[PATCH v2 10/11] mm/memcg: remove no longer used swap cgroup array

Kairui Song via B4 Relay
2026-04-16T18:34:43Z

Now all swap cgroup records are stored in the swap cluster directly,
no more need for a static array for that.

Signed-off-by: Kairui Song <kasong@tencent.com>
---
MAINTAINERS | 1 -
include/linux/swap_cgroup.h | 47 ------------
mm/Makefile | 3 -
mm/internal.h | 1 -
mm/memcontrol-v1.c | 1 -
mm/memcontrol.c | 1 -
mm/swap_cgroup.c | 172 --------------------------------------------
mm/swapfile.c | 8 ---
8 files changed, 234 deletions(-)

diff --git a/MAINTAINERS b/MAINTAINERS
index ab54a9c77603..b34f39cbe3ec 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -6567,7 +6567,6 @@ F: mm/memcontrol.c
F: mm/memcontrol-v1.c
F: mm/memcontrol-v1.h
F: mm/page_counter.c
-F: mm/swap_cgroup.c
F: samples/cgroup/*
F: tools/testing/selftests/cgroup/memcg_protection.m
F: tools/testing/selftests/cgroup/test_hugetlb_memcg.c
diff --git a/include/linux/swap_cgroup.h b/include/linux/swap_cgroup.h
deleted file mode 100644
index 91cdf12190a0..000000000000
--- a/include/linux/swap_cgroup.h
+++ /dev/null
@@ -1,47 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0 */
-#ifndef __LINUX_SWAP_CGROUP_H
-#define __LINUX_SWAP_CGROUP_H
-
-#include <linux/swap.h>
-
-#if defined(CONFIG_MEMCG) && defined(CONFIG_SWAP)
-
-extern void swap_cgroup_record(struct folio *folio, unsigned short id, swp_entry_t ent);
-extern unsigned short swap_cgroup_clear(swp_entry_t ent, unsigned int nr_ents);
-extern unsigned short lookup_swap_cgroup_id(swp_entry_t ent);
-extern int swap_cgroup_swapon(int type, unsigned long max_pages);
-extern void swap_cgroup_swapoff(int type);
-
-#else
-
-static inline
-void swap_cgroup_record(struct folio *folio, unsigned short id, swp_entry_t ent)
-{
-}
-
-static inline
-unsigned short swap_cgroup_clear(swp_entry_t ent, unsigned int nr_ents)
-{
- return 0;
-}
-
-static inline
-unsigned short lookup_swap_cgroup_id(swp_entry_t ent)
-{
- return 0;
-}
-
-static inline int
-swap_cgroup_swapon(int type, unsigned long max_pages)
-{
- return 0;
-}
-
-static inline void swap_cgroup_swapoff(int type)
-{
- return;
-}
-
-#endif
-
-#endif /* __LINUX_SWAP_CGROUP_H */
diff --git a/mm/Makefile b/mm/Makefile
index 8ad2ab08244e..eff9f9e7e061 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -103,9 +103,6 @@ obj-$(CONFIG_PAGE_COUNTER) += page_counter.o
obj-$(CONFIG_LIVEUPDATE_MEMFD) += memfd_luo.o
obj-$(CONFIG_MEMCG_V1) += memcontrol-v1.o
obj-$(CONFIG_MEMCG) += memcontrol.o vmpressure.o
-ifdef CONFIG_SWAP
-obj-$(CONFIG_MEMCG) += swap_cgroup.o
-endif
ifdef CONFIG_BPF_SYSCALL
obj-$(CONFIG_MEMCG) += bpf_memcontrol.o
endif
diff --git a/mm/internal.h b/mm/internal.h
index 32de9f3a9fa0..164c7f0a6a98 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -17,7 +17,6 @@
#include <linux/rmap.h>
#include <linux/swap.h>
#include <linux/leafops.h>
-#include <linux/swap_cgroup.h>
#include <linux/tracepoint-defs.h>

/* Internal core VMA manipulation functions. */
diff --git a/mm/memcontrol-v1.c b/mm/memcontrol-v1.c
index ff49337a61a3..c2a39ae1fd69 100644
--- a/mm/memcontrol-v1.c
+++ b/mm/memcontrol-v1.c
@@ -5,7 +5,6 @@
#include <linux/mm_inline.h>
#include <linux/pagewalk.h>
#include <linux/backing-dev.h>
-#include <linux/swap_cgroup.h>
#include <linux/eventfd.h>
#include <linux/poll.h>
#include <linux/sort.h>
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 43a7b25da37e..493aff40df0c 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -54,7 +54,6 @@
#include <linux/vmpressure.h>
#include <linux/memremap.h>
#include <linux/mm_inline.h>
-#include <linux/swap_cgroup.h>
#include <linux/cpu.h>
#include <linux/oom.h>
#include <linux/lockdep.h>
diff --git a/mm/swap_cgroup.c b/mm/swap_cgroup.c
deleted file mode 100644
index de779fed8c21..000000000000
--- a/mm/swap_cgroup.c
+++ /dev/null
@@ -1,172 +0,0 @@
-// SPDX-License-Identifier: GPL-2.0
-#include <linux/swap_cgroup.h>
-#include <linux/vmalloc.h>
-#include <linux/mm.h>
-
-#include <linux/swapops.h> /* depends on mm.h include */
-
-static DEFINE_MUTEX(swap_cgroup_mutex);
-
-/* Pack two cgroup id (short) of two entries in one swap_cgroup (atomic_t) */
-#define ID_PER_SC (sizeof(struct swap_cgroup) / sizeof(unsigned short))
-#define ID_SHIFT (BITS_PER_TYPE(unsigned short))
-#define ID_MASK (BIT(ID_SHIFT) - 1)
-struct swap_cgroup {
- atomic_t ids;
-};
-
-struct swap_cgroup_ctrl {
- struct swap_cgroup *map;
-};
-
-static struct swap_cgroup_ctrl swap_cgroup_ctrl[MAX_SWAPFILES];
-
-static unsigned short __swap_cgroup_id_lookup(struct swap_cgroup *map,
- pgoff_t offset)
-{
- unsigned int shift = (offset % ID_PER_SC) * ID_SHIFT;
- unsigned int old_ids = atomic_read(&map[offset / ID_PER_SC].ids);
-
- BUILD_BUG_ON(!is_power_of_2(ID_PER_SC));
- BUILD_BUG_ON(sizeof(struct swap_cgroup) != sizeof(atomic_t));
-
- return (old_ids >> shift) & ID_MASK;
-}
-
-static unsigned short __swap_cgroup_id_xchg(struct swap_cgroup *map,
- pgoff_t offset,
- unsigned short new_id)
-{
- unsigned short old_id;
- struct swap_cgroup *sc = &map[offset / ID_PER_SC];
- unsigned int shift = (offset % ID_PER_SC) * ID_SHIFT;
- unsigned int new_ids, old_ids = atomic_read(&sc->ids);
-
- do {
- old_id = (old_ids >> shift) & ID_MASK;
- new_ids = (old_ids & ~(ID_MASK << shift));
- new_ids |= ((unsigned int)new_id) << shift;
- } while (!atomic_try_cmpxchg(&sc->ids, &old_ids, new_ids));
-
- return old_id;
-}
-
-/**
- * swap_cgroup_record - record mem_cgroup for a set of swap entries.
- * These entries must belong to one single folio, and that folio
- * must be being charged for swap space (swap out), and these
- * entries must not have been charged
- *
- * @folio: the folio that the swap entry belongs to
- * @id: mem_cgroup ID to be recorded
- * @ent: the first swap entry to be recorded
- */
-void swap_cgroup_record(struct folio *folio, unsigned short id,
- swp_entry_t ent)
-{
- unsigned int nr_ents = folio_nr_pages(folio);
- struct swap_cgroup *map;
- pgoff_t offset, end;
- unsigned short old;
-
- offset = swp_offset(ent);
- end = offset + nr_ents;
- map = swap_cgroup_ctrl[swp_type(ent)].map;
-
- do {
- old = __swap_cgroup_id_xchg(map, offset, id);
- VM_BUG_ON(old);
- } while (++offset != end);
-}
-
-/**
- * swap_cgroup_clear - clear mem_cgroup for a set of swap entries.
- * These entries must be being uncharged from swap. They either
- * belongs to one single folio in the swap cache (swap in for
- * cgroup v1), or no longer have any users (slot freeing).
- *
- * @ent: the first swap entry to be recorded into
- * @nr_ents: number of swap entries to be recorded
- *
- * Returns the existing old value.
- */
-unsigned short swap_cgroup_clear(swp_entry_t ent, unsigned int nr_ents)
-{
- pgoff_t offset, end;
- struct swap_cgroup *map;
- unsigned short old, iter = 0;
-
- offset = swp_offset(ent);
- end = offset + nr_ents;
- map = swap_cgroup_ctrl[swp_type(ent)].map;
-
- do {
- old = __swap_cgroup_id_xchg(map, offset, 0);
- if (!iter)
- iter = old;
- VM_BUG_ON(iter != old);
- } while (++offset != end);
-
- return old;
-}
-
-/**
- * lookup_swap_cgroup_id - lookup mem_cgroup id tied to swap entry
- * @ent: swap entry to be looked up.
- *
- * Returns ID of mem_cgroup at success. 0 at failure. (0 is invalid ID)
- */
-unsigned short lookup_swap_cgroup_id(swp_entry_t ent)
-{
- struct swap_cgroup_ctrl *ctrl;
-
- if (mem_cgroup_disabled())
- return 0;
-
- ctrl = &swap_cgroup_ctrl[swp_type(ent)];
- return __swap_cgroup_id_lookup(ctrl->map, swp_offset(ent));
-}
-
-int swap_cgroup_swapon(int type, unsigned long max_pages)
-{
- struct swap_cgroup *map;
- struct swap_cgroup_ctrl *ctrl;
-
- if (mem_cgroup_disabled())
- return 0;
-
- BUILD_BUG_ON(sizeof(unsigned short) * ID_PER_SC !=
- sizeof(struct swap_cgroup));
- map = vzalloc(DIV_ROUND_UP(max_pages, ID_PER_SC) *
- sizeof(struct swap_cgroup));
- if (!map)
- goto nomem;
-
- ctrl = &swap_cgroup_ctrl[type];
- mutex_lock(&swap_cgroup_mutex);
- ctrl->map = map;
- mutex_unlock(&swap_cgroup_mutex);
-
- return 0;
-nomem:
- pr_info("couldn't allocate enough memory for swap_cgroup\n");
- pr_info("swap_cgroup can be disabled by swapaccount=0 boot option\n");
- return -ENOMEM;
-}
-
-void swap_cgroup_swapoff(int type)
-{
- struct swap_cgroup *map;
- struct swap_cgroup_ctrl *ctrl;
-
- if (mem_cgroup_disabled())
- return;
-
- mutex_lock(&swap_cgroup_mutex);
- ctrl = &swap_cgroup_ctrl[type];
- map = ctrl->map;
- ctrl->map = NULL;
- mutex_unlock(&swap_cgroup_mutex);
-
- vfree(map);
-}
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 5511cdbd2ccf..0753a62ebc25 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -45,7 +45,6 @@

#include <asm/tlbflush.h>
#include <linux/leafops.h>
-#include <linux/swap_cgroup.h>
#include "swap_table.h"
#include "internal.h"
#include "swap.h"
@@ -3173,8 +3172,6 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
p->global_cluster = NULL;
kvfree(zeromap);
free_swap_cluster_info(cluster_info, maxpages);
- /* Destroy swap account information */
- swap_cgroup_swapoff(p->type);

inode = mapping->host;

@@ -3705,10 +3702,6 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
if (error)
goto bad_swap_unlock_inode;

- error = swap_cgroup_swapon(si->type, maxpages);
- if (error)
- goto bad_swap_unlock_inode;
-
/*
* Use kvmalloc_array instead of bitmap_zalloc as the allocation order might
* be above MAX_PAGE_ORDER incase of a large swap file.
@@ -3819,7 +3812,6 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
si->global_cluster = NULL;
inode = NULL;
destroy_swap_extents(si, swap_file);
- swap_cgroup_swapoff(si->type);
free_swap_cluster_info(si->cluster_info, si->max);
si->cluster_info = NULL;
kvfree(si->zeromap);

--
2.53.0