER	256
+#define swap_entry_order(order)	0
+#endif
+
+/*
+ * We use this to track usage of a cluster. A cluster is a block of swap disk
+ * space with SWAPFILE_CLUSTER pages long and naturally aligns in disk. All
+ * free clusters are organized into a list. We fetch an entry from the list to
+ * get a free cluster.
+ *
+ * The flags field determines if a cluster is free. This is
+ * protected by cluster lock.
+ */
+struct swap_cluster_info {
+	spinlock_t lock;	/*
+				 * Protect swap_cluster_info fields
+				 * other than list, and swap_info_struct->swap_map
+				 * elements corresponding to the swap cluster.
+				 */
+	u16 count;
+	u8 flags;
+	u8 order;
+	struct list_head list;
+};
+
+/* All on-list cluster must have a non-zero flag. */
+enum swap_cluster_flags {
+	CLUSTER_FLAG_NONE = 0, /* For temporary off-list cluster */
+	CLUSTER_FLAG_FREE,
+	CLUSTER_FLAG_NONFULL,
+	CLUSTER_FLAG_FRAG,
+	/* Clusters with flags above are allocatable */
+	CLUSTER_FLAG_USABLE = CLUSTER_FLAG_FRAG,
+	CLUSTER_FLAG_FULL,
+	CLUSTER_FLAG_DISCARD,
+	CLUSTER_FLAG_MAX,
+};
+
 #ifdef CONFIG_SWAP
 #include <linux/swapops.h> /* for swp_offset */
 #include <linux/blk_types.h> /* for bio_end_io_t */
 
+static inline struct swap_cluster_info *swp_offset_cluster(
+		struct swap_info_struct *si, pgoff_t offset)
+{
+	return &si->cluster_info[offset / SWAPFILE_CLUSTER];
+}
+
+/**
+ * swap_cluster_lock - Lock and return the swap cluster of given offset.
+ * @si: swap device the cluster belongs to.
+ * @offset: the swap entry offset, pointing to a valid slot.
+ *
+ * Context: The caller must ensure the offset is in the valid range and
+ * protect the swap device with reference count or locks.
+ */
+static inline struct swap_cluster_info *swap_cluster_lock(
+		struct swap_info_struct *si, unsigned long offset)
+{
+	struct swap_cluster_info *ci = swp_offset_cluster(si, offset);
+
+	spin_lock(&ci->lock);
+	return ci;
+}
+
+static inline void swap_cluster_unlock(struct swap_cluster_info *ci)
+{
+	spin_unlock(&ci->lock);
+}
+
 /* linux/mm/page_io.c */
 int sio_pool_init(void);
 struct swap_iocb;
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 1bd90f17440f..547ad4bfe1d8 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -58,9 +58,6 @@ static void swap_entries_free(struct swap_info_struct *si,
 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,
-					      unsigned long offset);
-static inline void unlock_cluster(struct swap_cluster_info *ci);
 
 static DEFINE_SPINLOCK(swap_lock);
 static unsigned int nr_swapfiles;
@@ -257,9 +254,9 @@ static int __try_to_reclaim_swap(struct swap_info_struct *si,
 	 * swap_map is HAS_CACHE only, which means the slots have no page table
 	 * reference or pending writeback, and can't be allocated to others.
 	 */
-	ci = lock_cluster(si, offset);
+	ci = swap_cluster_lock(si, offset);
 	need_reclaim = swap_only_has_cache(si, offset, nr_pages);
-	unlock_cluster(ci);
+	swap_cluster_unlock(ci);
 	if (!need_reclaim)
 		goto out_unlock;
 
@@ -384,19 +381,6 @@ static void discard_swap_cluster(struct swap_info_struct *si,
 	}
 }
 
-#ifdef CONFIG_THP_SWAP
-#define SWAPFILE_CLUSTER	HPAGE_PMD_NR
-
-#define swap_entry_order(order)	(order)
-#else
-#define SWAPFILE_CLUSTER	256
-
-/*
- * Define swap_entry_order() as constant to let compiler to optimize
- * out some code if !CONFIG_THP_SWAP
- */
-#define swap_entry_order(order)	0
-#endif
 #define LATENCY_LIMIT		256
 
 static inline bool cluster_is_empty(struct swap_cluster_info *info)
@@ -424,34 +408,12 @@ static inline unsigned int cluster_index(struct swap_info_struct *si,
 	return ci - si->cluster_info;
 }
 
-static inline struct swap_cluster_info *offset_to_cluster(struct swap_info_struct *si,
-							  unsigned long offset)
-{
-	return &si->cluster_info[offset / SWAPFILE_CLUSTER];
-}
-
 static inline unsigned int cluster_offset(struct swap_info_struct *si,
 					  struct swap_cluster_info *ci)
 {
 	return cluster_index(si, ci) * SWAPFILE_CLUSTER;
 }
 
-static inline struct swap_cluster_info *lock_cluster(struct swap_info_struct *si,
-						     unsigned long offset)
-{
-	struct swap_cluster_info *ci;
-
-	ci = offset_to_cluster(si, offset);
-	spin_lock(&ci->lock);
-
-	return ci;
-}
-
-static inline void unlock_cluster(struct swap_cluster_info *ci)
-{
-	spin_unlock(&ci->lock);
-}
-
 static void move_cluster(struct swap_info_struct *si,
 			 struct swap_cluster_info *ci, struct list_head *list,
 			 enum swap_cluster_flags new_flags)
@@ -807,7 +769,7 @@ static unsigned int alloc_swap_scan_cluster(struct swap_info_struct *si,
 	}
 out:
 	relocate_cluster(si, ci);
-	unlock_cluster(ci);
+	swap_cluster_unlock(ci);
 	if (si->flags & SWP_SOLIDSTATE) {
 		this_cpu_write(percpu_swap_cluster.offset[order], next);
 		this_cpu_write(percpu_swap_cluster.si[order], si);
@@ -874,7 +836,7 @@ static void swap_reclaim_full_clusters(struct swap_info_struct *si, bool force)
 		if (ci->flags == CLUSTER_FLAG_NONE)
 			relocate_cluster(si, ci);
 
-		unlock_cluster(ci);
+		swap_cluster_unlock(ci);
 		if (to_scan <= 0)
 			break;
 	}
@@ -913,7 +875,7 @@ static unsigned long cluster_alloc_swap_entry(struct swap_info_struct *si, int o
 		if (offset == SWAP_ENTRY_INVALID)
 			goto new_cluster;
 
-		ci = lock_cluster(si, offset);
+		ci = swap_cluster_lock(si, offset);
 		/* Cluster could have been used by another order */
 		if (cluster_is_usable(ci, order)) {
 			if (cluster_is_empty(ci))
@@ -921,7 +883,7 @@ static unsigned long cluster_alloc_swap_entry(struct swap_info_struct *si, int o
 			found = alloc_swap_scan_cluster(si, ci, offset,
 							order, usage);
 		} else {
-			unlock_cluster(ci);
+			swap_cluster_unlock(ci);
 		}
 		if (found)
 			goto done;
@@ -1202,7 +1164,7 @@ static bool swap_alloc_fast(swp_entry_t *entry,
 	if (!si || !offset || !get_swap_device_info(si))
 		return false;
 
-	ci = lock_cluster(si, offset);
+	ci = swap_cluster_lock(si, offset);
 	if (cluster_is_usable(ci, order)) {
 		if (cluster_is_empty(ci))
 			offset = cluster_offset(si, ci);
@@ -1210,7 +1172,7 @@ static bool swap_alloc_fast(swp_entry_t *entry,
 		if (found)
 			*entry = swp_entry(si->type, found);
 	} else {
-		unlock_cluster(ci);
+		swap_cluster_unlock(ci);
 	}
 
 	put_swap_device(si);
@@ -1478,14 +1440,14 @@ static void swap_entries_put_cache(struct swap_info_struct *si,
 	unsigned long offset = swp_offset(entry);
 	struct swap_cluster_info *ci;
 
-	ci = lock_cluster(si, offset);
-	if (swap_only_has_cache(si, offset, nr))
+	ci = swap_cluster_lock(si, offset);
+	if (swap_only_has_cache(si, offset, nr)) {
 		swap_entries_free(si, ci, entry, nr);
-	else {
+	} else {
 		for (int i = 0; i < nr; i++, entry.val++)
 			swap_entry_put_locked(si, ci, entry, SWAP_HAS_CACHE);
 	}
-	unlock_cluster(ci);
+	swap_cluster_unlock(ci);
 }
 
 static bool swap_entries_put_map(struct swap_info_struct *si,
@@ -1503,7 +1465,7 @@ static bool swap_entries_put_map(struct swap_info_struct *si,
 	if (count != 1 && count != SWAP_MAP_SHMEM)
 		goto fallback;
 
-	ci = lock_cluster(si, offset);
+	ci = swap_cluster_lock(si, offset);
 	if (!swap_is_last_map(si, offset, nr, &has_cache)) {
 		goto locked_fallback;
 	}
@@ -1512,21 +1474,20 @@ static bool swap_entries_put_map(struct swap_info_struct *si,
 	else
 		for (i = 0; i < nr; i++)
 			WRITE_ONCE(si->swap_map[offset + i], SWAP_HAS_CACHE);
-	unlock_cluster(ci);
+	swap_cluster_unlock(ci);
 
 	return has_cache;
 
 fallback:
-	ci = lock_cluster(si, offset);
+	ci = swap_cluster_lock(si, offset);
 locked_fallback:
 	for (i = 0; i < nr; i++, entry.val++) {
 		count = swap_entry_put_locked(si, ci, entry, 1);
 		if (count == SWAP_HAS_CACHE)
 			has_cache = true;
 	}
-	unlock_cluster(ci);
+	swap_cluster_unlock(ci);
 	return has_cache;
-
 }
 
 /*
@@ -1576,7 +1537,7 @@ static void swap_entries_free(struct swap_info_struct *si,
 	unsigned char *map_end = map + nr_pages;
 
 	/* It should never free entries across different clusters */
-	VM_BUG_ON(ci != offset_to_cluster(si, offset + nr_pages - 1));
+	VM_BUG_ON(ci != swp_offset_cluster(si, offset + nr_pages - 1));
 	VM_BUG_ON(cluster_is_empty(ci));
 	VM_BUG_ON(ci->count < nr_pages);
 
@@ -1651,9 +1612,9 @@ bool swap_entry_swapped(struct swap_info_struct *si, swp_entry_t entry)
 	struct swap_cluster_info *ci;
 	int count;
 
-	ci = lock_cluster(si, offset);
+	ci = swap_cluster_lock(si, offset);
 	count = swap_count(si->swap_map[offset]);
-	unlock_cluster(ci);
+	swap_cluster_unlock(ci);
 	return !!count;
 }
 
@@ -1676,7 +1637,7 @@ int swp_swapcount(swp_entry_t entry)
 
 	offset = swp_offset(entry);
 
-	ci = lock_cluster(si, offset);
+	ci = swap_cluster_lock(si, offset);
 
 	count = swap_count(si->swap_map[offset]);
 	if (!(count & COUNT_CONTINUED))
@@ -1699,7 +1660,7 @@ int swp_swapcount(swp_entry_t entry)
 		n *= (SWAP_CONT_MAX + 1);
 	} while (tmp_count & COUNT_CONTINUED);
 out:
-	unlock_cluster(ci);
+	swap_cluster_unlock(ci);
 	return count;
 }
 
@@ -1714,7 +1675,7 @@ static bool swap_page_trans_huge_swapped(struct swap_info_struct *si,
 	int i;
 	bool ret = false;
 
-	ci = lock_cluster(si, offset);
+	ci = swap_cluster_lock(si, offset);
 	if (nr_pages == 1) {
 		if (swap_count(map[roffset]))
 			ret = true;
@@ -1727,7 +1688,7 @@ static bool swap_page_trans_huge_swapped(struct swap_info_struct *si,
 		}
 	}
 unlock_out:
-	unlock_cluster(ci);
+	swap_cluster_unlock(ci);
 	return ret;
 }
 
@@ -2660,8 +2621,8 @@ static void wait_for_allocation(struct swap_info_struct *si)
 	BUG_ON(si->flags & SWP_WRITEOK);
 
 	for (offset = 0; offset < end; offset += SWAPFILE_CLUSTER) {
-		ci = lock_cluster(si, offset);
-		unlock_cluster(ci);
+		ci = swap_cluster_lock(si, offset);
+		swap_cluster_unlock(ci);
 	}
 }
 
@@ -3577,7 +3538,7 @@ static int __swap_duplicate(swp_entry_t entry, unsigned char usage, int nr)
 	offset = swp_offset(entry);
 	VM_WARN_ON(nr > SWAPFILE_CLUSTER - offset % SWAPFILE_CLUSTER);
 	VM_WARN_ON(usage == 1 && nr > 1);
-	ci = lock_cluster(si, offset);
+	ci = swap_cluster_lock(si, offset);
 
 	err = 0;
 	for (i = 0; i < nr; i++) {
@@ -3632,7 +3593,7 @@ static int __swap_duplicate(swp_entry_t entry, unsigned char usage, int nr)
 	}
 
 unlock_out:
-	unlock_cluster(ci);
+	swap_cluster_unlock(ci);
 	return err;
 }
 
@@ -3731,7 +3692,7 @@ int add_swap_count_continuation(swp_entry_t entry, gfp_t gfp_mask)
 
 	offset = swp_offset(entry);
 
-	ci = lock_cluster(si, offset);
+	ci = swap_cluster_lock(si, offset);
 
 	count = swap_count(si->swap_map[offset]);
 
@@ -3791,7 +3752,7 @@ int add_swap_count_continuation(swp_entry_t entry, gfp_t gfp_mask)
 out_unlock_cont:
 	spin_unlock(&si->cont_lock);
 out:
-	unlock_cluster(ci);
+	swap_cluster_unlock(ci);
 	put_swap_device(si);
 outer:
 	if (page)
-- 
2.51.0