[PATCH v6 11/12] mm, swap: add vmstat and memcg counters for vswap
From: Nhat Pham
Date: Wed Oct 21 2026 - 02:23:27 EST
Add nr_vswap to /proc/vmstat and vswap to cgroup's memory.stat to report
virtual swap usage.
These counters help diagnose swapping issues. Userspace can also use
vswap as a component of a workload's logical memory footprint when
making policy decisions.
Suggested-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Signed-off-by: Nhat Pham <nphamcs@xxxxxxxxx>
---
.../admin-guide/cgroup-v1/memory.rst | 1 +
Documentation/admin-guide/cgroup-v2.rst | 3 +++
include/linux/memcontrol.h | 1 +
include/linux/swap.h | 1 +
include/linux/vmstat.h | 3 +++
mm/memcontrol-v1.c | 6 +++++-
mm/memcontrol.c | 20 +++++++++++++++----
mm/swapfile.c | 10 +++++++---
mm/vmstat.c | 6 ++++++
9 files changed, 43 insertions(+), 8 deletions(-)
diff --git a/Documentation/admin-guide/cgroup-v1/memory.rst b/Documentation/admin-guide/cgroup-v1/memory.rst
index 2a67356d25a0..8ca9ef2bca9f 100644
--- a/Documentation/admin-guide/cgroup-v1/memory.rst
+++ b/Documentation/admin-guide/cgroup-v1/memory.rst
@@ -555,6 +555,7 @@ memory.stat file includes following statistics:
cgroup.
swap # of bytes of physical swap usage
swapcached # of bytes of swap cached in memory
+ vswap # of bytes of virtual swap usage
dirty # of bytes that are waiting to get written back to the disk.
writeback # of bytes of file/anon cache that are queued for syncing to
disk.
diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
index 623d29ea8c41..b1f97a61a1dc 100644
--- a/Documentation/admin-guide/cgroup-v2.rst
+++ b/Documentation/admin-guide/cgroup-v2.rst
@@ -1633,6 +1633,9 @@ The following nested keys are defined.
against memory usage, and against swap usage when the swap
entry has physical backing.
+ vswap
+ Amount of virtual swap usage.
+
anon_thp
Amount of memory used in anonymous mappings backed by
transparent hugepages
diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index b9072a3c9a2a..99beb676d8e7 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -41,6 +41,7 @@ enum memcg_stat_item {
MEMCG_ZSWAP_B,
MEMCG_ZSWAPPED,
MEMCG_ZSWAP_INCOMP,
+ MEMCG_VSWAP,
MEMCG_NR_STAT,
};
diff --git a/include/linux/swap.h b/include/linux/swap.h
index a05189c92dae..891442264ca9 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -371,6 +371,7 @@ bool current_is_kswapd(void);
#ifdef CONFIG_SWAP
bool mem_cgroup_can_vswap(struct mem_cgroup *memcg);
+unsigned long vswap_usage_in_pages(void);
int add_swap_extent(struct swap_info_struct *sis, unsigned long start_page,
unsigned long nr_pages, sector_t start_block);
diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h
index 5b31d8e7ae40..37aff1ffac08 100644
--- a/include/linux/vmstat.h
+++ b/include/linux/vmstat.h
@@ -33,6 +33,9 @@ enum vm_stat_item {
NR_DIRTY_BG_THRESHOLD,
NR_MEMMAP_PAGES, /* page metadata allocated through buddy allocator */
NR_MEMMAP_BOOT_PAGES, /* page metadata allocated through boot allocator */
+#ifdef CONFIG_SWAP
+ NR_VSWAP, /* pages occupying a virtual swap slot */
+#endif
NR_VM_STAT_ITEMS,
};
diff --git a/mm/memcontrol-v1.c b/mm/memcontrol-v1.c
index 4e4946728db5..8fa7b2fb109d 100644
--- a/mm/memcontrol-v1.c
+++ b/mm/memcontrol-v1.c
@@ -300,7 +300,9 @@ void __memcg1_swapout(struct folio *folio, struct swap_cluster_info *ci)
*/
nr_entries = folio_nr_pages(folio);
private_id = mem_cgroup_private_id_get(memcg, nr_entries);
- if (!is_vswap_entry(folio->swap))
+ if (is_vswap_entry(folio->swap))
+ mod_memcg_state(memcg, MEMCG_VSWAP, nr_entries);
+ else
mod_memcg_state(memcg, MEMCG_SWAP, nr_entries);
__swap_cgroup_set(ci, swp_cluster_offset(folio->swap), nr_entries, private_id);
@@ -1842,6 +1844,7 @@ static const unsigned int memcg1_stats[] = {
#ifdef CONFIG_SWAP
MEMCG_SWAP,
NR_SWAPCACHE,
+ MEMCG_VSWAP,
#endif
};
@@ -1860,6 +1863,7 @@ static const char *const memcg1_stat_names[] = {
#ifdef CONFIG_SWAP
"swap",
"swapcached",
+ "vswap",
#endif
};
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index e2aa75a292ed..eedaa094a867 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -66,6 +66,7 @@
#include "internal.h"
#include "swap.h"
#include "swap_table.h"
+#include "vswap.h"
#include <net/sock.h>
#include <net/ip.h>
#include "slab.h"
@@ -459,6 +460,7 @@ static const unsigned int memcg_stat_items[] = {
MEMCG_ZSWAP_B,
MEMCG_ZSWAPPED,
MEMCG_ZSWAP_INCOMP,
+ MEMCG_VSWAP,
};
#define NR_MEMCG_NODE_STAT_ITEMS ARRAY_SIZE(memcg_node_stat_items)
@@ -1628,6 +1630,7 @@ static const struct memory_stat memory_stats[] = {
{ "file_writeback", NR_WRITEBACK },
#ifdef CONFIG_SWAP
{ "swapcached", NR_SWAPCACHE },
+ { "vswap", MEMCG_VSWAP },
#endif
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
{ "anon_thp", NR_ANON_THPS },
@@ -6004,6 +6007,7 @@ unsigned short __mem_cgroup_swap_get(struct folio *folio)
unsigned int nr_pages = folio_nr_pages(folio);
struct mem_cgroup *memcg;
struct obj_cgroup *objcg;
+ unsigned short id;
if (do_memsw_account())
return 0;
@@ -6020,7 +6024,12 @@ unsigned short __mem_cgroup_swap_get(struct folio *folio)
return 0;
}
- return mem_cgroup_private_id_get(memcg, nr_pages);
+ id = mem_cgroup_private_id_get(memcg, nr_pages);
+ if (is_vswap_entry(folio->swap)) {
+ memcg = obj_cgroup_memcg(obj_cgroup_from_private_id(id));
+ mod_memcg_state(memcg, MEMCG_VSWAP, nr_pages);
+ }
+ return id;
}
/**
@@ -6109,7 +6118,7 @@ void __mem_cgroup_swap_uncharge(unsigned short id, unsigned int nr_pages)
* __mem_cgroup_swap_put - drop the private ID refs taken for swap slots
* @id: the pinned private ID
* @nr_pages: number of refs to drop
- * @is_vswap: whether the released swap slots are virtual
+ * @is_vswap: release virtual-swap accounting along with the refs
*/
void __mem_cgroup_swap_put(unsigned short id, unsigned int nr_pages,
bool is_vswap)
@@ -6117,9 +6126,12 @@ void __mem_cgroup_swap_put(unsigned short id, unsigned int nr_pages,
struct mem_cgroup *memcg;
guard(rcu)();
- if (do_memsw_account() && !is_vswap) {
+ if (is_vswap || do_memsw_account()) {
memcg = obj_cgroup_memcg(obj_cgroup_from_private_id(id));
- mod_memcg_state(memcg, MEMCG_SWAP, -nr_pages);
+ if (is_vswap)
+ mod_memcg_state(memcg, MEMCG_VSWAP, -nr_pages);
+ else
+ mod_memcg_state(memcg, MEMCG_SWAP, -nr_pages);
}
mem_cgroup_private_id_put(id, nr_pages);
}
diff --git a/mm/swapfile.c b/mm/swapfile.c
index e95f2441fdd7..fe5460d15f55 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -2612,9 +2612,8 @@ static void __swap_cluster_free_phys_backing(struct swap_info_struct *psi,
}
/*
- * Release the cgroup accounting of a batch of freed slots. For vswap the
- * physical swap was already uncharged by __vswap_release_backing(), so only
- * the ID ref is left to drop.
+ * Release cgroup accounting for freed swap slots. Physical backing of
+ * vswap entries was already uncharged by __vswap_release_backing().
*/
static void memcg_swap_free(unsigned short id, unsigned int nr, bool is_vswap)
{
@@ -4922,6 +4921,11 @@ early_param("vswap", early_vswap);
/* vswap does no IO on its own. */
static const struct swap_ops vswap_ops = { };
+unsigned long vswap_usage_in_pages(void)
+{
+ return vswap_is_enabled() ? swap_usage_in_pages(vswap_si) : 0;
+}
+
static int vswap_used_get(void *data, u64 *val)
{
*val = swap_usage_in_pages(vswap_si);
diff --git a/mm/vmstat.c b/mm/vmstat.c
index a3e809c57f29..b7077a6f244d 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1320,6 +1320,9 @@ const char * const vmstat_text[] = {
[I(NR_DIRTY_BG_THRESHOLD)] = "nr_dirty_background_threshold",
[I(NR_MEMMAP_PAGES)] = "nr_memmap_pages",
[I(NR_MEMMAP_BOOT_PAGES)] = "nr_memmap_boot_pages",
+#ifdef CONFIG_SWAP
+ [I(NR_VSWAP)] = "nr_vswap",
+#endif
#undef I
#if defined(CONFIG_VM_EVENT_COUNTERS)
@@ -1936,6 +1939,9 @@ static void *vmstat_start(struct seq_file *m, loff_t *pos)
v + NR_DIRTY_THRESHOLD);
v[NR_MEMMAP_PAGES] = atomic_long_read(&nr_memmap_pages);
v[NR_MEMMAP_BOOT_PAGES] = atomic_long_read(&nr_memmap_boot_pages);
+#ifdef CONFIG_SWAP
+ v[NR_VSWAP] = vswap_usage_in_pages();
+#endif
v += NR_VM_STAT_ITEMS;
#ifdef CONFIG_VM_EVENT_COUNTERS
--
2.53.0-Meta