[v4,0/8] Minor cleanups and improvements to swap freeing code

Message

Kemeng Shi March 25, 2025, 4:25 p.m. UTC

v3->v4:
-Collect RVB from Baoquan
-Grammatical correctness and typo fix in changelog.

v2->v3:
-Extent VM_BUG_ON instead of remove it
-Keep bracket for more readability
-Collect RVB from Tim for rest part

v1->v2:
-Collect RVB from Tim
-Drop patch to factor out __swap_entry_free()
-Improve changelog and add more comment.
-Avoid unneeded lock re-aquire

Hi All,
This series contains some cleanups and improvements which are made
during learning swapfile. Here is a summary of the changes:
1. Function nameing 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.

Kemeng Shi (8):
  mm: swap: rename __swap_[entry/entries]_free[_locked] to
    swap_[entry/entries]_put[_locked]
  mm: swap: enable swap_entry_range_free() to drop any kind of last ref
  mm: swap: use swap_entries_free() to free swap entry in
    swap_entry_put_locked()
  mm: swap: use swap_entries_free() drop last ref count in
    swap_entries_put_nr()
  mm: swap: drop last SWAP_MAP_SHMEM flag in batch in
    swap_entries_put_nr()
  mm: swap: free each cluster individually in swap_entries_put_map_nr()
  mm: swap: factor out helper to drop cache of entries within a single
    cluster
  mm: swap: replace cluster_swap_free_nr() with
    swap_entries_put_[map/cache]()

 mm/swapfile.c | 165 +++++++++++++++++++++++++-------------------------
 1 file changed, 83 insertions(+), 82 deletions(-)