From: Ye Liu <ye.liu@linux.dev>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
"Rafael J. Wysocki" <rafael@kernel.org>,
Danilo Krummrich <dakr@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
David Hildenbrand <david@kernel.org>,
Lorenzo Stoakes <ljs@kernel.org>
Cc: Ye Liu <liuye@kylinos.cn>, "Liam R. Howlett" <liam@infradead.org>,
Vlastimil Babka <vbabka@kernel.org>,
Mike Rapoport <rppt@kernel.org>,
Suren Baghdasaryan <surenb@google.com>,
Michal Hocko <mhocko@suse.com>, Kairui Song <kasong@tencent.com>,
Qi Zheng <qi.zheng@linux.dev>,
Shakeel Butt <shakeel.butt@linux.dev>,
Barry Song <baohua@kernel.org>,
Axel Rasmussen <axelrasmussen@google.com>,
Yuanchu Xie <yuanchu@google.com>, Wei Xu <weixugc@google.com>,
Zi Yan <ziy@nvidia.com>,
Baolin Wang <baolin.wang@linux.alibaba.com>,
Nico Pache <npache@redhat.com>,
Ryan Roberts <ryan.roberts@arm.com>, Dev Jain <dev.jain@arm.com>,
Lance Yang <lance.yang@linux.dev>,
Usama Arif <usama.arif@linux.dev>,
driver-core@lists.linux.dev, linux-kernel@vger.kernel.org,
linux-mm@kvack.org, linux-fsdevel@vger.kernel.org
Subject: [PATCH] mm/thp: expose deferred split folio memory usage in meminfo
Date: Fri, 17 Jul 2026 14:30:22 +0800 [thread overview]
Message-ID: <20260717063025.168436-1-ye.liu@linux.dev> (raw)
From: Ye Liu <liuye@kylinos.cn>
Folios on the deferred split list hold physical memory that is
invisible in meminfo. When a THP becomes partially mapped, the
unmapped pages are removed from AnonPages but remain physically
allocated until the shrinker splits the folio. This creates a
memory accounting gap where used memory cannot be attributed to
any meminfo field.
Add NR_DEFERRED_SPLIT_PAGES to track the total memory consumed by
folios currently on the deferred_split_lru, updated via
mod_node_page_state() at all enqueue/dequeue points. The new field
DeferredSplitPages is visible in /proc/meminfo, /proc/vmstat, and
per-node /sys/devices/system/node/node*/meminfo.
Signed-off-by: Ye Liu <liuye@kylinos.cn>
---
drivers/base/node.c | 4 +++-
fs/proc/meminfo.c | 2 ++
include/linux/mmzone.h | 1 +
mm/huge_memory.c | 24 +++++++++++++++++++++---
mm/vmstat.c | 1 +
5 files changed, 28 insertions(+), 4 deletions(-)
diff --git a/drivers/base/node.c b/drivers/base/node.c
index 3da91929ad4e..69463438300e 100644
--- a/drivers/base/node.c
+++ b/drivers/base/node.c
@@ -519,6 +519,7 @@ static ssize_t node_read_meminfo(struct device *dev,
"Node %d ShmemPmdMapped: %8lu kB\n"
"Node %d FileHugePages: %8lu kB\n"
"Node %d FilePmdMapped: %8lu kB\n"
+ "Node %d DeferredSplitPages: %8lu kB\n"
#endif
#ifdef CONFIG_UNACCEPTED_MEMORY
"Node %d Unaccepted: %8lu kB\n"
@@ -553,7 +554,8 @@ static ssize_t node_read_meminfo(struct device *dev,
nid, K(node_page_state(pgdat, NR_SHMEM_THPS)),
nid, K(node_page_state(pgdat, NR_SHMEM_PMDMAPPED)),
nid, K(node_page_state(pgdat, NR_FILE_THPS)),
- nid, K(node_page_state(pgdat, NR_FILE_PMDMAPPED))
+ nid, K(node_page_state(pgdat, NR_FILE_PMDMAPPED)),
+ nid, K(node_page_state(pgdat, NR_DEFERRED_SPLIT_PAGES))
#endif
#ifdef CONFIG_UNACCEPTED_MEMORY
,
diff --git a/fs/proc/meminfo.c b/fs/proc/meminfo.c
index b2813ff13cb2..76dbf51ad1e0 100644
--- a/fs/proc/meminfo.c
+++ b/fs/proc/meminfo.c
@@ -149,6 +149,8 @@ static int meminfo_proc_show(struct seq_file *m, void *v)
global_node_page_state(NR_FILE_THPS));
show_val_kb(m, "FilePmdMapped: ",
global_node_page_state(NR_FILE_PMDMAPPED));
+ show_val_kb(m, "DeferredSplitPages: ",
+ global_node_page_state(NR_DEFERRED_SPLIT_PAGES));
#endif
#ifdef CONFIG_CMA
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 0507193b3ae3..1e75adb73d00 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -267,6 +267,7 @@ enum node_stat_item {
NR_FILE_THPS,
NR_FILE_PMDMAPPED,
NR_ANON_THPS,
+ NR_DEFERRED_SPLIT_PAGES, /* THP/mTHP pages pending deferred split */
NR_VMSCAN_WRITE,
NR_VMSCAN_IMMEDIATE, /* Prioritise for reclaim when writeback ends */
NR_DIRTIED, /* page dirtyings since bootup */
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index c642bec967fa..1094b844675c 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -77,6 +77,14 @@ static unsigned long deferred_split_scan(struct shrinker *shrink,
struct shrink_control *sc);
static bool split_underused_thp = true;
+#define deferred_split_pages_add(folio) \
+ mod_node_page_state(NODE_DATA(folio_nid(folio)), \
+ NR_DEFERRED_SPLIT_PAGES, folio_nr_pages(folio))
+
+#define deferred_split_pages_del(folio) \
+ mod_node_page_state(NODE_DATA(folio_nid(folio)), \
+ NR_DEFERRED_SPLIT_PAGES, -folio_nr_pages(folio))
+
static atomic_t huge_zero_refcount;
struct folio *huge_zero_folio __read_mostly;
unsigned long huge_zero_pfn __read_mostly = ~0UL;
@@ -3913,8 +3921,10 @@ static int __folio_freeze_and_split_unmapped(struct folio *folio, unsigned int n
struct lruvec *lruvec;
if (dequeue_deferred) {
- __list_lru_del(&deferred_split_lru, lru,
- &folio->_deferred_list, folio_nid(folio));
+ if (__list_lru_del(&deferred_split_lru, lru,
+ &folio->_deferred_list, folio_nid(folio)) &&
+ folio_test_partially_mapped(folio))
+ deferred_split_pages_del(folio);
if (folio_test_partially_mapped(folio)) {
folio_clear_partially_mapped(folio);
mod_mthp_stat(old_order,
@@ -4415,6 +4425,7 @@ bool __folio_unqueue_deferred_split(struct folio *folio)
lru = list_lru_lock_irqsave(&deferred_split_lru, nid, &memcg, &flags);
if (__list_lru_del(&deferred_split_lru, lru, &folio->_deferred_list, nid)) {
if (folio_test_partially_mapped(folio)) {
+ deferred_split_pages_del(folio);
folio_clear_partially_mapped(folio);
mod_mthp_stat(folio_order(folio),
MTHP_STAT_NR_ANON_PARTIALLY_MAPPED, -1);
@@ -4473,6 +4484,8 @@ void deferred_split_folio(struct folio *folio, bool partially_mapped)
VM_WARN_ON_FOLIO(folio_test_partially_mapped(folio), folio);
}
__list_lru_add(&deferred_split_lru, lru, &folio->_deferred_list, nid, memcg);
+ if (partially_mapped)
+ deferred_split_pages_add(folio);
list_lru_unlock_irqrestore(lru, &flags);
rcu_read_unlock();
}
@@ -4524,8 +4537,11 @@ static enum lru_status deferred_split_isolate(struct list_head *item,
{
struct folio *folio = container_of(item, struct folio, _deferred_list);
struct list_head *freeable = cb_arg;
+ bool partially_mapped = folio_test_partially_mapped(folio);
if (folio_try_get(folio)) {
+ if (partially_mapped)
+ deferred_split_pages_del(folio);
list_lru_isolate_move(lru, item, freeable);
return LRU_REMOVED;
}
@@ -4535,7 +4551,8 @@ static enum lru_status deferred_split_isolate(struct list_head *item,
* isolate: folio_unqueue_deferred_split() checks list_empty()
* locklessly, so once removed the folio can be freed any time.
*/
- if (folio_test_partially_mapped(folio)) {
+ if (partially_mapped) {
+ deferred_split_pages_del(folio);
folio_clear_partially_mapped(folio);
mod_mthp_stat(folio_order(folio),
MTHP_STAT_NR_ANON_PARTIALLY_MAPPED, -1);
@@ -4596,6 +4613,7 @@ static unsigned long deferred_split_scan(struct shrinker *shrink,
&folio->_deferred_list,
folio_nid(folio),
folio_memcg(folio));
+ deferred_split_pages_add(folio);
rcu_read_unlock();
}
folio_put(folio);
diff --git a/mm/vmstat.c b/mm/vmstat.c
index 3b5cb1031f72..ba71cc3e4c30 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1248,6 +1248,7 @@ const char * const vmstat_text[] = {
[I(NR_FILE_THPS)] = "nr_file_hugepages",
[I(NR_FILE_PMDMAPPED)] = "nr_file_pmdmapped",
[I(NR_ANON_THPS)] = "nr_anon_transparent_hugepages",
+ [I(NR_DEFERRED_SPLIT_PAGES)] = "nr_deferred_split_pages",
[I(NR_VMSCAN_WRITE)] = "nr_vmscan_write",
[I(NR_VMSCAN_IMMEDIATE)] = "nr_vmscan_immediate_reclaim",
[I(NR_DIRTIED)] = "nr_dirtied",
--
2.43.0
next reply other threads:[~2026-07-17 6:31 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-07-17 6:30 Ye Liu [this message]
2026-07-17 8:08 ` [PATCH] mm/thp: expose deferred split folio memory usage in meminfo Lorenzo Stoakes (ARM)
2026-07-17 9:24 ` Ye Liu
2026-07-17 9:38 ` liuye
2026-07-17 9:47 ` Lorenzo Stoakes (ARM)
2026-07-17 10:29 ` Johannes Weiner
2026-07-17 8:37 ` David Hildenbrand (Arm)
2026-07-17 8:47 ` Lorenzo Stoakes (ARM)
2026-07-17 9:31 ` Ye Liu
2026-07-17 9:33 ` David Hildenbrand (Arm)
2026-07-17 9:48 ` Lorenzo Stoakes (ARM)
2026-07-17 9:54 ` Ye Liu
2026-07-17 10:29 ` David Hildenbrand (Arm)
2026-07-17 10:29 ` Vlastimil Babka (SUSE)
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