mm: rename swap.c to folio.c

Rename mm/swap.c to mm/folio.c so the filename better matches the code's
main responsibility.

This keeps the implementation split from swap-specific code without
changing the published LRU helper interfaces.

Update MAINTAINERS and the remaining mm/swap.c documentation references
after the rename.

[wujianyue000@gmail.com: MAINTAINERS: move mm/folio.c to MM CORE]
  Link: https://lore.kernel.org/20260804111109.393127-1-wujianyue000@gmail.com
Link: https://lore.kernel.org/20260708-ch-swap-series-plus-folio-lru-cleanup-v9-2-2bc72b4f8730@gmail.com
Signed-off-by: Jianyue Wu <wujianyue000@gmail.com>
Suggested-by: Baoquan He <bhe@redhat.com>
Suggested-by: David Hildenbrand <david@kernel.org>
Suggested-by: Matthew Wilcox <willy@infradead.org>
Reviewed-by: Lorenzo Stoakes <ljs@kernel.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Chris Li <chrisl@kernel.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Kairui Song <kasong@tencent.com>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Wei Xu <weixugc@google.com>
Cc: Yuanchu Xie <yuanchu@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Documentation/admin-guide/sysctl/vm.rst

@@ -19,9 +19,6 @@ The files in this directory can be used to tune the operation
 of the virtual memory (VM) subsystem of the Linux kernel and
 the writeout of dirty data to disk.
 
-Default values and initialization routines for most of these
-files can be found in mm/swap.c.
-
 Currently, these files are in /proc/sys/vm:
 
 - admin_reserve_kbytes

Documentation/core-api/mm-api.rst

@@ -118,7 +118,7 @@ More Memory Management Functions
 .. #kernel-doc:: mm/hmm.c (build warnings)
 .. kernel-doc:: mm/memremap.c
 .. kernel-doc:: mm/hugetlb.c
-.. kernel-doc:: mm/swap.c
+.. kernel-doc:: mm/folio.c
 .. kernel-doc:: mm/memcontrol.c
 .. #kernel-doc:: mm/memory-tiers.c (build warnings)
 .. kernel-doc:: mm/shmem.c

MAINTAINERS

@@ -16988,6 +16988,7 @@ F:	kernel/fork.c
 F:	mm/Kconfig
 F:	mm/debug.c
 F:	mm/folio-compat.c
+F:	mm/folio.c
 F:	mm/highmem.c
 F:	mm/init-mm.c
 F:	mm/internal.h
@@ -17088,7 +17089,6 @@ F:	Documentation/admin-guide/mm/multigen_lru.rst
 F:	Documentation/mm/multigen_lru.rst
 F:	include/linux/mm_inline.h
 F:	include/linux/mmzone.h
-F:	mm/swap.c
 F:	mm/vmscan.c
 F:	mm/workingset.c
 
@@ -17240,7 +17240,6 @@ F:	include/linux/swap.h
 F:	include/linux/swapfile.h
 F:	include/linux/swapops.h
 F:	mm/page_io.c
-F:	mm/swap.c
 F:	mm/swap.h
 F:	mm/swap_table.h
 F:	mm/swap_state.c

mm/Makefile

@@ -50,7 +50,7 @@ endif
 
 obj-y			:= filemap.o mempool.o oom_kill.o fadvise.o \
 			   maccess.o page-writeback.o folio-compat.o \
-			   readahead.o swap.o truncate.o vmscan.o shrinker.o \
+			   readahead.o folio.o truncate.o vmscan.o shrinker.o \
 			   shmem.o util.o mmzone.o vmstat.o backing-dev.o \
 			   mm_init.o percpu.o slab_common.o \
 			   compaction.o show_mem.o \

mm/folio.c

@@ -1,17 +1,13 @@
 // SPDX-License-Identifier: GPL-2.0-only
 /*
- *  linux/mm/swap.c
+ *  linux/mm/folio.c
  *
  *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
  */
 
 /*
- * This file contains the default values for the operation of the
- * Linux VM subsystem. Fine-tuning documentation can be found in
- * Documentation/admin-guide/sysctl/vm.rst.
- * Started 18.12.91
- * Swap aging added 23.2.95, Stephen Tweedie.
- * Buffermem limits added 12.3.98, Rik van Riel.
+ * Folio LRU helpers: add/remove folios from LRU lists, batching,
+ * activation/deactivation, and page cache release paths.
  */
 
 #include <linux/mm.h>