omarchy-pkgs/pkgbuilds/linux-omarchy-eevdf/0280-mm-updates.patch

diff --git a/drivers/block/zram/backend_842.c b/drivers/block/zram/backend_842.c
--- a/drivers/block/zram/backend_842.c
+++ b/drivers/block/zram/backend_842.c
@@ -1,5 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0-or-later
 
+#define pr_fmt(fmt) "842: " fmt
+
 #include <linux/kernel.h>
 #include <linux/slab.h>
 #include <linux/sw842.h>
@@ -13,6 +15,14 @@ static void release_params_842(struct zcomp_params *params)
 
 static int setup_params_842(struct zcomp_params *params)
 {
+	if (params->dict_sz) {
+		pr_err("dictionary is not supported\n");
+		return -EOPNOTSUPP;
+	}
+	if (params->level != ZCOMP_PARAM_NOT_SET) {
+		pr_err("compression level is not supported\n");
+		return -EOPNOTSUPP;
+	}
 	return 0;
 }
 
diff --git a/drivers/block/zram/backend_deflate.c b/drivers/block/zram/backend_deflate.c
--- a/drivers/block/zram/backend_deflate.c
+++ b/drivers/block/zram/backend_deflate.c
@@ -1,5 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0-or-later
 
+#define pr_fmt(fmt) "deflate: " fmt
+
 #include <linux/kernel.h>
 #include <linux/slab.h>
 #include <linux/vmalloc.h>
@@ -22,15 +24,26 @@ static void deflate_release_params(struct zcomp_params *params)
 
 static int deflate_setup_params(struct zcomp_params *params)
 {
-	if (params->level == ZCOMP_PARAM_NOT_SET)
+	if (params->dict_sz) {
+		pr_err("dictionary is not supported\n");
+		return -EOPNOTSUPP;
+	}
+
+	if (params->level == ZCOMP_PARAM_NOT_SET) {
 		params->level = Z_DEFAULT_COMPRESSION;
+	} else if (params->level < Z_DEFAULT_COMPRESSION ||
+		   params->level > Z_BEST_COMPRESSION) {
+		pr_err("invalid compression level %d\n", params->level);
+		return -EINVAL;
+	}
+
 	if (params->deflate.winbits == ZCOMP_PARAM_NOT_SET) {
 		params->deflate.winbits = DEFLATE_DEF_WINBITS;
 	} else {
 		s32 wb = params->deflate.winbits;
 
 		if ((wb < -15 || wb > -9) && (wb < 9 || wb > 15)) {
-			pr_err("invalid deflate winbits: %d\n", wb);
+			pr_err("invalid winbits %d\n", wb);
 			return -EINVAL;
 		}
 	}
diff --git a/drivers/block/zram/backend_lz4.c b/drivers/block/zram/backend_lz4.c
--- a/drivers/block/zram/backend_lz4.c
+++ b/drivers/block/zram/backend_lz4.c
@@ -1,3 +1,7 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#define pr_fmt(fmt) "lz4: " fmt
+
 #include <linux/kernel.h>
 #include <linux/lz4.h>
 #include <linux/slab.h>
@@ -28,8 +32,12 @@ static int lz4_setup_params(struct zcomp_params *params)
 	LZ4_stream_t *dict_stream;
 	int ret;
 
-	if (params->level == ZCOMP_PARAM_NOT_SET)
+	if (params->level == ZCOMP_PARAM_NOT_SET) {
 		params->level = LZ4_ACCELERATION_DEFAULT;
+	} else if (params->level < LZ4_ACCELERATION_DEFAULT) {
+		pr_err("invalid compression level %d\n", params->level);
+		return -EINVAL;
+	}
 
 	if (!params->dict || !params->dict_sz)
 		return 0;
diff --git a/drivers/block/zram/backend_lz4hc.c b/drivers/block/zram/backend_lz4hc.c
--- a/drivers/block/zram/backend_lz4hc.c
+++ b/drivers/block/zram/backend_lz4hc.c
@@ -1,3 +1,7 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#define pr_fmt(fmt) "lz4hc: " fmt
+
 #include <linux/kernel.h>
 #include <linux/lz4.h>
 #include <linux/slab.h>
@@ -18,8 +22,18 @@ static void lz4hc_release_params(struct zcomp_params *params)
 
 static int lz4hc_setup_params(struct zcomp_params *params)
 {
-	if (params->level == ZCOMP_PARAM_NOT_SET)
+	if (params->level == ZCOMP_PARAM_NOT_SET) {
 		params->level = LZ4HC_DEFAULT_CLEVEL;
+	} else if (params->level < 1 || params->level > LZ4HC_MAX_CLEVEL) {
+		/*
+		 * Use < 1 rather than < LZ4HC_MIN_CLEVEL here because
+		 * LZ4HC_compress_generic() only clamps levels below 1
+		 * (levels 1 and 2 are valid). LZ4HC_MIN_CLEVEL (3) is
+		 * advisory and not enforced by the library.
+		 */
+		pr_err("invalid compression level %d\n", params->level);
+		return -EINVAL;
+	}
 
 	return 0;
 }
diff --git a/drivers/block/zram/backend_lzo.c b/drivers/block/zram/backend_lzo.c
--- a/drivers/block/zram/backend_lzo.c
+++ b/drivers/block/zram/backend_lzo.c
@@ -1,5 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0-or-later
 
+#define pr_fmt(fmt) "lzo: " fmt
+
 #include <linux/kernel.h>
 #include <linux/slab.h>
 #include <linux/lzo.h>
@@ -12,6 +14,14 @@ static void lzo_release_params(struct zcomp_params *params)
 
 static int lzo_setup_params(struct zcomp_params *params)
 {
+	if (params->dict_sz) {
+		pr_err("dictionary is not supported\n");
+		return -EOPNOTSUPP;
+	}
+	if (params->level != ZCOMP_PARAM_NOT_SET) {
+		pr_err("compression level is not supported\n");
+		return -EOPNOTSUPP;
+	}
 	return 0;
 }
 
diff --git a/drivers/block/zram/backend_lzorle.c b/drivers/block/zram/backend_lzorle.c
--- a/drivers/block/zram/backend_lzorle.c
+++ b/drivers/block/zram/backend_lzorle.c
@@ -1,5 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0-or-later
 
+#define pr_fmt(fmt) "lzo-rle: " fmt
+
 #include <linux/kernel.h>
 #include <linux/slab.h>
 #include <linux/lzo.h>
@@ -12,6 +14,14 @@ static void lzorle_release_params(struct zcomp_params *params)
 
 static int lzorle_setup_params(struct zcomp_params *params)
 {
+	if (params->dict_sz) {
+		pr_err("dictionary is not supported\n");
+		return -EOPNOTSUPP;
+	}
+	if (params->level != ZCOMP_PARAM_NOT_SET) {
+		pr_err("compression level is not supported\n");
+		return -EOPNOTSUPP;
+	}
 	return 0;
 }
 
diff --git a/drivers/block/zram/backend_zstd.c b/drivers/block/zram/backend_zstd.c
--- a/drivers/block/zram/backend_zstd.c
+++ b/drivers/block/zram/backend_zstd.c
@@ -1,5 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0-or-later
 
+#define pr_fmt(fmt) "zstd: " fmt
+
 #include <linux/kernel.h>
 #include <linux/slab.h>
 #include <linux/vmalloc.h>
@@ -58,8 +60,13 @@ static int zstd_setup_params(struct zcomp_params *params)
 		return -ENOMEM;
 
 	params->drv_data = zp;
-	if (params->level == ZCOMP_PARAM_NOT_SET)
+	if (params->level == ZCOMP_PARAM_NOT_SET) {
 		params->level = zstd_default_clevel();
+	} else if (params->level < zstd_min_clevel() ||
+		   params->level > zstd_max_clevel()) {
+		pr_err("invalid compression level %d\n", params->level);
+		goto error;
+	}
 
 	zp->cprm = zstd_get_params(params->level, PAGE_SIZE);
 
@@ -85,7 +92,6 @@ static int zstd_setup_params(struct zcomp_params *params)
 	return 0;
 
 error:
-	zstd_release_params(params);
 	return -EINVAL;
 }
 
@@ -161,7 +167,6 @@ static int zstd_create(struct zcomp_params *params, struct zcomp_ctx *ctx)
 	return 0;
 
 error:
-	zstd_release_params(params);
 	zstd_destroy(ctx);
 	return -EINVAL;
 }
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -1664,6 +1664,17 @@ static void comp_algorithm_set(struct zram *zram, u32 prio, const char *alg)
 	zram->comp_algs[prio] = alg;
 }
 
+static void comp_params_reset(struct zram *zram, u32 prio)
+{
+	struct zcomp_params *params = &zram->params[prio];
+
+	vfree(params->dict);
+	params->level = ZCOMP_PARAM_NOT_SET;
+	params->deflate.winbits = ZCOMP_PARAM_NOT_SET;
+	params->dict_sz = 0;
+	params->dict = NULL;
+}
+
 static int __comp_algorithm_store(struct zram *zram, u32 prio, const char *buf)
 {
 	const char *alg;
@@ -1684,20 +1695,10 @@ static int __comp_algorithm_store(struct zram *zram, u32 prio, const char *buf)
 	}
 
 	comp_algorithm_set(zram, prio, alg);
+	comp_params_reset(zram, prio);
 	return 0;
 }
 
-static void comp_params_reset(struct zram *zram, u32 prio)
-{
-	struct zcomp_params *params = &zram->params[prio];
-
-	vfree(params->dict);
-	params->level = ZCOMP_PARAM_NOT_SET;
-	params->deflate.winbits = ZCOMP_PARAM_NOT_SET;
-	params->dict_sz = 0;
-	params->dict = NULL;
-}
-
 static int comp_params_store(struct zram *zram, u32 prio, s32 level,
 			     const char *dict_path,
 			     struct deflate_params *deflate_params)
@@ -1712,8 +1713,16 @@ static int comp_params_store(struct zram *zram, u32 prio, s32 level,
 						INT_MAX,
 						NULL,
 						READING_POLICY);
-		if (sz < 0)
+		if (sz < 0) {
+			pr_err("failed to load dictionary %s (err=%zd)\n",
+			       dict_path, sz);
+			return sz;
+		}
+		if (sz == 0) {
+			pr_err("failed to load dictionary %s (empty file)\n",
+			       dict_path);
 			return -EINVAL;
+		}
 	}
 
 	zram->params[prio].dict_sz = sz;
diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -952,6 +952,8 @@ unsigned long memcg_page_state_output(struct mem_cgroup *memcg, int item);
 bool memcg_stat_item_valid(int idx);
 bool memcg_vm_event_item_valid(enum vm_event_item idx);
 unsigned long lruvec_page_state(struct lruvec *lruvec, enum node_stat_item idx);
+unsigned long lruvec_page_state_monotonic(struct lruvec *lruvec,
+					  enum node_stat_item idx);
 unsigned long lruvec_page_state_local(struct lruvec *lruvec,
 				      enum node_stat_item idx);
 
@@ -1404,6 +1406,12 @@ static inline unsigned long lruvec_page_state(struct lruvec *lruvec,
 	return node_page_state(lruvec_pgdat(lruvec), idx);
 }
 
+static inline unsigned long lruvec_page_state_monotonic(struct lruvec *lruvec,
+							enum node_stat_item idx)
+{
+	return node_page_state_monotonic(lruvec_pgdat(lruvec), idx);
+}
+
 static inline unsigned long lruvec_page_state_local(struct lruvec *lruvec,
 						    enum node_stat_item idx)
 {
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -323,6 +323,8 @@ enum node_stat_item {
 	PGSCAN_PROACTIVE,
 	PGSCAN_ANON,
 	PGSCAN_FILE,
+	PGROTATE_ANON,
+	PGROTATE_FILE,
 	PGREFILL,
 #ifdef CONFIG_HUGETLB_PAGE
 	NR_HUGETLB,
@@ -755,6 +757,12 @@ void lru_gen_reparent_memcg(struct mem_cgroup *memcg, struct mem_cgroup *parent,
 
 #endif /* CONFIG_LRU_GEN */
 
+struct lru_cost {
+	unsigned long		count;
+	unsigned long		last_rotated;
+	unsigned long		last_io;
+};
+
 struct lruvec {
 	struct list_head		lists[NR_LRU_LISTS];
 	/* per lruvec lru_lock for memcg */
@@ -763,9 +771,12 @@ struct lruvec {
 	 * These track the cost of reclaiming one LRU - file or anon -
 	 * over the other. As the observed cost of reclaiming one LRU
 	 * increases, the reclaim scan balance tips toward the other.
+	 * Updated and decayed at prepare_scan_control() time; cost_lock
+	 * serialises that update.
 	 */
-	unsigned long			anon_cost;
-	unsigned long			file_cost;
+	struct lru_cost			cost[ANON_AND_FILE];
+	/* Protects cost[]. */
+	spinlock_t			cost_lock;
 	/* Non-resident age, driven by LRU movement */
 	atomic_long_t			nonresident_age;
 	/* Refaults at the time of last reclaim cycle */
diff --git a/include/linux/swap.h b/include/linux/swap.h
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -309,9 +309,6 @@ extern unsigned long totalreserve_pages;
 
 
 /* linux/mm/swap.c */
-void lru_note_cost_unlock_irq(struct lruvec *lruvec, bool file,
-		unsigned int nr_io, unsigned int nr_rotated);
-void lru_note_cost_refault(struct folio *);
 void folio_add_lru(struct folio *);
 void folio_add_lru_vma(struct folio *, struct vm_area_struct *);
 void mark_page_accessed(struct page *);
diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h
--- a/include/linux/vmstat.h
+++ b/include/linux/vmstat.h
@@ -20,7 +20,6 @@ struct reclaim_stat {
 	unsigned nr_congested;
 	unsigned nr_writeback;
 	unsigned nr_immediate;
-	unsigned nr_pageout;
 	unsigned nr_activate[ANON_AND_FILE];
 	unsigned nr_ref_keep;
 	unsigned nr_unmap_fail;
@@ -194,6 +193,19 @@ unsigned long global_node_page_state_pages(enum node_stat_item item)
 	return x;
 }
 
+/*
+ * Non-clamping variant of global_node_page_state() intended for callers that
+ * snapshot a monotonically-incremented counter and subtract two samples.
+ * Returns the raw wrapping value so that unsigned modular subtraction stays
+ * correct across a signed-long overflow (a real hazard on 32-bit) that the
+ * clamp in global_node_page_state() would otherwise turn into a huge spurious
+ * delta. Do NOT use for non-monotonic page-count reads.
+ */
+static inline unsigned long global_node_page_state_monotonic(enum node_stat_item item)
+{
+	return (unsigned long)atomic_long_read(&vm_node_stat[item]);
+}
+
 static inline unsigned long global_node_page_state(enum node_stat_item item)
 {
 	VM_WARN_ON_ONCE(vmstat_item_in_bytes(item));
@@ -259,11 +271,14 @@ extern unsigned long node_page_state(struct pglist_data *pgdat,
 						enum node_stat_item item);
 extern unsigned long node_page_state_pages(struct pglist_data *pgdat,
 					   enum node_stat_item item);
+extern unsigned long node_page_state_monotonic(struct pglist_data *pgdat,
+					       enum node_stat_item item);
 extern void fold_vm_numa_events(void);
 #else
 #define sum_zone_node_page_state(node, item) global_zone_page_state(item)
 #define node_page_state(node, item) global_node_page_state(item)
 #define node_page_state_pages(node, item) global_node_page_state_pages(item)
+#define node_page_state_monotonic(node, item) global_node_page_state_monotonic(item)
 static inline void fold_vm_numa_events(void)
 {
 }
diff --git a/lib/maple_tree.c b/lib/maple_tree.c
--- a/lib/maple_tree.c
+++ b/lib/maple_tree.c
@@ -1501,14 +1501,26 @@ static inline void mas_parent_gap(struct ma_state *mas, unsigned char offset,
 	goto ascend;
 }
 
+static __always_inline void mas_update_gap_known(struct ma_state *mas,
+		unsigned long gap)
+{
+	unsigned char pslot;
+	unsigned long p_gap;
+
+	pslot = mte_parent_slot(mas->node);
+	p_gap = ma_gaps(mte_parent(mas->node),
+			mas_parent_type(mas, mas->node))[pslot];
+
+	if (p_gap != gap)
+		mas_parent_gap(mas, pslot, gap);
+}
+
 /*
  * mas_update_gap() - Update a nodes gaps and propagate up if necessary.
  * @mas: the maple state.
  */
 static inline void mas_update_gap(struct ma_state *mas)
 {
-	unsigned char pslot;
-	unsigned long p_gap;
 	unsigned long max_gap;
 
 	if (!mt_is_alloc(mas->tree))
@@ -1518,13 +1530,7 @@ static inline void mas_update_gap(struct ma_state *mas)
 		return;
 
 	max_gap = mas_max_gap(mas);
-
-	pslot = mte_parent_slot(mas->node);
-	p_gap = ma_gaps(mte_parent(mas->node),
-			mas_parent_type(mas, mas->node))[pslot];
-
-	if (p_gap != max_gap)
-		mas_parent_gap(mas, pslot, max_gap);
+	mas_update_gap_known(mas, max_gap);
 }
 
 /*
@@ -2081,8 +2087,8 @@ static inline void mas_wmb_replace(struct ma_state *mas, struct maple_copy *cp)
 	mas->node = mt_slot_locked(mas->tree, cp->slot, 0);
 	/* Insert the new data in the tree */
 	mas_topiary_replace(mas, old_enode, cp->height);
-	if (!mte_is_leaf(mas->node))
-		mas_update_gap(mas);
+	if (mt_is_alloc(mas->tree) && !mte_is_root(mas->node))
+		mas_update_gap_known(mas, cp->gap[0]);
 
 	mtree_range_walk(mas);
 }
@@ -3125,7 +3131,7 @@ static void mas_wr_spanning_store(struct ma_wr_state *wr_mas)
 static inline void mas_wr_node_store(struct ma_wr_state *wr_mas)
 {
 	unsigned char dst_offset, offset_end;
-	unsigned char copy_size, node_pivots;
+	unsigned char copy_size, node_pivots, node_slots;
 	struct maple_node reuse, *newnode;
 	unsigned long *dst_pivots;
 	void __rcu **dst_slots;
@@ -3138,6 +3144,7 @@ static inline void mas_wr_node_store(struct ma_wr_state *wr_mas)
 	in_rcu = mt_in_rcu(mas->tree);
 	offset_end = wr_mas->offset_end;
 	node_pivots = mt_pivots[wr_mas->type];
+	node_slots = mt_slots[wr_mas->type];
 	/* Assume last adds an entry */
 	new_end = mas->end + 1 - offset_end + mas->offset;
 	if (mas->last == wr_mas->end_piv) {
@@ -3149,7 +3156,6 @@ static inline void mas_wr_node_store(struct ma_wr_state *wr_mas)
 	if (in_rcu) {
 		newnode = mas_pop_node(mas);
 	} else {
-		memset(&reuse, 0, sizeof(struct maple_node));
 		newnode = &reuse;
 	}
 
@@ -3193,7 +3199,21 @@ static inline void mas_wr_node_store(struct ma_wr_state *wr_mas)
 		dst_pivots[new_end] = mas->max;
 
 done:
-	mas_leaf_set_meta(newnode, maple_leaf_64, new_end);
+	if (!in_rcu && new_end + 2 < node_slots) {
+		unsigned char clear_from = new_end + 1;
+
+		/*
+		 * Note that the last slot is never cleared, since the metadata
+		 * will be stored there or it has a value.
+		 */
+		memset(dst_slots + clear_from, 0,
+		       sizeof(void __rcu *) * (node_slots - clear_from));
+		if (clear_from < node_pivots)
+			memset(dst_pivots + clear_from, 0,
+			       sizeof(unsigned long) * (node_pivots - clear_from));
+	}
+
+	mas_leaf_set_meta(newnode, wr_mas->type, new_end);
 	if (in_rcu) {
 		struct maple_enode *old_enode = mas->node;
 
@@ -3218,7 +3238,7 @@ static inline void mas_wr_slot_store(struct ma_wr_state *wr_mas)
 	void __rcu **slots = wr_mas->slots;
 	bool gap = false;
 
-	gap |= !mt_slot_locked(mas->tree, slots, offset);
+	gap |= !wr_mas->content;
 	gap |= !mt_slot_locked(mas->tree, slots, offset + 1);
 
 	if (wr_mas->offset_end - offset == 1) {
@@ -3661,6 +3681,9 @@ static inline enum store_type mas_wr_store_type(struct ma_wr_state *wr_mas)
 {
 	struct ma_state *mas = wr_mas->mas;
 	unsigned char new_end;
+	bool appending;
+	bool one_slot;
+	bool in_rcu;
 
 	if (unlikely(mas_is_none(mas) || mas_is_ptr(mas)))
 		return wr_store_root;
@@ -3680,21 +3703,30 @@ static inline enum store_type mas_wr_store_type(struct ma_wr_state *wr_mas)
 		return wr_new_root;
 
 	new_end = mas_wr_new_end(wr_mas);
+	in_rcu = mt_in_rcu(mas->tree);
+	appending = mas->offset == mas->end;
+	one_slot = wr_mas->offset_end - mas->offset == 1;
+
 	/* Potential spanning rebalance collapsing a node */
 	if (new_end < mt_min_slots[wr_mas->type]) {
 		if (!mte_is_root(mas->node))
 			return  wr_rebalance;
+		if (!in_rcu) {
+			if (appending)
+				return wr_append;
+			else if (mas->end == new_end && one_slot)
+				return wr_slot_store;
+		}
 		return wr_node_store;
 	}
 
 	if (new_end >= mt_slots[wr_mas->type])
 		return wr_split_store;
 
-	if (!mt_in_rcu(mas->tree) && (mas->offset == mas->end))
+	if (!in_rcu && appending)
 		return wr_append;
 
-	if ((new_end == mas->end) && (!mt_in_rcu(mas->tree) ||
-		(wr_mas->offset_end - mas->offset == 1)))
+	if (new_end == mas->end && (!in_rcu || one_slot))
 		return wr_slot_store;
 
 	return wr_node_store;
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1442,10 +1442,10 @@ static enum scan_result collapse_huge_page(struct mm_struct *mm, unsigned long s
 
 	result = SCAN_SUCCEED;
 out_up_write:
-	if (anon_vma_locked)
-		anon_vma_unlock_write(vma->anon_vma);
 	if (pte)
 		pte_unmap(pte);
+	if (anon_vma_locked)
+		anon_vma_unlock_write(vma->anon_vma);
 	mmap_write_unlock(mm);
 out_nolock:
 	if (folio)
diff --git a/mm/ksm.c b/mm/ksm.c
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -3061,10 +3061,9 @@ int __ksm_enter(struct mm_struct *mm)
 
 	slot = &mm_slot->slot;
 
+	spin_lock(&ksm_mmlist_lock);
 	/* Check ksm_run too?  Would need tighter locking */
 	needs_wakeup = list_empty(&ksm_mm_head.slot.mm_node);
-
-	spin_lock(&ksm_mmlist_lock);
 	mm_slot_insert(mm_slots_hash, mm, slot);
 	/*
 	 * When KSM_RUN_MERGE (or KSM_RUN_STOP),
diff --git a/mm/memcontrol-v1.c b/mm/memcontrol-v1.c
--- a/mm/memcontrol-v1.c
+++ b/mm/memcontrol-v1.c
@@ -1998,8 +1998,8 @@ void memcg1_stat_format(struct mem_cgroup *memcg, struct seq_buf *s)
 		for_each_online_pgdat(pgdat) {
 			mz = memcg->nodeinfo[pgdat->node_id];
 
-			anon_cost += mz->lruvec.anon_cost;
-			file_cost += mz->lruvec.file_cost;
+			anon_cost += mz->lruvec.cost[WORKINGSET_ANON].count;
+			file_cost += mz->lruvec.cost[WORKINGSET_FILE].count;
 		}
 		seq_buf_printf(s, "anon_cost %lu\n", anon_cost);
 		seq_buf_printf(s, "file_cost %lu\n", file_cost);
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -393,6 +393,7 @@ static const unsigned int memcg_node_stat_items[] = {
 	NR_SHMEM_THPS,
 	NR_FILE_THPS,
 	NR_ANON_THPS,
+	NR_VMSCAN_WRITE,
 	NR_VMALLOC,
 	NR_KERNEL_STACK_KB,
 	NR_PAGETABLE,
@@ -419,6 +420,8 @@ static const unsigned int memcg_node_stat_items[] = {
 	PGSCAN_PROACTIVE,
 	PGSCAN_ANON,
 	PGSCAN_FILE,
+	PGROTATE_ANON,
+	PGROTATE_FILE,
 	PGREFILL,
 #ifdef CONFIG_HUGETLB_PAGE
 	NR_HUGETLB,
@@ -502,6 +505,42 @@ unsigned long lruvec_page_state(struct lruvec *lruvec, enum node_stat_item idx)
 	return x;
 }
 
+/**
+ * lruvec_page_state_monotonic - non-clamping lruvec stat read for delta sampling
+ * @lruvec: the LRU vector to read from
+ * @idx: the node_stat_item to read
+ *
+ * Returns the raw state[idx] value cast to unsigned long, skipping the
+ * clamp-negative-to-zero step in lruvec_page_state(). Intended for callers
+ * that snapshot a monotonically-incremented counter and subtract two
+ * samples: unsigned modular arithmetic then yields the correct delta across
+ * a signed-long wraparound (a real hazard on 32-bit) that the clamp would
+ * otherwise turn into a huge spurious delta.
+ *
+ * Do NOT use for non-monotonic page-count reads where a transient negative
+ * reading from per-CPU delta skew must present as zero.
+ *
+ * XXX: This helper (and its node/global peers) exists because some
+ * monotonically-incremented event counters are stored in
+ * enum node_stat_item.
+ */
+unsigned long lruvec_page_state_monotonic(struct lruvec *lruvec,
+					  enum node_stat_item idx)
+{
+	struct mem_cgroup_per_node *pn;
+	int i;
+
+	if (mem_cgroup_disabled())
+		return node_page_state_monotonic(lruvec_pgdat(lruvec), idx);
+
+	i = memcg_stats_index(idx);
+	if (WARN_ONCE(BAD_STAT_IDX(i), "%s: missing stat item %d\n", __func__, idx))
+		return 0;
+
+	pn = container_of(lruvec, struct mem_cgroup_per_node, lruvec);
+	return (unsigned long)READ_ONCE(pn->lruvec_stats->state[i]);
+}
+
 unsigned long lruvec_page_state_local(struct lruvec *lruvec,
 				      enum node_stat_item idx)
 {
@@ -2095,7 +2134,12 @@ static bool consume_stock(struct mem_cgroup *memcg, unsigned int nr_pages)
 
 		stock_pages = READ_ONCE(stock->nr_pages[i]);
 		if (stock_pages >= nr_pages) {
-			WRITE_ONCE(stock->nr_pages[i], stock_pages - nr_pages);
+			stock_pages -= nr_pages;
+			WRITE_ONCE(stock->nr_pages[i], stock_pages);
+			if (!stock_pages) {
+				css_put(&memcg->css);
+				WRITE_ONCE(stock->cached[i], NULL);
+			}
 			ret = true;
 		}
 		break;
diff --git a/mm/migrate_device.c b/mm/migrate_device.c
--- a/mm/migrate_device.c
+++ b/mm/migrate_device.c
@@ -872,7 +872,7 @@ static int migrate_vma_insert_huge_pmd_page(struct migrate_vma *migrate,
 
 	if (flush) {
 		pte_free(vma->vm_mm, pgtable);
-		flush_cache_page(vma, addr, addr + HPAGE_PMD_SIZE);
+		flush_cache_range(vma, addr, addr + HPAGE_PMD_SIZE);
 		pmdp_invalidate(vma, addr, pmdp);
 	} else {
 		pgtable_trans_huge_deposit(vma->vm_mm, pmdp, pgtable);
diff --git a/mm/mmzone.c b/mm/mmzone.c
--- a/mm/mmzone.c
+++ b/mm/mmzone.c
@@ -78,6 +78,7 @@ void lruvec_init(struct lruvec *lruvec)
 
 	memset(lruvec, 0, sizeof(struct lruvec));
 	spin_lock_init(&lruvec->lru_lock);
+	spin_lock_init(&lruvec->cost_lock);
 	zswap_lruvec_state_init(lruvec);
 
 	for_each_lru(lru)
diff --git a/mm/mremap.c b/mm/mremap.c
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -264,7 +264,7 @@ static int move_ptes(struct pagetable_move_control *pmc,
 
 	for (; old_addr < old_end; old_ptep += nr_ptes, old_addr += nr_ptes * PAGE_SIZE,
 		new_ptep += nr_ptes, new_addr += nr_ptes * PAGE_SIZE) {
-		VM_WARN_ON_ONCE(!pte_none(*new_ptep));
+		VM_WARN_ON_ONCE(!pte_none(ptep_get(new_ptep)));
 
 		nr_ptes = 1;
 		max_nr_ptes = (old_end - old_addr) >> PAGE_SHIFT;
diff --git a/mm/shmem.c b/mm/shmem.c
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -3612,6 +3612,7 @@ static long shmem_fallocate(struct file *file, int mode, loff_t offset,
 	struct shmem_inode_info *info = SHMEM_I(inode);
 	struct shmem_falloc shmem_falloc;
 	pgoff_t start, index, end, undo_fallocend;
+	loff_t aligned_end;
 	int error;
 
 	if (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE))
@@ -3668,8 +3669,15 @@ static long shmem_fallocate(struct file *file, int mode, loff_t offset,
 		goto out;
 	}
 
+	/* Check for wraparound */
+	if (check_add_overflow(offset + len, (loff_t)PAGE_SIZE - 1,
+			       &aligned_end)) {
+		error = -EFBIG;
+		goto out;
+	}
+
 	start = offset >> PAGE_SHIFT;
-	end = (offset + len + PAGE_SIZE - 1) >> PAGE_SHIFT;
+	end = aligned_end >> PAGE_SHIFT;
 	/* Try to avoid a swapstorm if len is impossible to satisfy */
 	if (sbinfo->max_blocks && end - start > sbinfo->max_blocks) {
 		error = -ENOSPC;
diff --git a/mm/swap.c b/mm/swap.c
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -272,73 +272,6 @@ void folio_rotate_reclaimable(struct folio *folio)
 	folio_batch_add_and_move(folio, lru_move_tail);
 }
 
-void lru_note_cost_unlock_irq(struct lruvec *lruvec, bool file,
-		unsigned int nr_io, unsigned int nr_rotated)
-		__releases(lruvec->lru_lock)
-		__releases(rcu)
-{
-	unsigned long cost;
-
-	/*
-	 * Reflect the relative cost of incurring IO and spending CPU
-	 * time on rotations. This doesn't attempt to make a precise
-	 * comparison, it just says: if reloads are about comparable
-	 * between the LRU lists, or rotations are overwhelmingly
-	 * different between them, adjust scan balance for CPU work.
-	 */
-	cost = nr_io * SWAP_CLUSTER_MAX + nr_rotated;
-	if (!cost) {
-		spin_unlock_irq(&lruvec->lru_lock);
-		rcu_read_unlock();
-		return;
-	}
-
-	for (;;) {
-		unsigned long lrusize;
-
-		/* Record cost event */
-		if (file)
-			lruvec->file_cost += cost;
-		else
-			lruvec->anon_cost += cost;
-
-		/*
-		 * Decay previous events
-		 *
-		 * Because workloads change over time (and to avoid
-		 * overflow) we keep these statistics as a floating
-		 * average, which ends up weighing recent refaults
-		 * more than old ones.
-		 */
-		lrusize = lruvec_page_state(lruvec, NR_INACTIVE_ANON) +
-			  lruvec_page_state(lruvec, NR_ACTIVE_ANON) +
-			  lruvec_page_state(lruvec, NR_INACTIVE_FILE) +
-			  lruvec_page_state(lruvec, NR_ACTIVE_FILE);
-
-		if (lruvec->file_cost + lruvec->anon_cost > lrusize / 4) {
-			lruvec->file_cost /= 2;
-			lruvec->anon_cost /= 2;
-		}
-
-		spin_unlock_irq(&lruvec->lru_lock);
-		lruvec = parent_lruvec(lruvec);
-		if (!lruvec) {
-			rcu_read_unlock();
-			break;
-		}
-		spin_lock_irq(&lruvec->lru_lock);
-	}
-}
-
-void lru_note_cost_refault(struct folio *folio)
-{
-	struct lruvec *lruvec;
-
-	lruvec = folio_lruvec_lock_irq(folio);
-	lru_note_cost_unlock_irq(lruvec, folio_is_file_lru(folio),
-				folio_nr_pages(folio), 0);
-}
-
 static void lru_activate(struct lruvec *lruvec, struct folio *folio)
 {
 	long nr_pages = folio_nr_pages(folio);
@@ -1173,8 +1106,6 @@ void lru_reparent_memcg(struct mem_cgroup *memcg, struct mem_cgroup *parent, int
 
 	child_lruvec = mem_cgroup_lruvec(memcg, NODE_DATA(nid));
 	parent_lruvec = mem_cgroup_lruvec(parent, NODE_DATA(nid));
-	parent_lruvec->anon_cost += child_lruvec->anon_cost;
-	parent_lruvec->file_cost += child_lruvec->file_cost;
 
 	for_each_lru(lru)
 		lruvec_reparent_lru(child_lruvec, parent_lruvec, lru, nid);
diff --git a/mm/vma.c b/mm/vma.c
--- a/mm/vma.c
+++ b/mm/vma.c
@@ -1866,10 +1866,10 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap,
 	bool *need_rmap_locks)
 {
 	struct vm_area_struct *vma = *vmap;
-	unsigned long vma_start = vma->vm_start;
+	unsigned long old_vma_start = vma->vm_start;
 	struct mm_struct *mm = vma->vm_mm;
 	struct vm_area_struct *new_vma;
-	bool faulted_in_anon_vma = true;
+	bool can_self_merge = false;
 	VMA_ITERATOR(vmi, mm, addr);
 	VMG_VMA_STATE(vmg, &vmi, NULL, vma, addr, addr + len);
 
@@ -1879,7 +1879,7 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap,
 	 */
 	if (unlikely(vma_is_anonymous(vma) && !vma->anon_vma)) {
 		pgoff = addr >> PAGE_SHIFT;
-		faulted_in_anon_vma = false;
+		can_self_merge = true;
 	}
 
 	/*
@@ -1899,24 +1899,21 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap,
 	new_vma = vma_merge_copied_range(&vmg);
 
 	if (new_vma) {
-		/*
-		 * Source vma may have been merged into new_vma
-		 */
-		if (unlikely(vma_start >= new_vma->vm_start &&
-			     vma_start < new_vma->vm_end)) {
+		/* Self-merged and VMA replaced. */
+		if (unlikely(new_vma->vm_start < old_vma_start &&
+			     new_vma->vm_end > old_vma_start)) {
 			/*
-			 * The only way we can get a vma_merge with
-			 * self during an mremap is if the vma hasn't
-			 * been faulted in yet and we were allowed to
-			 * reset the dst vma->vm_pgoff to the
-			 * destination address of the mremap to allow
-			 * the merge to happen. mremap must change the
-			 * vm_pgoff linearity between src and dst vmas
-			 * (in turn preventing a vma_merge) to be
-			 * safe. It is only safe to keep the vm_pgoff
-			 * linear if there are no pages mapped yet.
+			 * The only way a VMA can both self-merge and be
+			 * replaced is if the remap places the new VMA
+			 * immediately prior to its old self ('next') and
+			 * immediately after another VMA ('prev') causing the
+			 * next to be removed and prev to be expanded to cover
+			 * the entire range.
+			 *
+			 * This should only be possible if the page offset was
+			 * updated, i.e. the VMA is unfaulted.
 			 */
-			VM_BUG_ON_VMA(faulted_in_anon_vma, new_vma);
+			VM_WARN_ON_ONCE_VMA(!can_self_merge, new_vma);
 			*vmap = vma = new_vma;
 		}
 		*need_rmap_locks = (new_vma->vm_pgoff <= vma->vm_pgoff);
diff --git a/mm/vmscan.c b/mm/vmscan.c
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -669,7 +669,7 @@ static pageout_t pageout(struct folio *folio, struct address_space *mapping,
 		folio_clear_reclaim(folio);
 
 	trace_mm_vmscan_write_folio(folio);
-	node_stat_add_folio(folio, NR_VMSCAN_WRITE);
+	lruvec_stat_mod_folio(folio, NR_VMSCAN_WRITE, folio_nr_pages(folio));
 	return PAGE_SUCCESS;
 }
 
@@ -1420,8 +1420,6 @@ static unsigned int shrink_folio_list(struct list_head *folio_list,
 					sc->nr_scanned -= (nr_pages - 1);
 					nr_pages = 1;
 				}
-				stat->nr_pageout += nr_pages;
-
 				if (folio_test_writeback(folio))
 					goto keep;
 				if (folio_test_dirty(folio))
@@ -2045,10 +2043,10 @@ static unsigned long shrink_inactive_list(unsigned long nr_to_scan,
 	item = PGSTEAL_KSWAPD + reclaimer_offset(sc);
 	mod_lruvec_state(lruvec, item, nr_reclaimed);
 	mod_lruvec_state(lruvec, PGSTEAL_ANON + file, nr_reclaimed);
+	if (nr_scanned > nr_reclaimed)
+		mod_lruvec_state(lruvec, PGROTATE_ANON + file,
+				 nr_scanned - nr_reclaimed);
 
-	lruvec_lock_irq(lruvec);
-	lru_note_cost_unlock_irq(lruvec, file, stat.nr_pageout,
-					nr_scanned - nr_reclaimed);
 	handle_reclaim_writeback(nr_taken, pgdat, sc, &stat);
 	trace_mm_vmscan_lru_shrink_inactive(pgdat->node_id,
 			nr_scanned, nr_reclaimed, &stat, sc->priority, file);
@@ -2154,9 +2152,9 @@ static void shrink_active_list(unsigned long nr_to_scan,
 	count_vm_events(PGDEACTIVATE, nr_deactivate);
 	count_memcg_events(lruvec_memcg(lruvec), PGDEACTIVATE, nr_deactivate);
 	mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, -nr_taken);
+	if (nr_rotated)
+		mod_lruvec_state(lruvec, PGROTATE_ANON + file, nr_rotated);
 
-	lruvec_lock_irq(lruvec);
-	lru_note_cost_unlock_irq(lruvec, file, 0, nr_rotated);
 	trace_mm_vmscan_lru_shrink_active(pgdat->node_id, nr_taken, nr_activate,
 			nr_deactivate, nr_rotated, sc->priority, file);
 }
@@ -2289,8 +2287,10 @@ enum scan_balance {
 
 static void prepare_scan_control(pg_data_t *pgdat, struct scan_control *sc)
 {
-	unsigned long file;
+	struct lru_cost *anon_cost, *file_cost;
 	struct lruvec *target_lruvec;
+	unsigned long lrusize;
+	unsigned long file;
 
 	if (lru_gen_enabled() && !lru_gen_switching())
 		return;
@@ -2306,11 +2306,69 @@ static void prepare_scan_control(pg_data_t *pgdat, struct scan_control *sc)
 
 	/*
 	 * Determine the scan balance between anon and file LRUs.
+	 *
+	 * The cost model is based on rotations, refaults and
+	 * reclaim-driven writes (anon only) on each side.
+	 *
+	 * These event counters are monotonic, so each reclaim cycle
+	 * the delta since the last scan is extracted and incorporated
+	 * into a decaying average. This ensures currency, as workloads
+	 * change over time, and avoids overflow in the calculations.
+	 *
+	 * Use lruvec_page_state_monotonic() so unsigned subtraction
+	 * yields the correct delta across a signed-long wraparound of
+	 * the underlying counter (a real hazard on 32-bit that the
+	 * clamp in lruvec_page_state() would otherwise turn into a huge
+	 * spurious delta).
 	 */
-	spin_lock_irq(&target_lruvec->lru_lock);
-	sc->anon_cost = target_lruvec->anon_cost;
-	sc->file_cost = target_lruvec->file_cost;
-	spin_unlock_irq(&target_lruvec->lru_lock);
+	spin_lock(&target_lruvec->cost_lock);
+
+	for (int f = 0; f <= 1; f++) {
+		struct lru_cost *cost = &target_lruvec->cost[f];
+		unsigned long rotated, io, nr_rotated, nr_io;
+
+		rotated = lruvec_page_state_monotonic(target_lruvec,
+						      PGROTATE_ANON + f);
+		io = lruvec_page_state_monotonic(target_lruvec,
+						 WORKINGSET_RESTORE_BASE + f);
+		if (f == WORKINGSET_ANON)
+			io += lruvec_page_state_monotonic(target_lruvec,
+							  NR_VMSCAN_WRITE);
+
+		nr_rotated = rotated - cost->last_rotated;
+		nr_io = io - cost->last_io;
+
+		/*
+		 * Reflect the relative cost of incurring IO and spending
+		 * CPU time on rotations. This doesn't attempt to make a
+		 * precise comparison, it just says: if reloads are about
+		 * comparable between the LRU lists, or rotations are
+		 * overwhelmingly different between them, adjust scan
+		 * balance for CPU work.
+		 */
+		cost->count += nr_io * SWAP_CLUSTER_MAX + nr_rotated;
+
+		cost->last_rotated = rotated;
+		cost->last_io = io;
+	}
+
+	anon_cost = &target_lruvec->cost[WORKINGSET_ANON];
+	file_cost = &target_lruvec->cost[WORKINGSET_FILE];
+
+	lrusize = lruvec_page_state(target_lruvec, NR_INACTIVE_ANON) +
+		  lruvec_page_state(target_lruvec, NR_ACTIVE_ANON) +
+		  lruvec_page_state(target_lruvec, NR_INACTIVE_FILE) +
+		  lruvec_page_state(target_lruvec, NR_ACTIVE_FILE);
+
+	while (anon_cost->count + file_cost->count > lrusize / 4) {
+		anon_cost->count /= 2;
+		file_cost->count /= 2;
+	}
+
+	sc->anon_cost = anon_cost->count;
+	sc->file_cost = file_cost->count;
+
+	spin_unlock(&target_lruvec->cost_lock);
 
 	/*
 	 * Target desirable inactive:active list ratios for the anon
@@ -4197,7 +4255,7 @@ bool lru_gen_look_around(struct page_vma_mapped_walk *pvmw, unsigned int nr)
 	unsigned long end;
 	struct lru_gen_mm_walk *walk;
 	struct folio *last = NULL;
-	int young = 1;
+	int young = nr;
 	pte_t *pte = pvmw->pte;
 	unsigned long addr = pvmw->address;
 	struct vm_area_struct *vma = pvmw->vma;
@@ -4819,7 +4877,8 @@ static int evict_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
 	struct reclaim_stat stat;
 	struct lru_gen_mm_walk *walk;
 	int scanned, reclaimed;
-	int isolated = 0, type, type_scanned;
+	int isolated = 0, nr_isolated = 0, type, type_scanned;
+	unsigned long total_reclaimed = 0;
 	bool skip_retry = false;
 	struct mem_cgroup *memcg = lruvec_memcg(lruvec);
 	struct pglist_data *pgdat = lruvec_pgdat(lruvec);
@@ -4831,6 +4890,7 @@ static int evict_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
 
 	scanned = isolate_folios(nr_to_scan, lruvec, sc, swappiness,
 				 &list, &isolated, &type, &type_scanned);
+	nr_isolated = isolated;
 
 	/* Scanning may have emptied the oldest gen, flush it */
 	if (scanned)
@@ -4843,6 +4903,7 @@ static int evict_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
 retry:
 	reclaimed = shrink_folio_list(&list, pgdat, sc, &stat, false, memcg);
 	sc->nr_reclaimed += reclaimed;
+	total_reclaimed += reclaimed;
 	/* Retry pass is only meant for clean folios without new isolation */
 	if (isolated)
 		handle_reclaim_writeback(isolated, pgdat, sc, &stat);
@@ -4892,6 +4953,10 @@ static int evict_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
 		goto retry;
 	}
 
+	if (nr_isolated > total_reclaimed)
+		mod_lruvec_state(lruvec, PGROTATE_ANON + type,
+				 nr_isolated - total_reclaimed);
+
 	return scanned;
 }
 
diff --git a/mm/vmstat.c b/mm/vmstat.c
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1024,6 +1024,17 @@ unsigned long node_page_state(struct pglist_data *pgdat,
 
 	return node_page_state_pages(pgdat, item);
 }
+
+/*
+ * Non-clamping variant of node_page_state() intended for callers that
+ * snapshot a monotonically-incremented counter and subtract two samples.
+ * See global_node_page_state_monotonic() for the rationale.
+ */
+unsigned long node_page_state_monotonic(struct pglist_data *pgdat,
+					enum node_stat_item item)
+{
+	return (unsigned long)atomic_long_read(&pgdat->vm_stat[item]);
+}
 #endif
 
 /*
@@ -1289,6 +1300,8 @@ const char * const vmstat_text[] = {
 	[I(PGSCAN_PROACTIVE)]			= "pgscan_proactive",
 	[I(PGSCAN_ANON)]			= "pgscan_anon",
 	[I(PGSCAN_FILE)]			= "pgscan_file",
+	[I(PGROTATE_ANON)]			= "pgrotate_anon",
+	[I(PGROTATE_FILE)]			= "pgrotate_file",
 	[I(PGREFILL)]				= "pgrefill",
 #ifdef CONFIG_HUGETLB_PAGE
 	[I(NR_HUGETLB)]				= "nr_hugetlb",
diff --git a/mm/workingset.c b/mm/workingset.c
--- a/mm/workingset.c
+++ b/mm/workingset.c
@@ -584,11 +584,6 @@ void workingset_refault(struct folio *folio, void *shadow)
 	/* Folio was active prior to eviction */
 	if (workingset) {
 		folio_set_workingset(folio);
-		/*
-		 * XXX: Move to folio_add_lru() when it supports new vs
-		 * putback
-		 */
-		lru_note_cost_refault(folio);
 		mod_lruvec_state(lruvec, WORKINGSET_RESTORE_BASE + file, nr);
 	}
 out:
diff --git a/mm/zswap.c b/mm/zswap.c
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -1217,7 +1217,7 @@ static unsigned long zswap_shrinker_count(struct shrinker *shrinker,
 	 * Without memcg, use the zswap pool-wide metrics.
 	 */
 	if (!mem_cgroup_disabled()) {
-		mem_cgroup_flush_stats(memcg);
+		mem_cgroup_flush_stats_ratelimited(memcg);
 		nr_backing = memcg_page_state(memcg, MEMCG_ZSWAP_B) >> PAGE_SHIFT;
 		nr_stored = memcg_page_state(memcg, MEMCG_ZSWAPPED);
 	} else {
@@ -1275,6 +1275,14 @@ static struct shrinker *zswap_alloc_shrinker(void)
 	return shrinker;
 }
 
+/*
+ * Scan up to SWAP_CLUSTER_MAX pages on each per-node zswap LRU of @memcg
+ * and write back the reclaimable ones.
+ *
+ * Return: 0 if at least one entry was written back, -EAGAIN if entries
+ * were scanned but none could be written back, or -ENOENT if @memcg has
+ * writeback disabled, is a zombie cgroup, or has empty zswap LRUs.
+ */
 static int shrink_memcg(struct mem_cgroup *memcg)
 {
 	int nid, shrunk = 0, scanned = 0;
@@ -1290,13 +1298,14 @@ static int shrink_memcg(struct mem_cgroup *memcg)
 		return -ENOENT;
 
 	for_each_node_state(nid, N_NORMAL_MEMORY) {
-		unsigned long nr_to_walk = 1;
+		unsigned long nr_to_walk = SWAP_CLUSTER_MAX;
 
 		shrunk += list_lru_walk_one(&zswap_list_lru, nid, memcg,
 					    &shrink_memcg_cb, NULL, &nr_to_walk);
-		scanned += 1 - nr_to_walk;
+		scanned += SWAP_CLUSTER_MAX - nr_to_walk;
 	}
 
+	/* Nothing was scanned: every LRU under @memcg was empty. */
 	if (!scanned)
 		return -ENOENT;