[RFC PATCH v2 0/2] mm: multi-gen LRU scanning for page promotion

[RFC PATCH v2 0/2] mm: multi-gen LRU scanning for page promotion

[Kinsey Ho]

This patch series introduces a software-based approach to identifying
hot pages for promotion in tiered memory systems, particularly those
leveraging CXL-attached memory, by utilizing the Multi-Generational
LRU (MGLRU) framework. This method is designed to complement
hardware-based hotness detection mechanisms like Intel PMU sampling, AMD
IBS, or dedicated CXL memory monitoring units, providing a more
comprehensive view of page access patterns, similar to kmmscand [1].

We propose to utilize MGLRU's existing infrastructure to provide hot
page information. A key benefit here is the reuse of the MGLRU page
table walk code, thus avoiding the overhead and duplication of effort
involved in implementing a separate page table scanning mechanism. The
working set reporting proposal [2] also reuses MGLRU's infrastructure,
but focuses on cold page detection. It provides its own aging daemon,
which could additionally provide hot page information by integrating
this proof-of-concept.

This series is based on and relies on [3] as the aggregation and
promotion engine to implement the promotion policies. This is still in
the RFC stage as a proof-of-concept and requires more rigorous testing.

---
v2: Fixed a correctness issue during page table walk, where, on resume,
one page found with the access-bit set was incorrectly not added to the
pghot data structure provided by [3].

v1: https://lore.kernel.org/linux-mm/20250324220301.1273038-1-kinseyho@google.com/
---

[1] [RFC PATCH V3 00/17] mm: slowtier page promotion based on PTE A bit
https://lore.kernel.org/linux-mm/20250814153307.1553061-1-raghavendra.kt@amd.com/

[2] [PATCH v4 0/9] mm: workingset reporting
https://lore.kernel.org/linux-mm/20241127025728.3689245-1-yuanchu@google.com/

[3] [RFC PATCH v2 0/8] mm: Hot page tracking and promotion infrastructure
https://lore.kernel.org/linux-mm/20250910144653.212066-1-bharata@amd.com/

Kinsey Ho (2):
  mm: mglru: generalize page table walk
  mm: klruscand: use mglru scanning for page promotion

 include/linux/mmzone.h |   5 ++
 mm/Kconfig             |   8 ++
 mm/Makefile            |   1 +
 mm/internal.h          |   4 +
 mm/klruscand.c         | 118 +++++++++++++++++++++++++++
 mm/vmscan.c            | 181 +++++++++++++++++++++++++++++++----------
 6 files changed, 272 insertions(+), 45 deletions(-)
 create mode 100644 mm/klruscand.c

-- 
2.51.0.384.g4c02a37b29-goog

[RFC PATCH v2 1/2] mm: mglru: generalize page table walk

[Kinsey Ho]

Refactor the existing MGLRU page table walking logic to make it
resumable.

Additionally, introduce two hooks into the MGLRU page table walk:
accessed callback and flush callback. The accessed callback is called
for each accessed page detected via the scanned accessed bit. The flush
callback is called when the accessed callback reports that a flush is
required. This allows for processing pages in batches for efficiency.

With a generalised page table walk, introduce a new scan function which
repeatedly scans on the same young generation and does not add a new
young generation.

Signed-off-by: Kinsey Ho <kinseyho@google.com>
Signed-off-by: Yuanchu Xie <yuanchu@google.com>
---
 include/linux/mmzone.h |   5 ++
 mm/internal.h          |   4 +
 mm/vmscan.c            | 181 +++++++++++++++++++++++++++++++----------
 3 files changed, 145 insertions(+), 45 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index f7094babed10..a30fbdbb1a57 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -533,6 +533,8 @@ struct lru_gen_mm_walk {
 	unsigned long seq;
 	/* the next address within an mm to scan */
 	unsigned long next_addr;
+	/* called for each accessed pte/pmd */
+	bool (*accessed_cb)(unsigned long pfn);
 	/* to batch promoted pages */
 	int nr_pages[MAX_NR_GENS][ANON_AND_FILE][MAX_NR_ZONES];
 	/* to batch the mm stats */
@@ -540,6 +542,9 @@ struct lru_gen_mm_walk {
 	/* total batched items */
 	int batched;
 	int swappiness;
+	/* for the pmd under scanning */
+	int nr_young_pte;
+	int nr_total_pte;
 	bool force_scan;
 };
 
diff --git a/mm/internal.h b/mm/internal.h
index 45b725c3dc03..f8ca128f61ab 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -538,6 +538,10 @@ extern unsigned long highest_memmap_pfn;
 bool folio_isolate_lru(struct folio *folio);
 void folio_putback_lru(struct folio *folio);
 extern void reclaim_throttle(pg_data_t *pgdat, enum vmscan_throttle_state reason);
+void set_task_reclaim_state(struct task_struct *task,
+				   struct reclaim_state *rs);
+void lru_gen_scan_lruvec(struct lruvec *lruvec, unsigned long seq,
+			 bool (*accessed_cb)(unsigned long), void (*flush_cb)(void));
 #ifdef CONFIG_NUMA
 int user_proactive_reclaim(char *buf,
 			   struct mem_cgroup *memcg, pg_data_t *pgdat);
diff --git a/mm/vmscan.c b/mm/vmscan.c
index a48aec8bfd92..88db10f1aee2 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -289,7 +289,7 @@ static int sc_swappiness(struct scan_control *sc, struct mem_cgroup *memcg)
 			continue;				\
 		else
 
-static void set_task_reclaim_state(struct task_struct *task,
+void set_task_reclaim_state(struct task_struct *task,
 				   struct reclaim_state *rs)
 {
 	/* Check for an overwrite */
@@ -3092,7 +3092,7 @@ static bool iterate_mm_list(struct lru_gen_mm_walk *walk, struct mm_struct **ite
 
 	VM_WARN_ON_ONCE(mm_state->seq + 1 < walk->seq);
 
-	if (walk->seq <= mm_state->seq)
+	if (!walk->accessed_cb && walk->seq <= mm_state->seq)
 		goto done;
 
 	if (!mm_state->head)
@@ -3518,16 +3518,14 @@ static void walk_update_folio(struct lru_gen_mm_walk *walk, struct folio *folio,
 	}
 }
 
-static bool walk_pte_range(pmd_t *pmd, unsigned long start, unsigned long end,
-			   struct mm_walk *args)
+static int walk_pte_range(pmd_t *pmd, unsigned long start, unsigned long end,
+			   struct mm_walk *args, bool *suitable)
 {
 	int i;
 	bool dirty;
 	pte_t *pte;
 	spinlock_t *ptl;
 	unsigned long addr;
-	int total = 0;
-	int young = 0;
 	struct folio *last = NULL;
 	struct lru_gen_mm_walk *walk = args->private;
 	struct mem_cgroup *memcg = lruvec_memcg(walk->lruvec);
@@ -3535,19 +3533,24 @@ static bool walk_pte_range(pmd_t *pmd, unsigned long start, unsigned long end,
 	DEFINE_MAX_SEQ(walk->lruvec);
 	int gen = lru_gen_from_seq(max_seq);
 	pmd_t pmdval;
+	int err = 0;
 
 	pte = pte_offset_map_rw_nolock(args->mm, pmd, start & PMD_MASK, &pmdval, &ptl);
-	if (!pte)
-		return false;
+	if (!pte) {
+		*suitable = false;
+		return err;
+	}
 
 	if (!spin_trylock(ptl)) {
 		pte_unmap(pte);
-		return true;
+		*suitable = true;
+		return err;
 	}
 
 	if (unlikely(!pmd_same(pmdval, pmdp_get_lockless(pmd)))) {
 		pte_unmap_unlock(pte, ptl);
-		return false;
+		*suitable = false;
+		return err;
 	}
 
 	arch_enter_lazy_mmu_mode();
@@ -3556,8 +3559,9 @@ static bool walk_pte_range(pmd_t *pmd, unsigned long start, unsigned long end,
 		unsigned long pfn;
 		struct folio *folio;
 		pte_t ptent = ptep_get(pte + i);
+		bool do_flush;
 
-		total++;
+		walk->nr_total_pte++;
 		walk->mm_stats[MM_LEAF_TOTAL]++;
 
 		pfn = get_pte_pfn(ptent, args->vma, addr, pgdat);
@@ -3581,23 +3585,36 @@ static bool walk_pte_range(pmd_t *pmd, unsigned long start, unsigned long end,
 		if (pte_dirty(ptent))
 			dirty = true;
 
-		young++;
+		walk->nr_young_pte++;
 		walk->mm_stats[MM_LEAF_YOUNG]++;
+
+		if (!walk->accessed_cb)
+			continue;
+
+		do_flush = walk->accessed_cb(pfn);
+		if (do_flush) {
+			walk->next_addr = addr + PAGE_SIZE;
+
+			err = -EAGAIN;
+			break;
+		}
 	}
 
 	walk_update_folio(walk, last, gen, dirty);
 	last = NULL;
 
-	if (i < PTRS_PER_PTE && get_next_vma(PMD_MASK, PAGE_SIZE, args, &start, &end))
+	if (!err && i < PTRS_PER_PTE &&
+	    get_next_vma(PMD_MASK, PAGE_SIZE, args, &start, &end))
 		goto restart;
 
 	arch_leave_lazy_mmu_mode();
 	pte_unmap_unlock(pte, ptl);
 
-	return suitable_to_scan(total, young);
+	*suitable = suitable_to_scan(walk->nr_total_pte, walk->nr_young_pte);
+	return err;
 }
 
-static void walk_pmd_range_locked(pud_t *pud, unsigned long addr, struct vm_area_struct *vma,
+static int walk_pmd_range_locked(pud_t *pud, unsigned long addr, struct vm_area_struct *vma,
 				  struct mm_walk *args, unsigned long *bitmap, unsigned long *first)
 {
 	int i;
@@ -3610,6 +3627,7 @@ static void walk_pmd_range_locked(pud_t *pud, unsigned long addr, struct vm_area
 	struct pglist_data *pgdat = lruvec_pgdat(walk->lruvec);
 	DEFINE_MAX_SEQ(walk->lruvec);
 	int gen = lru_gen_from_seq(max_seq);
+	int err = 0;
 
 	VM_WARN_ON_ONCE(pud_leaf(*pud));
 
@@ -3617,13 +3635,13 @@ static void walk_pmd_range_locked(pud_t *pud, unsigned long addr, struct vm_area
 	if (*first == -1) {
 		*first = addr;
 		bitmap_zero(bitmap, MIN_LRU_BATCH);
-		return;
+		return err;
 	}
 
 	i = addr == -1 ? 0 : pmd_index(addr) - pmd_index(*first);
 	if (i && i <= MIN_LRU_BATCH) {
 		__set_bit(i - 1, bitmap);
-		return;
+		return err;
 	}
 
 	pmd = pmd_offset(pud, *first);
@@ -3637,6 +3655,7 @@ static void walk_pmd_range_locked(pud_t *pud, unsigned long addr, struct vm_area
 	do {
 		unsigned long pfn;
 		struct folio *folio;
+		bool do_flush;
 
 		/* don't round down the first address */
 		addr = i ? (*first & PMD_MASK) + i * PMD_SIZE : *first;
@@ -3673,6 +3692,17 @@ static void walk_pmd_range_locked(pud_t *pud, unsigned long addr, struct vm_area
 			dirty = true;
 
 		walk->mm_stats[MM_LEAF_YOUNG]++;
+		if (!walk->accessed_cb)
+			goto next;
+
+		do_flush = walk->accessed_cb(pfn);
+		if (do_flush) {
+			i = find_next_bit(bitmap, MIN_LRU_BATCH, i) + 1;
+
+			walk->next_addr = (*first & PMD_MASK) + i * PMD_SIZE;
+			err = -EAGAIN;
+			break;
+		}
 next:
 		i = i > MIN_LRU_BATCH ? 0 : find_next_bit(bitmap, MIN_LRU_BATCH, i) + 1;
 	} while (i <= MIN_LRU_BATCH);
@@ -3683,9 +3713,10 @@ static void walk_pmd_range_locked(pud_t *pud, unsigned long addr, struct vm_area
 	spin_unlock(ptl);
 done:
 	*first = -1;
+	return err;
 }
 
-static void walk_pmd_range(pud_t *pud, unsigned long start, unsigned long end,
+static int walk_pmd_range(pud_t *pud, unsigned long start, unsigned long end,
 			   struct mm_walk *args)
 {
 	int i;
@@ -3697,6 +3728,7 @@ static void walk_pmd_range(pud_t *pud, unsigned long start, unsigned long end,
 	unsigned long first = -1;
 	struct lru_gen_mm_walk *walk = args->private;
 	struct lru_gen_mm_state *mm_state = get_mm_state(walk->lruvec);
+	int err = 0;
 
 	VM_WARN_ON_ONCE(pud_leaf(*pud));
 
@@ -3710,6 +3742,7 @@ static void walk_pmd_range(pud_t *pud, unsigned long start, unsigned long end,
 	/* walk_pte_range() may call get_next_vma() */
 	vma = args->vma;
 	for (i = pmd_index(start), addr = start; addr != end; i++, addr = next) {
+		bool suitable;
 		pmd_t val = pmdp_get_lockless(pmd + i);
 
 		next = pmd_addr_end(addr, end);
@@ -3726,7 +3759,10 @@ static void walk_pmd_range(pud_t *pud, unsigned long start, unsigned long end,
 			walk->mm_stats[MM_LEAF_TOTAL]++;
 
 			if (pfn != -1)
-				walk_pmd_range_locked(pud, addr, vma, args, bitmap, &first);
+				err = walk_pmd_range_locked(pud, addr, vma, args,
+						bitmap, &first);
+			if (err)
+				return err;
 			continue;
 		}
 
@@ -3735,33 +3771,51 @@ static void walk_pmd_range(pud_t *pud, unsigned long start, unsigned long end,
 			if (!pmd_young(val))
 				continue;
 
-			walk_pmd_range_locked(pud, addr, vma, args, bitmap, &first);
+			err = walk_pmd_range_locked(pud, addr, vma, args,
+						bitmap, &first);
+			if (err)
+				return err;
 		}
 
 		if (!walk->force_scan && !test_bloom_filter(mm_state, walk->seq, pmd + i))
 			continue;
 
+		err = walk_pte_range(&val, addr, next, args, &suitable);
+		if (err && walk->next_addr < next && first == -1)
+			return err;
+
+		walk->nr_total_pte = 0;
+		walk->nr_young_pte = 0;
+
 		walk->mm_stats[MM_NONLEAF_FOUND]++;
 
-		if (!walk_pte_range(&val, addr, next, args))
-			continue;
+		if (!suitable)
+			goto next;
 
 		walk->mm_stats[MM_NONLEAF_ADDED]++;
 
 		/* carry over to the next generation */
 		update_bloom_filter(mm_state, walk->seq + 1, pmd + i);
+next:
+		if (err) {
+			walk->next_addr = first;
+			return err;
+		}
 	}
 
-	walk_pmd_range_locked(pud, -1, vma, args, bitmap, &first);
+	err = walk_pmd_range_locked(pud, -1, vma, args, bitmap, &first);
 
-	if (i < PTRS_PER_PMD && get_next_vma(PUD_MASK, PMD_SIZE, args, &start, &end))
+	if (!err && i < PTRS_PER_PMD &&
+	    get_next_vma(PUD_MASK, PMD_SIZE, args, &start, &end))
 		goto restart;
+
+	return err;
 }
 
 static int walk_pud_range(p4d_t *p4d, unsigned long start, unsigned long end,
 			  struct mm_walk *args)
 {
-	int i;
+	int i, err;
 	pud_t *pud;
 	unsigned long addr;
 	unsigned long next;
@@ -3779,7 +3833,9 @@ static int walk_pud_range(p4d_t *p4d, unsigned long start, unsigned long end,
 		if (!pud_present(val) || WARN_ON_ONCE(pud_leaf(val)))
 			continue;
 
-		walk_pmd_range(&val, addr, next, args);
+		err = walk_pmd_range(&val, addr, next, args);
+		if (err)
+			return err;
 
 		if (need_resched() || walk->batched >= MAX_LRU_BATCH) {
 			end = (addr | ~PUD_MASK) + 1;
@@ -3800,40 +3856,48 @@ static int walk_pud_range(p4d_t *p4d, unsigned long start, unsigned long end,
 	return -EAGAIN;
 }
 
-static void walk_mm(struct mm_struct *mm, struct lru_gen_mm_walk *walk)
+static int try_walk_mm(struct mm_struct *mm, struct lru_gen_mm_walk *walk)
 {
+	int err;
 	static const struct mm_walk_ops mm_walk_ops = {
 		.test_walk = should_skip_vma,
 		.p4d_entry = walk_pud_range,
 		.walk_lock = PGWALK_RDLOCK,
 	};
-	int err;
 	struct lruvec *lruvec = walk->lruvec;
 
-	walk->next_addr = FIRST_USER_ADDRESS;
+	DEFINE_MAX_SEQ(lruvec);
 
-	do {
-		DEFINE_MAX_SEQ(lruvec);
+	err = -EBUSY;
 
-		err = -EBUSY;
+	/* another thread might have called inc_max_seq() */
+	if (walk->seq != max_seq)
+		return err;
 
-		/* another thread might have called inc_max_seq() */
-		if (walk->seq != max_seq)
-			break;
+	/* the caller might be holding the lock for write */
+	if (mmap_read_trylock(mm)) {
+		err = walk_page_range(mm, walk->next_addr, ULONG_MAX,
+				      &mm_walk_ops, walk);
 
-		/* the caller might be holding the lock for write */
-		if (mmap_read_trylock(mm)) {
-			err = walk_page_range(mm, walk->next_addr, ULONG_MAX, &mm_walk_ops, walk);
+		mmap_read_unlock(mm);
+	}
 
-			mmap_read_unlock(mm);
-		}
+	if (walk->batched) {
+		spin_lock_irq(&lruvec->lru_lock);
+		reset_batch_size(walk);
+		spin_unlock_irq(&lruvec->lru_lock);
+	}
 
-		if (walk->batched) {
-			spin_lock_irq(&lruvec->lru_lock);
-			reset_batch_size(walk);
-			spin_unlock_irq(&lruvec->lru_lock);
-		}
+	return err;
+}
+
+static void walk_mm(struct mm_struct *mm, struct lru_gen_mm_walk *walk)
+{
+	int err;
 
+	walk->next_addr = FIRST_USER_ADDRESS;
+	do {
+		err = try_walk_mm(mm, walk);
 		cond_resched();
 	} while (err == -EAGAIN);
 }
@@ -4045,6 +4109,33 @@ static bool inc_max_seq(struct lruvec *lruvec, unsigned long seq, int swappiness
 	return success;
 }
 
+void lru_gen_scan_lruvec(struct lruvec *lruvec, unsigned long seq,
+			 bool (*accessed_cb)(unsigned long), void (*flush_cb)(void))
+{
+	struct lru_gen_mm_walk *walk = current->reclaim_state->mm_walk;
+	struct mm_struct *mm = NULL;
+
+	walk->lruvec = lruvec;
+	walk->seq = seq;
+	walk->accessed_cb = accessed_cb;
+	walk->swappiness = MAX_SWAPPINESS;
+
+	do {
+		int err = -EBUSY;
+
+		iterate_mm_list(walk, &mm);
+		if (!mm)
+			break;
+
+		walk->next_addr = FIRST_USER_ADDRESS;
+		do {
+			err = try_walk_mm(mm, walk);
+			cond_resched();
+			flush_cb();
+		} while (err == -EAGAIN);
+	} while (mm);
+}
+
 static bool try_to_inc_max_seq(struct lruvec *lruvec, unsigned long seq,
 			       int swappiness, bool force_scan)
 {
-- 
2.51.0.384.g4c02a37b29-goog

[RFC PATCH v2 2/2] mm: klruscand: use mglru scanning for page promotion

[Kinsey Ho]

Introduce a new kernel daemon, klruscand, that periodically invokes the
MGLRU page table walk. It leverages the new callbacks to gather access
information and forwards it to the kpromoted daemon for promotion
decisions.

This benefits from reusing the existing MGLRU page table walk
infrastructure, which is optimized with features such as hierarchical
scanning and bloom filters to reduce CPU overhead.

As an additional optimization to be added in the future, we can tune
the scan intervals for each memcg.

Signed-off-by: Kinsey Ho <kinseyho@google.com>
Signed-off-by: Yuanchu Xie <yuanchu@google.com>
---
 mm/Kconfig     |   8 ++++
 mm/Makefile    |   1 +
 mm/klruscand.c | 118 +++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 127 insertions(+)
 create mode 100644 mm/klruscand.c

diff --git a/mm/Kconfig b/mm/Kconfig
index 8b236eb874cf..6d53c1208729 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -1393,6 +1393,14 @@ config PGHOT
 	  by various sources. Asynchronous promotion is done by per-node
 	  kernel threads.
 
+config KLRUSCAND
+	bool "Kernel lower tier access scan daemon"
+	default y
+	depends on PGHOT && LRU_GEN_WALKS_MMU
+	help
+	  Scan for accesses from lower tiers by invoking MGLRU to perform
+	  page table walks.
+
 source "mm/damon/Kconfig"
 
 endmenu
diff --git a/mm/Makefile b/mm/Makefile
index ecdd5241bea8..05a96ec35aa3 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -148,3 +148,4 @@ obj-$(CONFIG_EXECMEM) += execmem.o
 obj-$(CONFIG_TMPFS_QUOTA) += shmem_quota.o
 obj-$(CONFIG_PT_RECLAIM) += pt_reclaim.o
 obj-$(CONFIG_PGHOT) += pghot.o
+obj-$(CONFIG_KLRUSCAND) += klruscand.o
diff --git a/mm/klruscand.c b/mm/klruscand.c
new file mode 100644
index 000000000000..1ee2ac906771
--- /dev/null
+++ b/mm/klruscand.c
@@ -0,0 +1,118 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <linux/memcontrol.h>
+#include <linux/kthread.h>
+#include <linux/module.h>
+#include <linux/vmalloc.h>
+#include <linux/random.h>
+#include <linux/migrate.h>
+#include <linux/mm_inline.h>
+#include <linux/slab.h>
+#include <linux/sched/clock.h>
+#include <linux/memory-tiers.h>
+#include <linux/sched/mm.h>
+#include <linux/sched.h>
+#include <linux/pghot.h>
+
+#include "internal.h"
+
+#define KLRUSCAND_INTERVAL 2000
+#define BATCH_SIZE (2 << 16)
+
+static struct task_struct *scan_thread;
+static unsigned long pfn_batch[BATCH_SIZE];
+static int batch_index;
+
+static void flush_cb(void)
+{
+	int i;
+
+	for (i = 0; i < batch_index; i++) {
+		unsigned long pfn = pfn_batch[i];
+
+		pghot_record_access(pfn, NUMA_NO_NODE,
+					PGHOT_PGTABLE_SCAN, jiffies);
+
+		if (i % 16 == 0)
+			cond_resched();
+	}
+	batch_index = 0;
+}
+
+static bool accessed_cb(unsigned long pfn)
+{
+	WARN_ON_ONCE(batch_index == BATCH_SIZE);
+
+	if (batch_index < BATCH_SIZE)
+		pfn_batch[batch_index++] = pfn;
+
+	return batch_index == BATCH_SIZE;
+}
+
+static int klruscand_run(void *unused)
+{
+	struct lru_gen_mm_walk *walk;
+
+	walk = kzalloc(sizeof(*walk),
+		       __GFP_HIGH | __GFP_NOMEMALLOC | __GFP_NOWARN);
+	if (!walk)
+		return -ENOMEM;
+
+	while (!kthread_should_stop()) {
+		unsigned long next_wake_time;
+		long sleep_time;
+		struct mem_cgroup *memcg;
+		int flags;
+		int nid;
+
+		next_wake_time = jiffies + msecs_to_jiffies(KLRUSCAND_INTERVAL);
+
+		for_each_node_state(nid, N_MEMORY) {
+			pg_data_t *pgdat = NODE_DATA(nid);
+			struct reclaim_state rs = { 0 };
+
+			if (node_is_toptier(nid))
+				continue;
+
+			rs.mm_walk = walk;
+			set_task_reclaim_state(current, &rs);
+			flags = memalloc_noreclaim_save();
+
+			memcg = mem_cgroup_iter(NULL, NULL, NULL);
+			do {
+				struct lruvec *lruvec =
+					mem_cgroup_lruvec(memcg, pgdat);
+				unsigned long max_seq =
+					READ_ONCE((lruvec)->lrugen.max_seq);
+
+				lru_gen_scan_lruvec(lruvec, max_seq, accessed_cb, flush_cb);
+				cond_resched();
+			} while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)));
+
+			memalloc_noreclaim_restore(flags);
+			set_task_reclaim_state(current, NULL);
+			memset(walk, 0, sizeof(*walk));
+		}
+
+		sleep_time = next_wake_time - jiffies;
+		if (sleep_time > 0 && sleep_time != MAX_SCHEDULE_TIMEOUT)
+			schedule_timeout_idle(sleep_time);
+	}
+	kfree(walk);
+	return 0;
+}
+
+static int __init klruscand_init(void)
+{
+	struct task_struct *task;
+
+	task = kthread_run(klruscand_run, NULL, "klruscand");
+
+	if (IS_ERR(task)) {
+		pr_err("Failed to create klruscand kthread\n");
+		return PTR_ERR(task);
+	}
+
+	scan_thread = task;
+	return 0;
+}
+module_init(klruscand_init);
-- 
2.51.0.384.g4c02a37b29-goog