Message-ID: <20250429233848.3093350-3-nphamcs@gmail.com>
Date: Tue, 29 Apr 2025 16:38:30 -0700
From: Nhat Pham <nphamcs@...il.com>
To: linux-mm@...ck.org
Cc: akpm@...ux-foundation.org,
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Subject: [RFC PATCH v2 02/18] swapfile: rearrange functions

Rearrange some functions in preparation for the rest of the series. No
functional change intended.

Signed-off-by: Nhat Pham <nphamcs@...il.com>
---
 mm/swapfile.c | 332 +++++++++++++++++++++++++-------------------------
 1 file changed, 166 insertions(+), 166 deletions(-)

diff --git a/mm/swapfile.c b/mm/swapfile.c
index df7c4e8b089c..426674d35983 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -124,11 +124,6 @@ static struct swap_info_struct *swap_type_to_swap_info(int type)
 	return READ_ONCE(swap_info[type]); /* rcu_dereference() */
 }
 
-static inline unsigned char swap_count(unsigned char ent)
-{
-	return ent & ~SWAP_HAS_CACHE;	/* may include COUNT_CONTINUED flag */
-}
-
 /*
  * Use the second highest bit of inuse_pages counter as the indicator
  * if one swap device is on the available plist, so the atomic can
@@ -161,6 +156,11 @@ static long swap_usage_in_pages(struct swap_info_struct *si)
 /* Reclaim directly, bypass the slot cache and don't touch device lock */
 #define TTRS_DIRECT		0x8
 
+static inline unsigned char swap_count(unsigned char ent)
+{
+	return ent & ~SWAP_HAS_CACHE;	/* may include COUNT_CONTINUED flag */
+}
+
 static bool swap_is_has_cache(struct swap_info_struct *si,
 			      unsigned long offset, int nr_pages)
 {
@@ -1326,46 +1326,6 @@ static struct swap_info_struct *_swap_info_get(swp_entry_t entry)
 	return NULL;
 }
 
-static unsigned char __swap_entry_free_locked(struct swap_info_struct *si,
-					      unsigned long offset,
-					      unsigned char usage)
-{
-	unsigned char count;
-	unsigned char has_cache;
-
-	count = si->swap_map[offset];
-
-	has_cache = count & SWAP_HAS_CACHE;
-	count &= ~SWAP_HAS_CACHE;
-
-	if (usage == SWAP_HAS_CACHE) {
-		VM_BUG_ON(!has_cache);
-		has_cache = 0;
-	} else if (count == SWAP_MAP_SHMEM) {
-		/*
-		 * Or we could insist on shmem.c using a special
-		 * swap_shmem_free() and free_shmem_swap_and_cache()...
-		 */
-		count = 0;
-	} else if ((count & ~COUNT_CONTINUED) <= SWAP_MAP_MAX) {
-		if (count == COUNT_CONTINUED) {
-			if (swap_count_continued(si, offset, count))
-				count = SWAP_MAP_MAX | COUNT_CONTINUED;
-			else
-				count = SWAP_MAP_MAX;
-		} else
-			count--;
-	}
-
-	usage = count | has_cache;
-	if (usage)
-		WRITE_ONCE(si->swap_map[offset], usage);
-	else
-		WRITE_ONCE(si->swap_map[offset], SWAP_HAS_CACHE);
-
-	return usage;
-}
-
 /*
  * When we get a swap entry, if there aren't some other ways to
  * prevent swapoff, such as the folio in swap cache is locked, RCU
@@ -1432,6 +1392,46 @@ struct swap_info_struct *get_swap_device(swp_entry_t entry)
 	return NULL;
 }
 
+static unsigned char __swap_entry_free_locked(struct swap_info_struct *si,
+					      unsigned long offset,
+					      unsigned char usage)
+{
+	unsigned char count;
+	unsigned char has_cache;
+
+	count = si->swap_map[offset];
+
+	has_cache = count & SWAP_HAS_CACHE;
+	count &= ~SWAP_HAS_CACHE;
+
+	if (usage == SWAP_HAS_CACHE) {
+		VM_BUG_ON(!has_cache);
+		has_cache = 0;
+	} else if (count == SWAP_MAP_SHMEM) {
+		/*
+		 * Or we could insist on shmem.c using a special
+		 * swap_shmem_free() and free_shmem_swap_and_cache()...
+		 */
+		count = 0;
+	} else if ((count & ~COUNT_CONTINUED) <= SWAP_MAP_MAX) {
+		if (count == COUNT_CONTINUED) {
+			if (swap_count_continued(si, offset, count))
+				count = SWAP_MAP_MAX | COUNT_CONTINUED;
+			else
+				count = SWAP_MAP_MAX;
+		} else
+			count--;
+	}
+
+	usage = count | has_cache;
+	if (usage)
+		WRITE_ONCE(si->swap_map[offset], usage);
+	else
+		WRITE_ONCE(si->swap_map[offset], SWAP_HAS_CACHE);
+
+	return usage;
+}
+
 static unsigned char __swap_entry_free(struct swap_info_struct *si,
 				       swp_entry_t entry)
 {
@@ -1585,25 +1585,6 @@ void put_swap_folio(struct folio *folio, swp_entry_t entry)
 	unlock_cluster(ci);
 }
 
-void swapcache_free_entries(swp_entry_t *entries, int n)
-{
-	int i;
-	struct swap_cluster_info *ci;
-	struct swap_info_struct *si = NULL;
-
-	if (n <= 0)
-		return;
-
-	for (i = 0; i < n; ++i) {
-		si = _swap_info_get(entries[i]);
-		if (si) {
-			ci = lock_cluster(si, swp_offset(entries[i]));
-			swap_entry_range_free(si, ci, entries[i], 1);
-			unlock_cluster(ci);
-		}
-	}
-}
-
 int __swap_count(swp_entry_t entry)
 {
 	struct swap_info_struct *si = swp_swap_info(entry);
@@ -1717,57 +1698,6 @@ static bool folio_swapped(struct folio *folio)
 	return swap_page_trans_huge_swapped(si, entry, folio_order(folio));
 }
 
-static bool folio_swapcache_freeable(struct folio *folio)
-{
-	VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
-
-	if (!folio_test_swapcache(folio))
-		return false;
-	if (folio_test_writeback(folio))
-		return false;
-
-	/*
-	 * Once hibernation has begun to create its image of memory,
-	 * there's a danger that one of the calls to folio_free_swap()
-	 * - most probably a call from __try_to_reclaim_swap() while
-	 * hibernation is allocating its own swap pages for the image,
-	 * but conceivably even a call from memory reclaim - will free
-	 * the swap from a folio which has already been recorded in the
-	 * image as a clean swapcache folio, and then reuse its swap for
-	 * another page of the image.  On waking from hibernation, the
-	 * original folio might be freed under memory pressure, then
-	 * later read back in from swap, now with the wrong data.
-	 *
-	 * Hibernation suspends storage while it is writing the image
-	 * to disk so check that here.
-	 */
-	if (pm_suspended_storage())
-		return false;
-
-	return true;
-}
-
-/**
- * folio_free_swap() - Free the swap space used for this folio.
- * @folio: The folio to remove.
- *
- * If swap is getting full, or if there are no more mappings of this folio,
- * then call folio_free_swap to free its swap space.
- *
- * Return: true if we were able to release the swap space.
- */
-bool folio_free_swap(struct folio *folio)
-{
-	if (!folio_swapcache_freeable(folio))
-		return false;
-	if (folio_swapped(folio))
-		return false;
-
-	delete_from_swap_cache(folio);
-	folio_set_dirty(folio);
-	return true;
-}
-
 /**
  * free_swap_and_cache_nr() - Release reference on range of swap entries and
  *                            reclaim their cache if no more references remain.
@@ -1842,6 +1772,76 @@ void free_swap_and_cache_nr(swp_entry_t entry, int nr)
 	put_swap_device(si);
 }
 
+void swapcache_free_entries(swp_entry_t *entries, int n)
+{
+	int i;
+	struct swap_cluster_info *ci;
+	struct swap_info_struct *si = NULL;
+
+	if (n <= 0)
+		return;
+
+	for (i = 0; i < n; ++i) {
+		si = _swap_info_get(entries[i]);
+		if (si) {
+			ci = lock_cluster(si, swp_offset(entries[i]));
+			swap_entry_range_free(si, ci, entries[i], 1);
+			unlock_cluster(ci);
+		}
+	}
+}
+
+static bool folio_swapcache_freeable(struct folio *folio)
+{
+	VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
+
+	if (!folio_test_swapcache(folio))
+		return false;
+	if (folio_test_writeback(folio))
+		return false;
+
+	/*
+	 * Once hibernation has begun to create its image of memory,
+	 * there's a danger that one of the calls to folio_free_swap()
+	 * - most probably a call from __try_to_reclaim_swap() while
+	 * hibernation is allocating its own swap pages for the image,
+	 * but conceivably even a call from memory reclaim - will free
+	 * the swap from a folio which has already been recorded in the
+	 * image as a clean swapcache folio, and then reuse its swap for
+	 * another page of the image.  On waking from hibernation, the
+	 * original folio might be freed under memory pressure, then
+	 * later read back in from swap, now with the wrong data.
+	 *
+	 * Hibernation suspends storage while it is writing the image
+	 * to disk so check that here.
+	 */
+	if (pm_suspended_storage())
+		return false;
+
+	return true;
+}
+
+/**
+ * folio_free_swap() - Free the swap space used for this folio.
+ * @folio: The folio to remove.
+ *
+ * If swap is getting full, or if there are no more mappings of this folio,
+ * then call folio_free_swap to free its swap space.
+ *
+ * Return: true if we were able to release the swap space.
+ */
+bool folio_free_swap(struct folio *folio)
+{
+	if (!folio_swapcache_freeable(folio))
+		return false;
+	if (folio_swapped(folio))
+		return false;
+
+	delete_from_swap_cache(folio);
+	folio_set_dirty(folio);
+	return true;
+}
+
 #ifdef CONFIG_HIBERNATION
 
 swp_entry_t get_swap_page_of_type(int type)
@@ -1957,6 +1957,37 @@ unsigned int count_swap_pages(int type, int free)
 }
 #endif /* CONFIG_HIBERNATION */
 
+/*
+ * Scan swap_map from current position to next entry still in use.
+ * Return 0 if there are no inuse entries after prev till end of
+ * the map.
+ */
+static unsigned int find_next_to_unuse(struct swap_info_struct *si,
+					unsigned int prev)
+{
+	unsigned int i;
+	unsigned char count;
+
+	/*
+	 * No need for swap_lock here: we're just looking
+	 * for whether an entry is in use, not modifying it; false
+	 * hits are okay, and sys_swapoff() has already prevented new
+	 * allocations from this area (while holding swap_lock).
+	 */
+	for (i = prev + 1; i < si->max; i++) {
+		count = READ_ONCE(si->swap_map[i]);
+		if (count && swap_count(count) != SWAP_MAP_BAD)
+			break;
+		if ((i % LATENCY_LIMIT) == 0)
+			cond_resched();
+	}
+
+	if (i == si->max)
+		i = 0;
+
+	return i;
+}
+
 static inline int pte_same_as_swp(pte_t pte, pte_t swp_pte)
 {
 	return pte_same(pte_swp_clear_flags(pte), swp_pte);
@@ -2241,37 +2272,6 @@ static int unuse_mm(struct mm_struct *mm, unsigned int type)
 	return ret;
 }
 
-/*
- * Scan swap_map from current position to next entry still in use.
- * Return 0 if there are no inuse entries after prev till end of
- * the map.
- */
-static unsigned int find_next_to_unuse(struct swap_info_struct *si,
-					unsigned int prev)
-{
-	unsigned int i;
-	unsigned char count;
-
-	/*
-	 * No need for swap_lock here: we're just looking
-	 * for whether an entry is in use, not modifying it; false
-	 * hits are okay, and sys_swapoff() has already prevented new
-	 * allocations from this area (while holding swap_lock).
-	 */
-	for (i = prev + 1; i < si->max; i++) {
-		count = READ_ONCE(si->swap_map[i]);
-		if (count && swap_count(count) != SWAP_MAP_BAD)
-			break;
-		if ((i % LATENCY_LIMIT) == 0)
-			cond_resched();
-	}
-
-	if (i == si->max)
-		i = 0;
-
-	return i;
-}
-
 static int try_to_unuse(unsigned int type)
 {
 	struct mm_struct *prev_mm;
@@ -3525,6 +3525,26 @@ void si_swapinfo(struct sysinfo *val)
 	spin_unlock(&swap_lock);
 }
 
+struct swap_info_struct *swp_swap_info(swp_entry_t entry)
+{
+	return swap_type_to_swap_info(swp_type(entry));
+}
+
+/*
+ * out-of-line methods to avoid include hell.
+ */
+struct address_space *swapcache_mapping(struct folio *folio)
+{
+	return swp_swap_info(folio->swap)->swap_file->f_mapping;
+}
+EXPORT_SYMBOL_GPL(swapcache_mapping);
+
+pgoff_t __folio_swap_cache_index(struct folio *folio)
+{
+	return swap_cache_index(folio->swap);
+}
+EXPORT_SYMBOL_GPL(__folio_swap_cache_index);
+
 /*
  * Verify that nr swap entries are valid and increment their swap map counts.
  *
@@ -3658,26 +3678,6 @@ void swapcache_clear(struct swap_info_struct *si, swp_entry_t entry, int nr)
 	cluster_swap_free_nr(si, offset, nr, SWAP_HAS_CACHE);
 }
 
-struct swap_info_struct *swp_swap_info(swp_entry_t entry)
-{
-	return swap_type_to_swap_info(swp_type(entry));
-}
-
-/*
- * out-of-line methods to avoid include hell.
- */
-struct address_space *swapcache_mapping(struct folio *folio)
-{
-	return swp_swap_info(folio->swap)->swap_file->f_mapping;
-}
-EXPORT_SYMBOL_GPL(swapcache_mapping);
-
-pgoff_t __folio_swap_cache_index(struct folio *folio)
-{
-	return swap_cache_index(folio->swap);
-}
-EXPORT_SYMBOL_GPL(__folio_swap_cache_index);
-
 /*
  * add_swap_count_continuation - called when a swap count is duplicated
  * beyond SWAP_MAP_MAX, it allocates a new page and links that to the entry's
-- 
2.47.1

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