mm: swap: rename __swap_[entry/entries]_free[_locked] to swap_[entry/entries]_put...

Patch series "Minor cleanups and improvements to swap freeing code", v4.

This series contains some cleanups and improvements which are made
during learning swapfile. Here is a summary of the changes:

1. Function naming improvments.

  - Use "put" instead of "free" to name functions which only do actual
    free when count drops to zero.

  - Use "entry" to name function only frees one swap slot.  Use
    "entries" to name function could may free multi swap slots within one
    cluster.  Use "_nr" suffix to name function which could free multi
    swap slots spanning cross multi clusters.

2. Eliminate the need to set swap slot to intermediate SWAP_HAS_CACHE
   value before do actual free by using swap_entry_range_free()

3. Add helpers swap_entries_put_map() and swap_entries_put_cache() as
   a general-purpose routine to free swap entries within a single cluster
   which will try batch-remove first and fallback to put eatch entry
   indvidually with cluster lock acquired/released only once.  By using
   these helpers, we could remove repeated code, levarage batch-remove in
   more cases and aoivd to acquire/release cluster lock for each single
   swap entry.

This patch (of 8):

In __swap_entry_free[_locked] and __swap_entries_free, we decrease count
first and only free swap entry if count drops to zero.  This behavior is
more akin to a put() operation rather than a free() operation.  Therefore,
rename these functions with "put" instead of "free".  Additionally, add
"_nr" suffix to swap_entries_put to indicate the input range may span swap
clusters.

Link: https://lkml.kernel.org/r/20250325162528.68385-1-shikemeng@huaweicloud.com
Link: https://lkml.kernel.org/r/20250325162528.68385-2-shikemeng@huaweicloud.com
Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
Reviewed-by: Tim Chen <tim.c.chen@linux.intel.com>
Reviewed-by: Baoquan He <bhe@redhat.com>
Cc: Kairui Song <kasong@tencent.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/swapfile.c b/mm/swapfile.c
index f214843612dc32e63fe681489dbbb56572f3bc23..ea01cf05b0cb989defd10ef3d45c5967ec18f6a9 100644 (file)
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1355,9 +1355,9 @@ out:
        return NULL;
 }
 
-static unsigned char __swap_entry_free_locked(struct swap_info_struct *si,
-                                             unsigned long offset,
-                                             unsigned char usage)
+static unsigned char swap_entry_put_locked(struct swap_info_struct *si,
+                                          unsigned long offset,
+                                          unsigned char usage)
 {
        unsigned char count;
        unsigned char has_cache;
@@ -1461,15 +1461,15 @@ put_out:
        return NULL;
 }
 
-static unsigned char __swap_entry_free(struct swap_info_struct *si,
-                                      swp_entry_t entry)
+static unsigned char swap_entry_put(struct swap_info_struct *si,
+                                   swp_entry_t entry)
 {
        struct swap_cluster_info *ci;
        unsigned long offset = swp_offset(entry);
        unsigned char usage;
 
        ci = lock_cluster(si, offset);
-       usage = __swap_entry_free_locked(si, offset, 1);
+       usage = swap_entry_put_locked(si, offset, 1);
        if (!usage)
                swap_entry_range_free(si, ci, swp_entry(si->type, offset), 1);
        unlock_cluster(ci);
@@ -1477,8 +1477,8 @@ static unsigned char __swap_entry_free(struct swap_info_struct *si,
        return usage;
 }
 
-static bool __swap_entries_free(struct swap_info_struct *si,
-               swp_entry_t entry, int nr)
+static bool swap_entries_put_nr(struct swap_info_struct *si,
+                               swp_entry_t entry, int nr)
 {
        unsigned long offset = swp_offset(entry);
        unsigned int type = swp_type(entry);
@@ -1509,7 +1509,7 @@ static bool __swap_entries_free(struct swap_info_struct *si,
 fallback:
        for (i = 0; i < nr; i++) {
                if (data_race(si->swap_map[offset + i])) {
-                       count = __swap_entry_free(si, swp_entry(type, offset + i));
+                       count = swap_entry_put(si, swp_entry(type, offset + i));
                        if (count == SWAP_HAS_CACHE)
                                has_cache = true;
                } else {
@@ -1560,7 +1560,7 @@ static void cluster_swap_free_nr(struct swap_info_struct *si,
 
        ci = lock_cluster(si, offset);
        do {
-               if (!__swap_entry_free_locked(si, offset, usage))
+               if (!swap_entry_put_locked(si, offset, usage))
                        swap_entry_range_free(si, ci, swp_entry(si->type, offset), 1);
        } while (++offset < end);
        unlock_cluster(ci);
@@ -1607,7 +1607,7 @@ void put_swap_folio(struct folio *folio, swp_entry_t entry)
                swap_entry_range_free(si, ci, entry, size);
        else {
                for (int i = 0; i < size; i++, entry.val++) {
-                       if (!__swap_entry_free_locked(si, offset + i, SWAP_HAS_CACHE))
+                       if (!swap_entry_put_locked(si, offset + i, SWAP_HAS_CACHE))
                                swap_entry_range_free(si, ci, entry, 1);
                }
        }
@@ -1806,7 +1806,7 @@ void free_swap_and_cache_nr(swp_entry_t entry, int nr)
        /*
         * First free all entries in the range.
         */
-       any_only_cache = __swap_entries_free(si, entry, nr);
+       any_only_cache = swap_entries_put_nr(si, entry, nr);
 
        /*
         * Short-circuit the below loop if none of the entries had their
@@ -1819,7 +1819,7 @@ void free_swap_and_cache_nr(swp_entry_t entry, int nr)
         * Now go back over the range trying to reclaim the swap cache. This is
         * more efficient for large folios because we will only try to reclaim
         * the swap once per folio in the common case. If we do
-        * __swap_entry_free() and __try_to_reclaim_swap() in the same loop, the
+        * swap_entry_put() and __try_to_reclaim_swap() in the same loop, the
         * latter will get a reference and lock the folio for every individual
         * page but will only succeed once the swap slot for every subpage is
         * zero.
@@ -3789,7 +3789,7 @@ outer:
  * into, carry if so, or else fail until a new continuation page is allocated;
  * when the original swap_map count is decremented from 0 with continuation,
  * borrow from the continuation and report whether it still holds more.
- * Called while __swap_duplicate() or caller of __swap_entry_free_locked()
+ * Called while __swap_duplicate() or caller of swap_entry_put_locked()
  * holds cluster lock.
  */
 static bool swap_count_continued(struct swap_info_struct *si,