Adding upstream version 6.8.9.upstream/6.8.9

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 242 insertions, 134 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 27c9f451d4..61932c9215 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -64,6 +64,7 @@
 #include <linux/psi.h>
 #include <linux/seq_buf.h>
 #include <linux/sched/isolation.h>
+#include <linux/kmemleak.h>
 #include "internal.h"
 #include <net/sock.h>
 #include <net/ip.h>
@@ -573,116 +574,6 @@ mem_cgroup_largest_soft_limit_node(struct mem_cgroup_tree_per_node *mctz)
 	return mz;
 }
 
-/*
- * memcg and lruvec stats flushing
- *
- * Many codepaths leading to stats update or read are performance sensitive and
- * adding stats flushing in such codepaths is not desirable. So, to optimize the
- * flushing the kernel does:
- *
- * 1) Periodically and asynchronously flush the stats every 2 seconds to not let
- *    rstat update tree grow unbounded.
- *
- * 2) Flush the stats synchronously on reader side only when there are more than
- *    (MEMCG_CHARGE_BATCH * nr_cpus) update events. Though this optimization
- *    will let stats be out of sync by atmost (MEMCG_CHARGE_BATCH * nr_cpus) but
- *    only for 2 seconds due to (1).
- */
-static void flush_memcg_stats_dwork(struct work_struct *w);
-static DECLARE_DEFERRABLE_WORK(stats_flush_dwork, flush_memcg_stats_dwork);
-static DEFINE_PER_CPU(unsigned int, stats_updates);
-static atomic_t stats_flush_ongoing = ATOMIC_INIT(0);
-static atomic_t stats_flush_threshold = ATOMIC_INIT(0);
-static u64 flush_next_time;
-
-#define FLUSH_TIME (2UL*HZ)
-
-/*
- * Accessors to ensure that preemption is disabled on PREEMPT_RT because it can
- * not rely on this as part of an acquired spinlock_t lock. These functions are
- * never used in hardirq context on PREEMPT_RT and therefore disabling preemtion
- * is sufficient.
- */
-static void memcg_stats_lock(void)
-{
-	preempt_disable_nested();
-	VM_WARN_ON_IRQS_ENABLED();
-}
-
-static void __memcg_stats_lock(void)
-{
-	preempt_disable_nested();
-}
-
-static void memcg_stats_unlock(void)
-{
-	preempt_enable_nested();
-}
-
-static inline void memcg_rstat_updated(struct mem_cgroup *memcg, int val)
-{
-	unsigned int x;
-
-	if (!val)
-		return;
-
-	cgroup_rstat_updated(memcg->css.cgroup, smp_processor_id());
-
-	x = __this_cpu_add_return(stats_updates, abs(val));
-	if (x > MEMCG_CHARGE_BATCH) {
-		/*
-		 * If stats_flush_threshold exceeds the threshold
-		 * (>num_online_cpus()), cgroup stats update will be triggered
-		 * in __mem_cgroup_flush_stats(). Increasing this var further
-		 * is redundant and simply adds overhead in atomic update.
-		 */
-		if (atomic_read(&stats_flush_threshold) <= num_online_cpus())
-			atomic_add(x / MEMCG_CHARGE_BATCH, &stats_flush_threshold);
-		__this_cpu_write(stats_updates, 0);
-	}
-}
-
-static void do_flush_stats(void)
-{
-	/*
-	 * We always flush the entire tree, so concurrent flushers can just
-	 * skip. This avoids a thundering herd problem on the rstat global lock
-	 * from memcg flushers (e.g. reclaim, refault, etc).
-	 */
-	if (atomic_read(&stats_flush_ongoing) ||
-	    atomic_xchg(&stats_flush_ongoing, 1))
-		return;
-
-	WRITE_ONCE(flush_next_time, jiffies_64 + 2*FLUSH_TIME);
-
-	cgroup_rstat_flush(root_mem_cgroup->css.cgroup);
-
-	atomic_set(&stats_flush_threshold, 0);
-	atomic_set(&stats_flush_ongoing, 0);
-}
-
-void mem_cgroup_flush_stats(void)
-{
-	if (atomic_read(&stats_flush_threshold) > num_online_cpus())
-		do_flush_stats();
-}
-
-void mem_cgroup_flush_stats_ratelimited(void)
-{
-	if (time_after64(jiffies_64, READ_ONCE(flush_next_time)))
-		mem_cgroup_flush_stats();
-}
-
-static void flush_memcg_stats_dwork(struct work_struct *w)
-{
-	/*
-	 * Always flush here so that flushing in latency-sensitive paths is
-	 * as cheap as possible.
-	 */
-	do_flush_stats();
-	queue_delayed_work(system_unbound_wq, &stats_flush_dwork, FLUSH_TIME);
-}
-
 /* Subset of vm_event_item to report for memcg event stats */
 static const unsigned int memcg_vm_event_stat[] = {
 	PGPGIN,
@@ -703,6 +594,7 @@ static const unsigned int memcg_vm_event_stat[] = {
 #if defined(CONFIG_MEMCG_KMEM) && defined(CONFIG_ZSWAP)
 	ZSWPIN,
 	ZSWPOUT,
+	ZSWPWB,
 #endif
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 	THP_FAULT_ALLOC,
@@ -729,6 +621,15 @@ static inline int memcg_events_index(enum vm_event_item idx)
 }
 
 struct memcg_vmstats_percpu {
+	/* Stats updates since the last flush */
+	unsigned int			stats_updates;
+
+	/* Cached pointers for fast iteration in memcg_rstat_updated() */
+	struct memcg_vmstats_percpu	*parent;
+	struct memcg_vmstats		*vmstats;
+
+	/* The above should fit a single cacheline for memcg_rstat_updated() */
+
 	/* Local (CPU and cgroup) page state & events */
 	long			state[MEMCG_NR_STAT];
 	unsigned long		events[NR_MEMCG_EVENTS];
@@ -740,7 +641,7 @@ struct memcg_vmstats_percpu {
 	/* Cgroup1: threshold notifications & softlimit tree updates */
 	unsigned long		nr_page_events;
 	unsigned long		targets[MEM_CGROUP_NTARGETS];
-};
+} ____cacheline_aligned;
 
 struct memcg_vmstats {
 	/* Aggregated (CPU and subtree) page state & events */
@@ -754,8 +655,133 @@ struct memcg_vmstats {
 	/* Pending child counts during tree propagation */
 	long			state_pending[MEMCG_NR_STAT];
 	unsigned long		events_pending[NR_MEMCG_EVENTS];
+
+	/* Stats updates since the last flush */
+	atomic64_t		stats_updates;
 };
 
+/*
+ * memcg and lruvec stats flushing
+ *
+ * Many codepaths leading to stats update or read are performance sensitive and
+ * adding stats flushing in such codepaths is not desirable. So, to optimize the
+ * flushing the kernel does:
+ *
+ * 1) Periodically and asynchronously flush the stats every 2 seconds to not let
+ *    rstat update tree grow unbounded.
+ *
+ * 2) Flush the stats synchronously on reader side only when there are more than
+ *    (MEMCG_CHARGE_BATCH * nr_cpus) update events. Though this optimization
+ *    will let stats be out of sync by atmost (MEMCG_CHARGE_BATCH * nr_cpus) but
+ *    only for 2 seconds due to (1).
+ */
+static void flush_memcg_stats_dwork(struct work_struct *w);
+static DECLARE_DEFERRABLE_WORK(stats_flush_dwork, flush_memcg_stats_dwork);
+static u64 flush_last_time;
+
+#define FLUSH_TIME (2UL*HZ)
+
+/*
+ * Accessors to ensure that preemption is disabled on PREEMPT_RT because it can
+ * not rely on this as part of an acquired spinlock_t lock. These functions are
+ * never used in hardirq context on PREEMPT_RT and therefore disabling preemtion
+ * is sufficient.
+ */
+static void memcg_stats_lock(void)
+{
+	preempt_disable_nested();
+	VM_WARN_ON_IRQS_ENABLED();
+}
+
+static void __memcg_stats_lock(void)
+{
+	preempt_disable_nested();
+}
+
+static void memcg_stats_unlock(void)
+{
+	preempt_enable_nested();
+}
+
+
+static bool memcg_vmstats_needs_flush(struct memcg_vmstats *vmstats)
+{
+	return atomic64_read(&vmstats->stats_updates) >
+		MEMCG_CHARGE_BATCH * num_online_cpus();
+}
+
+static inline void memcg_rstat_updated(struct mem_cgroup *memcg, int val)
+{
+	struct memcg_vmstats_percpu *statc;
+	int cpu = smp_processor_id();
+
+	if (!val)
+		return;
+
+	cgroup_rstat_updated(memcg->css.cgroup, cpu);
+	statc = this_cpu_ptr(memcg->vmstats_percpu);
+	for (; statc; statc = statc->parent) {
+		statc->stats_updates += abs(val);
+		if (statc->stats_updates < MEMCG_CHARGE_BATCH)
+			continue;
+
+		/*
+		 * If @memcg is already flush-able, increasing stats_updates is
+		 * redundant. Avoid the overhead of the atomic update.
+		 */
+		if (!memcg_vmstats_needs_flush(statc->vmstats))
+			atomic64_add(statc->stats_updates,
+				     &statc->vmstats->stats_updates);
+		statc->stats_updates = 0;
+	}
+}
+
+static void do_flush_stats(struct mem_cgroup *memcg)
+{
+	if (mem_cgroup_is_root(memcg))
+		WRITE_ONCE(flush_last_time, jiffies_64);
+
+	cgroup_rstat_flush(memcg->css.cgroup);
+}
+
+/*
+ * mem_cgroup_flush_stats - flush the stats of a memory cgroup subtree
+ * @memcg: root of the subtree to flush
+ *
+ * Flushing is serialized by the underlying global rstat lock. There is also a
+ * minimum amount of work to be done even if there are no stat updates to flush.
+ * Hence, we only flush the stats if the updates delta exceeds a threshold. This
+ * avoids unnecessary work and contention on the underlying lock.
+ */
+void mem_cgroup_flush_stats(struct mem_cgroup *memcg)
+{
+	if (mem_cgroup_disabled())
+		return;
+
+	if (!memcg)
+		memcg = root_mem_cgroup;
+
+	if (memcg_vmstats_needs_flush(memcg->vmstats))
+		do_flush_stats(memcg);
+}
+
+void mem_cgroup_flush_stats_ratelimited(struct mem_cgroup *memcg)
+{
+	/* Only flush if the periodic flusher is one full cycle late */
+	if (time_after64(jiffies_64, READ_ONCE(flush_last_time) + 2*FLUSH_TIME))
+		mem_cgroup_flush_stats(memcg);
+}
+
+static void flush_memcg_stats_dwork(struct work_struct *w)
+{
+	/*
+	 * Deliberately ignore memcg_vmstats_needs_flush() here so that flushing
+	 * in latency-sensitive paths is as cheap as possible.
+	 */
+	do_flush_stats(root_mem_cgroup);
+	queue_delayed_work(system_unbound_wq, &stats_flush_dwork, FLUSH_TIME);
+}
+
 unsigned long memcg_page_state(struct mem_cgroup *memcg, int idx)
 {
 	long x = READ_ONCE(memcg->vmstats->state[idx]);
@@ -870,16 +896,15 @@ void __mod_lruvec_state(struct lruvec *lruvec, enum node_stat_item idx,
 		__mod_memcg_lruvec_state(lruvec, idx, val);
 }
 
-void __mod_lruvec_page_state(struct page *page, enum node_stat_item idx,
+void __lruvec_stat_mod_folio(struct folio *folio, enum node_stat_item idx,
 			     int val)
 {
-	struct page *head = compound_head(page); /* rmap on tail pages */
 	struct mem_cgroup *memcg;
-	pg_data_t *pgdat = page_pgdat(page);
+	pg_data_t *pgdat = folio_pgdat(folio);
 	struct lruvec *lruvec;
 
 	rcu_read_lock();
-	memcg = page_memcg(head);
+	memcg = folio_memcg(folio);
 	/* Untracked pages have no memcg, no lruvec. Update only the node */
 	if (!memcg) {
 		rcu_read_unlock();
@@ -891,7 +916,7 @@ void __mod_lruvec_page_state(struct page *page, enum node_stat_item idx,
 	__mod_lruvec_state(lruvec, idx, val);
 	rcu_read_unlock();
 }
-EXPORT_SYMBOL(__mod_lruvec_page_state);
+EXPORT_SYMBOL(__lruvec_stat_mod_folio);
 
 void __mod_lruvec_kmem_state(void *p, enum node_stat_item idx, int val)
 {
@@ -1627,7 +1652,7 @@ static void memcg_stat_format(struct mem_cgroup *memcg, struct seq_buf *s)
 	 *
 	 * Current memory state:
 	 */
-	mem_cgroup_flush_stats();
+	mem_cgroup_flush_stats(memcg);
 
 	for (i = 0; i < ARRAY_SIZE(memory_stats); i++) {
 		u64 size;
@@ -2603,8 +2628,9 @@ static unsigned long calculate_high_delay(struct mem_cgroup *memcg,
 }
 
 /*
- * Scheduled by try_charge() to be executed from the userland return path
- * and reclaims memory over the high limit.
+ * Reclaims memory over the high limit. Called directly from
+ * try_charge() (context permitting), as well as from the userland
+ * return path where reclaim is always able to block.
  */
 void mem_cgroup_handle_over_high(gfp_t gfp_mask)
 {
@@ -2624,6 +2650,17 @@ void mem_cgroup_handle_over_high(gfp_t gfp_mask)
 
 retry_reclaim:
 	/*
+	 * Bail if the task is already exiting. Unlike memory.max,
+	 * memory.high enforcement isn't as strict, and there is no
+	 * OOM killer involved, which means the excess could already
+	 * be much bigger (and still growing) than it could for
+	 * memory.max; the dying task could get stuck in fruitless
+	 * reclaim for a long time, which isn't desirable.
+	 */
+	if (task_is_dying())
+		goto out;
+
+	/*
 	 * The allocating task should reclaim at least the batch size, but for
 	 * subsequent retries we only want to do what's necessary to prevent oom
 	 * or breaching resource isolation.
@@ -2673,6 +2710,9 @@ retry_reclaim:
 	}
 
 	/*
+	 * Reclaim didn't manage to push usage below the limit, slow
+	 * this allocating task down.
+	 *
 	 * If we exit early, we're guaranteed to die (since
 	 * schedule_timeout_killable sets TASK_KILLABLE). This means we don't
 	 * need to account for any ill-begotten jiffies to pay them off later.
@@ -2867,11 +2907,17 @@ done_restock:
 		}
 	} while ((memcg = parent_mem_cgroup(memcg)));
 
+	/*
+	 * Reclaim is set up above to be called from the userland
+	 * return path. But also attempt synchronous reclaim to avoid
+	 * excessive overrun while the task is still inside the
+	 * kernel. If this is successful, the return path will see it
+	 * when it rechecks the overage and simply bail out.
+	 */
 	if (current->memcg_nr_pages_over_high > MEMCG_CHARGE_BATCH &&
 	    !(current->flags & PF_MEMALLOC) &&
-	    gfpflags_allow_blocking(gfp_mask)) {
+	    gfpflags_allow_blocking(gfp_mask))
 		mem_cgroup_handle_over_high(gfp_mask);
-	}
 	return 0;
 }
 
@@ -4177,7 +4223,7 @@ static int memcg_numa_stat_show(struct seq_file *m, void *v)
 	int nid;
 	struct mem_cgroup *memcg = mem_cgroup_from_seq(m);
 
-	mem_cgroup_flush_stats();
+	mem_cgroup_flush_stats(memcg);
 
 	for (stat = stats; stat < stats + ARRAY_SIZE(stats); stat++) {
 		seq_printf(m, "%s=%lu", stat->name,
@@ -4258,7 +4304,7 @@ static void memcg1_stat_format(struct mem_cgroup *memcg, struct seq_buf *s)
 
 	BUILD_BUG_ON(ARRAY_SIZE(memcg1_stat_names) != ARRAY_SIZE(memcg1_stats));
 
-	mem_cgroup_flush_stats();
+	mem_cgroup_flush_stats(memcg);
 
 	for (i = 0; i < ARRAY_SIZE(memcg1_stats); i++) {
 		unsigned long nr;
@@ -4754,7 +4800,7 @@ void mem_cgroup_wb_stats(struct bdi_writeback *wb, unsigned long *pfilepages,
 	struct mem_cgroup *memcg = mem_cgroup_from_css(wb->memcg_css);
 	struct mem_cgroup *parent;
 
-	mem_cgroup_flush_stats();
+	mem_cgroup_flush_stats(memcg);
 
 	*pdirty = memcg_page_state(memcg, NR_FILE_DIRTY);
 	*pwriteback = memcg_page_state(memcg, NR_WRITEBACK);
@@ -5150,7 +5196,7 @@ out_kfree:
 	return ret;
 }
 
-#if defined(CONFIG_MEMCG_KMEM) && (defined(CONFIG_SLAB) || defined(CONFIG_SLUB_DEBUG))
+#if defined(CONFIG_MEMCG_KMEM) && defined(CONFIG_SLUB_DEBUG)
 static int mem_cgroup_slab_show(struct seq_file *m, void *p)
 {
 	/*
@@ -5259,8 +5305,7 @@ static struct cftype mem_cgroup_legacy_files[] = {
 		.write = mem_cgroup_reset,
 		.read_u64 = mem_cgroup_read_u64,
 	},
-#if defined(CONFIG_MEMCG_KMEM) && \
-	(defined(CONFIG_SLAB) || defined(CONFIG_SLUB_DEBUG))
+#if defined(CONFIG_MEMCG_KMEM) && defined(CONFIG_SLUB_DEBUG)
 	{
 		.name = "kmem.slabinfo",
 		.seq_show = mem_cgroup_slab_show,
@@ -5437,10 +5482,11 @@ static void mem_cgroup_free(struct mem_cgroup *memcg)
 	__mem_cgroup_free(memcg);
 }
 
-static struct mem_cgroup *mem_cgroup_alloc(void)
+static struct mem_cgroup *mem_cgroup_alloc(struct mem_cgroup *parent)
 {
+	struct memcg_vmstats_percpu *statc, *pstatc;
 	struct mem_cgroup *memcg;
-	int node;
+	int node, cpu;
 	int __maybe_unused i;
 	long error = -ENOMEM;
 
@@ -5464,6 +5510,14 @@ static struct mem_cgroup *mem_cgroup_alloc(void)
 	if (!memcg->vmstats_percpu)
 		goto fail;
 
+	for_each_possible_cpu(cpu) {
+		if (parent)
+			pstatc = per_cpu_ptr(parent->vmstats_percpu, cpu);
+		statc = per_cpu_ptr(memcg->vmstats_percpu, cpu);
+		statc->parent = parent ? pstatc : NULL;
+		statc->vmstats = memcg->vmstats;
+	}
+
 	for_each_node(node)
 		if (alloc_mem_cgroup_per_node_info(memcg, node))
 			goto fail;
@@ -5509,7 +5563,7 @@ mem_cgroup_css_alloc(struct cgroup_subsys_state *parent_css)
 	struct mem_cgroup *memcg, *old_memcg;
 
 	old_memcg = set_active_memcg(parent);
-	memcg = mem_cgroup_alloc();
+	memcg = mem_cgroup_alloc(parent);
 	set_active_memcg(old_memcg);
 	if (IS_ERR(memcg))
 		return ERR_CAST(memcg);
@@ -5518,6 +5572,8 @@ mem_cgroup_css_alloc(struct cgroup_subsys_state *parent_css)
 	WRITE_ONCE(memcg->soft_limit, PAGE_COUNTER_MAX);
 #if defined(CONFIG_MEMCG_KMEM) && defined(CONFIG_ZSWAP)
 	memcg->zswap_max = PAGE_COUNTER_MAX;
+	WRITE_ONCE(memcg->zswap_writeback,
+		!parent || READ_ONCE(parent->zswap_writeback));
 #endif
 	page_counter_set_high(&memcg->swap, PAGE_COUNTER_MAX);
 	if (parent) {
@@ -5614,6 +5670,8 @@ static void mem_cgroup_css_offline(struct cgroup_subsys_state *css)
 	page_counter_set_min(&memcg->memory, 0);
 	page_counter_set_low(&memcg->memory, 0);
 
+	zswap_memcg_offline_cleanup(memcg);
+
 	memcg_offline_kmem(memcg);
 	reparent_shrinker_deferred(memcg);
 	wb_memcg_offline(memcg);
@@ -5784,6 +5842,10 @@ static void mem_cgroup_css_rstat_flush(struct cgroup_subsys_state *css, int cpu)
 			}
 		}
 	}
+	statc->stats_updates = 0;
+	/* We are in a per-cpu loop here, only do the atomic write once */
+	if (atomic64_read(&memcg->vmstats->stats_updates))
+		atomic64_set(&memcg->vmstats->stats_updates, 0);
 }
 
 #ifdef CONFIG_MMU
@@ -6783,6 +6845,10 @@ static ssize_t memory_max_write(struct kernfs_open_file *of,
 	return nbytes;
 }
 
+/*
+ * Note: don't forget to update the 'samples/cgroup/memcg_event_listener'
+ * if any new events become available.
+ */
 static void __memory_events_show(struct seq_file *m, atomic_long_t *events)
 {
 	seq_printf(m, "low %lu\n", atomic_long_read(&events[MEMCG_LOW]));
@@ -6839,7 +6905,7 @@ static int memory_numa_stat_show(struct seq_file *m, void *v)
 	int i;
 	struct mem_cgroup *memcg = mem_cgroup_from_seq(m);
 
-	mem_cgroup_flush_stats();
+	mem_cgroup_flush_stats(memcg);
 
 	for (i = 0; i < ARRAY_SIZE(memory_stats); i++) {
 		int nid;
@@ -8085,7 +8151,11 @@ bool obj_cgroup_may_zswap(struct obj_cgroup *objcg)
 			break;
 		}
 
-		cgroup_rstat_flush(memcg->css.cgroup);
+		/*
+		 * mem_cgroup_flush_stats() ignores small changes. Use
+		 * do_flush_stats() directly to get accurate stats for charging.
+		 */
+		do_flush_stats(memcg);
 		pages = memcg_page_state(memcg, MEMCG_ZSWAP_B) / PAGE_SIZE;
 		if (pages < max)
 			continue;
@@ -8147,11 +8217,19 @@ void obj_cgroup_uncharge_zswap(struct obj_cgroup *objcg, size_t size)
 	rcu_read_unlock();
 }
 
+bool mem_cgroup_zswap_writeback_enabled(struct mem_cgroup *memcg)
+{
+	/* if zswap is disabled, do not block pages going to the swapping device */
+	return !is_zswap_enabled() || !memcg || READ_ONCE(memcg->zswap_writeback);
+}
+
 static u64 zswap_current_read(struct cgroup_subsys_state *css,
 			      struct cftype *cft)
 {
-	cgroup_rstat_flush(css->cgroup);
-	return memcg_page_state(mem_cgroup_from_css(css), MEMCG_ZSWAP_B);
+	struct mem_cgroup *memcg = mem_cgroup_from_css(css);
+
+	mem_cgroup_flush_stats(memcg);
+	return memcg_page_state(memcg, MEMCG_ZSWAP_B);
 }
 
 static int zswap_max_show(struct seq_file *m, void *v)
@@ -8177,6 +8255,31 @@ static ssize_t zswap_max_write(struct kernfs_open_file *of,
 	return nbytes;
 }
 
+static int zswap_writeback_show(struct seq_file *m, void *v)
+{
+	struct mem_cgroup *memcg = mem_cgroup_from_seq(m);
+
+	seq_printf(m, "%d\n", READ_ONCE(memcg->zswap_writeback));
+	return 0;
+}
+
+static ssize_t zswap_writeback_write(struct kernfs_open_file *of,
+				char *buf, size_t nbytes, loff_t off)
+{
+	struct mem_cgroup *memcg = mem_cgroup_from_css(of_css(of));
+	int zswap_writeback;
+	ssize_t parse_ret = kstrtoint(strstrip(buf), 0, &zswap_writeback);
+
+	if (parse_ret)
+		return parse_ret;
+
+	if (zswap_writeback != 0 && zswap_writeback != 1)
+		return -EINVAL;
+
+	WRITE_ONCE(memcg->zswap_writeback, zswap_writeback);
+	return nbytes;
+}
+
 static struct cftype zswap_files[] = {
 	{
 		.name = "zswap.current",
@@ -8189,6 +8292,11 @@ static struct cftype zswap_files[] = {
 		.seq_show = zswap_max_show,
 		.write = zswap_max_write,
 	},
+	{
+		.name = "zswap.writeback",
+		.seq_show = zswap_writeback_show,
+		.write = zswap_writeback_write,
+	},
 	{ }	/* terminate */
 };
 #endif /* CONFIG_MEMCG_KMEM && CONFIG_ZSWAP */