[PATCH 1/3] mm: memcontrol: eliminate raw access to stat and event counters

[PATCH 1/3] mm: memcontrol: eliminate raw access to stat and event counters

[Johannes Weiner]

Replace all raw 'this_cpu_' modifications of the stat and event
per-cpu counters with API functions such as mod_memcg_state().

This makes the code easier to read, but is also in preparation for the
next patch, which changes the per-cpu implementation of those counters.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
---
 include/linux/memcontrol.h | 31 +++++++++++++++---------
 mm/memcontrol.c            | 59 ++++++++++++++++++++--------------------------
 2 files changed, 45 insertions(+), 45 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 69966c461d1c..2c80b69dd266 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -272,13 +272,6 @@ static inline bool mem_cgroup_disabled(void)
 	return !cgroup_subsys_enabled(memory_cgrp_subsys);
 }
 
-static inline void mem_cgroup_event(struct mem_cgroup *memcg,
-				    enum memcg_event_item event)
-{
-	this_cpu_inc(memcg->stat->events[event]);
-	cgroup_file_notify(&memcg->events_file);
-}
-
 bool mem_cgroup_low(struct mem_cgroup *root, struct mem_cgroup *memcg);
 
 int mem_cgroup_try_charge(struct page *page, struct mm_struct *mm,
@@ -627,15 +620,23 @@ unsigned long mem_cgroup_soft_limit_reclaim(pg_data_t *pgdat, int order,
 						gfp_t gfp_mask,
 						unsigned long *total_scanned);
 
+/* idx can be of type enum memcg_event_item or vm_event_item */
+static inline void __count_memcg_events(struct mem_cgroup *memcg,
+					int idx, unsigned long count)
+{
+	if (!mem_cgroup_disabled())
+		__this_cpu_add(memcg->stat->events[idx], count);
+}
+
+/* idx can be of type enum memcg_event_item or vm_event_item */
 static inline void count_memcg_events(struct mem_cgroup *memcg,
-				      enum vm_event_item idx,
-				      unsigned long count)
+				      int idx, unsigned long count)
 {
 	if (!mem_cgroup_disabled())
 		this_cpu_add(memcg->stat->events[idx], count);
 }
 
-/* idx can be of type enum memcg_stat_item or node_stat_item */
+/* idx can be of type enum memcg_event_item or vm_event_item */
 static inline void count_memcg_page_event(struct page *page,
 					  int idx)
 {
@@ -654,12 +655,20 @@ static inline void count_memcg_event_mm(struct mm_struct *mm,
 	rcu_read_lock();
 	memcg = mem_cgroup_from_task(rcu_dereference(mm->owner));
 	if (likely(memcg)) {
-		this_cpu_inc(memcg->stat->events[idx]);
+		count_memcg_events(memcg, idx, 1);
 		if (idx == OOM_KILL)
 			cgroup_file_notify(&memcg->events_file);
 	}
 	rcu_read_unlock();
 }
+
+static inline void mem_cgroup_event(struct mem_cgroup *memcg,
+				    enum memcg_event_item event)
+{
+	count_memcg_events(memcg, event, 1);
+	cgroup_file_notify(&memcg->events_file);
+}
+
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 void mem_cgroup_split_huge_fixup(struct page *head);
 #endif
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 50e6906314f8..dabbc076e503 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -586,23 +586,23 @@ static void mem_cgroup_charge_statistics(struct mem_cgroup *memcg,
 	 * counted as CACHE even if it's on ANON LRU.
 	 */
 	if (PageAnon(page))
-		__this_cpu_add(memcg->stat->count[MEMCG_RSS], nr_pages);
+		__mod_memcg_state(memcg, MEMCG_RSS, nr_pages);
 	else {
-		__this_cpu_add(memcg->stat->count[MEMCG_CACHE], nr_pages);
+		__mod_memcg_state(memcg, MEMCG_CACHE, nr_pages);
 		if (PageSwapBacked(page))
-			__this_cpu_add(memcg->stat->count[NR_SHMEM], nr_pages);
+			__mod_memcg_state(memcg, NR_SHMEM, nr_pages);
 	}
 
 	if (compound) {
 		VM_BUG_ON_PAGE(!PageTransHuge(page), page);
-		__this_cpu_add(memcg->stat->count[MEMCG_RSS_HUGE], nr_pages);
+		__mod_memcg_state(memcg, MEMCG_RSS_HUGE, nr_pages);
 	}
 
 	/* pagein of a big page is an event. So, ignore page size */
 	if (nr_pages > 0)
-		__this_cpu_inc(memcg->stat->events[PGPGIN]);
+		__count_memcg_events(memcg, PGPGIN, 1);
 	else {
-		__this_cpu_inc(memcg->stat->events[PGPGOUT]);
+		__count_memcg_events(memcg, PGPGOUT, 1);
 		nr_pages = -nr_pages; /* for event */
 	}
 
@@ -2415,18 +2415,11 @@ void mem_cgroup_split_huge_fixup(struct page *head)
 	for (i = 1; i < HPAGE_PMD_NR; i++)
 		head[i].mem_cgroup = head->mem_cgroup;
 
-	__this_cpu_sub(head->mem_cgroup->stat->count[MEMCG_RSS_HUGE],
-		       HPAGE_PMD_NR);
+	__mod_memcg_state(head->mem_cgroup, MEMCG_RSS_HUGE, -HPAGE_PMD_NR);
 }
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
 
 #ifdef CONFIG_MEMCG_SWAP
-static void mem_cgroup_swap_statistics(struct mem_cgroup *memcg,
-				       int nr_entries)
-{
-	this_cpu_add(memcg->stat->count[MEMCG_SWAP], nr_entries);
-}
-
 /**
  * mem_cgroup_move_swap_account - move swap charge and swap_cgroup's record.
  * @entry: swap entry to be moved
@@ -2450,8 +2443,8 @@ static int mem_cgroup_move_swap_account(swp_entry_t entry,
 	new_id = mem_cgroup_id(to);
 
 	if (swap_cgroup_cmpxchg(entry, old_id, new_id) == old_id) {
-		mem_cgroup_swap_statistics(from, -1);
-		mem_cgroup_swap_statistics(to, 1);
+		mod_memcg_state(from, MEMCG_SWAP, -1);
+		mod_memcg_state(to, MEMCG_SWAP, 1);
 		return 0;
 	}
 	return -EINVAL;
@@ -4584,8 +4577,8 @@ static int mem_cgroup_move_account(struct page *page,
 	spin_lock_irqsave(&from->move_lock, flags);
 
 	if (!anon && page_mapped(page)) {
-		__this_cpu_sub(from->stat->count[NR_FILE_MAPPED], nr_pages);
-		__this_cpu_add(to->stat->count[NR_FILE_MAPPED], nr_pages);
+		__mod_memcg_state(from, NR_FILE_MAPPED, -nr_pages);
+		__mod_memcg_state(to, NR_FILE_MAPPED, nr_pages);
 	}
 
 	/*
@@ -4597,16 +4590,14 @@ static int mem_cgroup_move_account(struct page *page,
 		struct address_space *mapping = page_mapping(page);
 
 		if (mapping_cap_account_dirty(mapping)) {
-			__this_cpu_sub(from->stat->count[NR_FILE_DIRTY],
-				       nr_pages);
-			__this_cpu_add(to->stat->count[NR_FILE_DIRTY],
-				       nr_pages);
+			__mod_memcg_state(from, NR_FILE_DIRTY, -nr_pages);
+			__mod_memcg_state(to, NR_FILE_DIRTY, nr_pages);
 		}
 	}
 
 	if (PageWriteback(page)) {
-		__this_cpu_sub(from->stat->count[NR_WRITEBACK], nr_pages);
-		__this_cpu_add(to->stat->count[NR_WRITEBACK], nr_pages);
+		__mod_memcg_state(from, NR_WRITEBACK, -nr_pages);
+		__mod_memcg_state(to, NR_WRITEBACK, nr_pages);
 	}
 
 	/*
@@ -5642,11 +5633,11 @@ static void uncharge_batch(const struct uncharge_gather *ug)
 	}
 
 	local_irq_save(flags);
-	__this_cpu_sub(ug->memcg->stat->count[MEMCG_RSS], ug->nr_anon);
-	__this_cpu_sub(ug->memcg->stat->count[MEMCG_CACHE], ug->nr_file);
-	__this_cpu_sub(ug->memcg->stat->count[MEMCG_RSS_HUGE], ug->nr_huge);
-	__this_cpu_sub(ug->memcg->stat->count[NR_SHMEM], ug->nr_shmem);
-	__this_cpu_add(ug->memcg->stat->events[PGPGOUT], ug->pgpgout);
+	__mod_memcg_state(ug->memcg, MEMCG_RSS, -ug->nr_anon);
+	__mod_memcg_state(ug->memcg, MEMCG_CACHE, -ug->nr_file);
+	__mod_memcg_state(ug->memcg, MEMCG_RSS_HUGE, -ug->nr_huge);
+	__mod_memcg_state(ug->memcg, NR_SHMEM, -ug->nr_shmem);
+	__count_memcg_events(ug->memcg, PGPGOUT, ug->pgpgout);
 	__this_cpu_add(ug->memcg->stat->nr_page_events, nr_pages);
 	memcg_check_events(ug->memcg, ug->dummy_page);
 	local_irq_restore(flags);
@@ -5874,7 +5865,7 @@ bool mem_cgroup_charge_skmem(struct mem_cgroup *memcg, unsigned int nr_pages)
 	if (in_softirq())
 		gfp_mask = GFP_NOWAIT;
 
-	this_cpu_add(memcg->stat->count[MEMCG_SOCK], nr_pages);
+	mod_memcg_state(memcg, MEMCG_SOCK, nr_pages);
 
 	if (try_charge(memcg, gfp_mask, nr_pages) == 0)
 		return true;
@@ -5895,7 +5886,7 @@ void mem_cgroup_uncharge_skmem(struct mem_cgroup *memcg, unsigned int nr_pages)
 		return;
 	}
 
-	this_cpu_sub(memcg->stat->count[MEMCG_SOCK], nr_pages);
+	mod_memcg_state(memcg, MEMCG_SOCK, -nr_pages);
 
 	refill_stock(memcg, nr_pages);
 }
@@ -6019,7 +6010,7 @@ void mem_cgroup_swapout(struct page *page, swp_entry_t entry)
 	oldid = swap_cgroup_record(entry, mem_cgroup_id(swap_memcg),
 				   nr_entries);
 	VM_BUG_ON_PAGE(oldid, page);
-	mem_cgroup_swap_statistics(swap_memcg, nr_entries);
+	mod_memcg_state(swap_memcg, MEMCG_SWAP, nr_entries);
 
 	page->mem_cgroup = NULL;
 
@@ -6085,7 +6076,7 @@ int mem_cgroup_try_charge_swap(struct page *page, swp_entry_t entry)
 		mem_cgroup_id_get_many(memcg, nr_pages - 1);
 	oldid = swap_cgroup_record(entry, mem_cgroup_id(memcg), nr_pages);
 	VM_BUG_ON_PAGE(oldid, page);
-	mem_cgroup_swap_statistics(memcg, nr_pages);
+	mod_memcg_state(memcg, MEMCG_SWAP, nr_pages);
 
 	return 0;
 }
@@ -6113,7 +6104,7 @@ void mem_cgroup_uncharge_swap(swp_entry_t entry, unsigned int nr_pages)
 			else
 				page_counter_uncharge(&memcg->memsw, nr_pages);
 		}
-		mem_cgroup_swap_statistics(memcg, -nr_pages);
+		mod_memcg_state(memcg, MEMCG_SWAP, -nr_pages);
 		mem_cgroup_id_put_many(memcg, nr_pages);
 	}
 	rcu_read_unlock();
-- 
2.15.0

[PATCH 1/3] mm: memcontrol: eliminate raw access to stat and event counters

[Johannes Weiner]

Replace all raw 'this_cpu_' modifications of the stat and event
per-cpu counters with API functions such as mod_memcg_state().

This makes the code easier to read, but is also in preparation for the
next patch, which changes the per-cpu implementation of those counters.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
---
 include/linux/memcontrol.h | 31 +++++++++++++++---------
 mm/memcontrol.c            | 59 ++++++++++++++++++++--------------------------
 2 files changed, 45 insertions(+), 45 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 69966c461d1c..2c80b69dd266 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -272,13 +272,6 @@ static inline bool mem_cgroup_disabled(void)
 	return !cgroup_subsys_enabled(memory_cgrp_subsys);
 }
 
-static inline void mem_cgroup_event(struct mem_cgroup *memcg,
-				    enum memcg_event_item event)
-{
-	this_cpu_inc(memcg->stat->events[event]);
-	cgroup_file_notify(&memcg->events_file);
-}
-
 bool mem_cgroup_low(struct mem_cgroup *root, struct mem_cgroup *memcg);
 
 int mem_cgroup_try_charge(struct page *page, struct mm_struct *mm,
@@ -627,15 +620,23 @@ unsigned long mem_cgroup_soft_limit_reclaim(pg_data_t *pgdat, int order,
 						gfp_t gfp_mask,
 						unsigned long *total_scanned);
 
+/* idx can be of type enum memcg_event_item or vm_event_item */
+static inline void __count_memcg_events(struct mem_cgroup *memcg,
+					int idx, unsigned long count)
+{
+	if (!mem_cgroup_disabled())
+		__this_cpu_add(memcg->stat->events[idx], count);
+}
+
+/* idx can be of type enum memcg_event_item or vm_event_item */
 static inline void count_memcg_events(struct mem_cgroup *memcg,
-				      enum vm_event_item idx,
-				      unsigned long count)
+				      int idx, unsigned long count)
 {
 	if (!mem_cgroup_disabled())
 		this_cpu_add(memcg->stat->events[idx], count);
 }
 
-/* idx can be of type enum memcg_stat_item or node_stat_item */
+/* idx can be of type enum memcg_event_item or vm_event_item */
 static inline void count_memcg_page_event(struct page *page,
 					  int idx)
 {
@@ -654,12 +655,20 @@ static inline void count_memcg_event_mm(struct mm_struct *mm,
 	rcu_read_lock();
 	memcg = mem_cgroup_from_task(rcu_dereference(mm->owner));
 	if (likely(memcg)) {
-		this_cpu_inc(memcg->stat->events[idx]);
+		count_memcg_events(memcg, idx, 1);
 		if (idx == OOM_KILL)
 			cgroup_file_notify(&memcg->events_file);
 	}
 	rcu_read_unlock();
 }
+
+static inline void mem_cgroup_event(struct mem_cgroup *memcg,
+				    enum memcg_event_item event)
+{
+	count_memcg_events(memcg, event, 1);
+	cgroup_file_notify(&memcg->events_file);
+}
+
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 void mem_cgroup_split_huge_fixup(struct page *head);
 #endif
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 50e6906314f8..dabbc076e503 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -586,23 +586,23 @@ static void mem_cgroup_charge_statistics(struct mem_cgroup *memcg,
 	 * counted as CACHE even if it's on ANON LRU.
 	 */
 	if (PageAnon(page))
-		__this_cpu_add(memcg->stat->count[MEMCG_RSS], nr_pages);
+		__mod_memcg_state(memcg, MEMCG_RSS, nr_pages);
 	else {
-		__this_cpu_add(memcg->stat->count[MEMCG_CACHE], nr_pages);
+		__mod_memcg_state(memcg, MEMCG_CACHE, nr_pages);
 		if (PageSwapBacked(page))
-			__this_cpu_add(memcg->stat->count[NR_SHMEM], nr_pages);
+			__mod_memcg_state(memcg, NR_SHMEM, nr_pages);
 	}
 
 	if (compound) {
 		VM_BUG_ON_PAGE(!PageTransHuge(page), page);
-		__this_cpu_add(memcg->stat->count[MEMCG_RSS_HUGE], nr_pages);
+		__mod_memcg_state(memcg, MEMCG_RSS_HUGE, nr_pages);
 	}
 
 	/* pagein of a big page is an event. So, ignore page size */
 	if (nr_pages > 0)
-		__this_cpu_inc(memcg->stat->events[PGPGIN]);
+		__count_memcg_events(memcg, PGPGIN, 1);
 	else {
-		__this_cpu_inc(memcg->stat->events[PGPGOUT]);
+		__count_memcg_events(memcg, PGPGOUT, 1);
 		nr_pages = -nr_pages; /* for event */
 	}
 
@@ -2415,18 +2415,11 @@ void mem_cgroup_split_huge_fixup(struct page *head)
 	for (i = 1; i < HPAGE_PMD_NR; i++)
 		head[i].mem_cgroup = head->mem_cgroup;
 
-	__this_cpu_sub(head->mem_cgroup->stat->count[MEMCG_RSS_HUGE],
-		       HPAGE_PMD_NR);
+	__mod_memcg_state(head->mem_cgroup, MEMCG_RSS_HUGE, -HPAGE_PMD_NR);
 }
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
 
 #ifdef CONFIG_MEMCG_SWAP
-static void mem_cgroup_swap_statistics(struct mem_cgroup *memcg,
-				       int nr_entries)
-{
-	this_cpu_add(memcg->stat->count[MEMCG_SWAP], nr_entries);
-}
-
 /**
  * mem_cgroup_move_swap_account - move swap charge and swap_cgroup's record.
  * @entry: swap entry to be moved
@@ -2450,8 +2443,8 @@ static int mem_cgroup_move_swap_account(swp_entry_t entry,
 	new_id = mem_cgroup_id(to);
 
 	if (swap_cgroup_cmpxchg(entry, old_id, new_id) == old_id) {
-		mem_cgroup_swap_statistics(from, -1);
-		mem_cgroup_swap_statistics(to, 1);
+		mod_memcg_state(from, MEMCG_SWAP, -1);
+		mod_memcg_state(to, MEMCG_SWAP, 1);
 		return 0;
 	}
 	return -EINVAL;
@@ -4584,8 +4577,8 @@ static int mem_cgroup_move_account(struct page *page,
 	spin_lock_irqsave(&from->move_lock, flags);
 
 	if (!anon && page_mapped(page)) {
-		__this_cpu_sub(from->stat->count[NR_FILE_MAPPED], nr_pages);
-		__this_cpu_add(to->stat->count[NR_FILE_MAPPED], nr_pages);
+		__mod_memcg_state(from, NR_FILE_MAPPED, -nr_pages);
+		__mod_memcg_state(to, NR_FILE_MAPPED, nr_pages);
 	}
 
 	/*
@@ -4597,16 +4590,14 @@ static int mem_cgroup_move_account(struct page *page,
 		struct address_space *mapping = page_mapping(page);
 
 		if (mapping_cap_account_dirty(mapping)) {
-			__this_cpu_sub(from->stat->count[NR_FILE_DIRTY],
-				       nr_pages);
-			__this_cpu_add(to->stat->count[NR_FILE_DIRTY],
-				       nr_pages);
+			__mod_memcg_state(from, NR_FILE_DIRTY, -nr_pages);
+			__mod_memcg_state(to, NR_FILE_DIRTY, nr_pages);
 		}
 	}
 
 	if (PageWriteback(page)) {
-		__this_cpu_sub(from->stat->count[NR_WRITEBACK], nr_pages);
-		__this_cpu_add(to->stat->count[NR_WRITEBACK], nr_pages);
+		__mod_memcg_state(from, NR_WRITEBACK, -nr_pages);
+		__mod_memcg_state(to, NR_WRITEBACK, nr_pages);
 	}
 
 	/*
@@ -5642,11 +5633,11 @@ static void uncharge_batch(const struct uncharge_gather *ug)
 	}
 
 	local_irq_save(flags);
-	__this_cpu_sub(ug->memcg->stat->count[MEMCG_RSS], ug->nr_anon);
-	__this_cpu_sub(ug->memcg->stat->count[MEMCG_CACHE], ug->nr_file);
-	__this_cpu_sub(ug->memcg->stat->count[MEMCG_RSS_HUGE], ug->nr_huge);
-	__this_cpu_sub(ug->memcg->stat->count[NR_SHMEM], ug->nr_shmem);
-	__this_cpu_add(ug->memcg->stat->events[PGPGOUT], ug->pgpgout);
+	__mod_memcg_state(ug->memcg, MEMCG_RSS, -ug->nr_anon);
+	__mod_memcg_state(ug->memcg, MEMCG_CACHE, -ug->nr_file);
+	__mod_memcg_state(ug->memcg, MEMCG_RSS_HUGE, -ug->nr_huge);
+	__mod_memcg_state(ug->memcg, NR_SHMEM, -ug->nr_shmem);
+	__count_memcg_events(ug->memcg, PGPGOUT, ug->pgpgout);
 	__this_cpu_add(ug->memcg->stat->nr_page_events, nr_pages);
 	memcg_check_events(ug->memcg, ug->dummy_page);
 	local_irq_restore(flags);
@@ -5874,7 +5865,7 @@ bool mem_cgroup_charge_skmem(struct mem_cgroup *memcg, unsigned int nr_pages)
 	if (in_softirq())
 		gfp_mask = GFP_NOWAIT;
 
-	this_cpu_add(memcg->stat->count[MEMCG_SOCK], nr_pages);
+	mod_memcg_state(memcg, MEMCG_SOCK, nr_pages);
 
 	if (try_charge(memcg, gfp_mask, nr_pages) == 0)
 		return true;
@@ -5895,7 +5886,7 @@ void mem_cgroup_uncharge_skmem(struct mem_cgroup *memcg, unsigned int nr_pages)
 		return;
 	}
 
-	this_cpu_sub(memcg->stat->count[MEMCG_SOCK], nr_pages);
+	mod_memcg_state(memcg, MEMCG_SOCK, -nr_pages);
 
 	refill_stock(memcg, nr_pages);
 }
@@ -6019,7 +6010,7 @@ void mem_cgroup_swapout(struct page *page, swp_entry_t entry)
 	oldid = swap_cgroup_record(entry, mem_cgroup_id(swap_memcg),
 				   nr_entries);
 	VM_BUG_ON_PAGE(oldid, page);
-	mem_cgroup_swap_statistics(swap_memcg, nr_entries);
+	mod_memcg_state(swap_memcg, MEMCG_SWAP, nr_entries);
 
 	page->mem_cgroup = NULL;
 
@@ -6085,7 +6076,7 @@ int mem_cgroup_try_charge_swap(struct page *page, swp_entry_t entry)
 		mem_cgroup_id_get_many(memcg, nr_pages - 1);
 	oldid = swap_cgroup_record(entry, mem_cgroup_id(memcg), nr_pages);
 	VM_BUG_ON_PAGE(oldid, page);
-	mem_cgroup_swap_statistics(memcg, nr_pages);
+	mod_memcg_state(memcg, MEMCG_SWAP, nr_pages);
 
 	return 0;
 }
@@ -6113,7 +6104,7 @@ void mem_cgroup_uncharge_swap(swp_entry_t entry, unsigned int nr_pages)
 			else
 				page_counter_uncharge(&memcg->memsw, nr_pages);
 		}
-		mem_cgroup_swap_statistics(memcg, -nr_pages);
+		mod_memcg_state(memcg, MEMCG_SWAP, -nr_pages);
 		mem_cgroup_id_put_many(memcg, nr_pages);
 	}
 	rcu_read_unlock();
-- 
2.15.0

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[PATCH 2/3] mm: memcontrol: implement lruvec stat functions on top of each other

[Johannes Weiner]

The implementation of the lruvec stat functions and their variants for
accounting through a page, or accounting from a preemptible context,
are mostly identical and needlessly repetitive.

Implement the lruvec_page functions by looking up the page's lruvec
and then using the lruvec function.

Implement the functions for preemptible contexts by disabling
preemption before calling the atomic context functions.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
---
 include/linux/memcontrol.h | 44 ++++++++++++++++++++++----------------------
 1 file changed, 22 insertions(+), 22 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 2c80b69dd266..1ffc54ac4cc9 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -569,51 +569,51 @@ static inline void __mod_lruvec_state(struct lruvec *lruvec,
 {
 	struct mem_cgroup_per_node *pn;
 
+	/* Update node */
 	__mod_node_page_state(lruvec_pgdat(lruvec), idx, val);
+
 	if (mem_cgroup_disabled())
 		return;
+
 	pn = container_of(lruvec, struct mem_cgroup_per_node, lruvec);
+
+	/* Update memcg */
 	__mod_memcg_state(pn->memcg, idx, val);
+
+	/* Update lruvec */
 	__this_cpu_add(pn->lruvec_stat->count[idx], val);
 }
 
 static inline void mod_lruvec_state(struct lruvec *lruvec,
 				    enum node_stat_item idx, int val)
 {
-	struct mem_cgroup_per_node *pn;
-
-	mod_node_page_state(lruvec_pgdat(lruvec), idx, val);
-	if (mem_cgroup_disabled())
-		return;
-	pn = container_of(lruvec, struct mem_cgroup_per_node, lruvec);
-	mod_memcg_state(pn->memcg, idx, val);
-	this_cpu_add(pn->lruvec_stat->count[idx], val);
+	preempt_disable();
+	__mod_lruvec_state(lruvec, idx, val);
+	preempt_enable();
 }
 
 static inline void __mod_lruvec_page_state(struct page *page,
 					   enum node_stat_item idx, int val)
 {
-	struct mem_cgroup_per_node *pn;
+	pg_data_t *pgdat = page_pgdat(page);
+	struct lruvec *lruvec;
 
-	__mod_node_page_state(page_pgdat(page), idx, val);
-	if (mem_cgroup_disabled() || !page->mem_cgroup)
+	/* Untracked pages have no memcg, no lruvec. Update only the node */
+	if (!page->mem_cgroup) {
+		__mod_node_page_state(pgdat, idx, val);
 		return;
-	__mod_memcg_state(page->mem_cgroup, idx, val);
-	pn = page->mem_cgroup->nodeinfo[page_to_nid(page)];
-	__this_cpu_add(pn->lruvec_stat->count[idx], val);
+	}
+
+	lruvec = mem_cgroup_lruvec(pgdat, page->mem_cgroup);
+	__mod_lruvec_state(lruvec, idx, val);
 }
 
 static inline void mod_lruvec_page_state(struct page *page,
 					 enum node_stat_item idx, int val)
 {
-	struct mem_cgroup_per_node *pn;
-
-	mod_node_page_state(page_pgdat(page), idx, val);
-	if (mem_cgroup_disabled() || !page->mem_cgroup)
-		return;
-	mod_memcg_state(page->mem_cgroup, idx, val);
-	pn = page->mem_cgroup->nodeinfo[page_to_nid(page)];
-	this_cpu_add(pn->lruvec_stat->count[idx], val);
+	preempt_disable();
+	__mod_lruvec_page_state(page, idx, val);
+	preempt_enable();
 }
 
 unsigned long mem_cgroup_soft_limit_reclaim(pg_data_t *pgdat, int order,
-- 
2.15.0

[PATCH 2/3] mm: memcontrol: implement lruvec stat functions on top of each other

[Johannes Weiner]

The implementation of the lruvec stat functions and their variants for
accounting through a page, or accounting from a preemptible context,
are mostly identical and needlessly repetitive.

Implement the lruvec_page functions by looking up the page's lruvec
and then using the lruvec function.

Implement the functions for preemptible contexts by disabling
preemption before calling the atomic context functions.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
---
 include/linux/memcontrol.h | 44 ++++++++++++++++++++++----------------------
 1 file changed, 22 insertions(+), 22 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 2c80b69dd266..1ffc54ac4cc9 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -569,51 +569,51 @@ static inline void __mod_lruvec_state(struct lruvec *lruvec,
 {
 	struct mem_cgroup_per_node *pn;
 
+	/* Update node */
 	__mod_node_page_state(lruvec_pgdat(lruvec), idx, val);
+
 	if (mem_cgroup_disabled())
 		return;
+
 	pn = container_of(lruvec, struct mem_cgroup_per_node, lruvec);
+
+	/* Update memcg */
 	__mod_memcg_state(pn->memcg, idx, val);
+
+	/* Update lruvec */
 	__this_cpu_add(pn->lruvec_stat->count[idx], val);
 }
 
 static inline void mod_lruvec_state(struct lruvec *lruvec,
 				    enum node_stat_item idx, int val)
 {
-	struct mem_cgroup_per_node *pn;
-
-	mod_node_page_state(lruvec_pgdat(lruvec), idx, val);
-	if (mem_cgroup_disabled())
-		return;
-	pn = container_of(lruvec, struct mem_cgroup_per_node, lruvec);
-	mod_memcg_state(pn->memcg, idx, val);
-	this_cpu_add(pn->lruvec_stat->count[idx], val);
+	preempt_disable();
+	__mod_lruvec_state(lruvec, idx, val);
+	preempt_enable();
 }
 
 static inline void __mod_lruvec_page_state(struct page *page,
 					   enum node_stat_item idx, int val)
 {
-	struct mem_cgroup_per_node *pn;
+	pg_data_t *pgdat = page_pgdat(page);
+	struct lruvec *lruvec;
 
-	__mod_node_page_state(page_pgdat(page), idx, val);
-	if (mem_cgroup_disabled() || !page->mem_cgroup)
+	/* Untracked pages have no memcg, no lruvec. Update only the node */
+	if (!page->mem_cgroup) {
+		__mod_node_page_state(pgdat, idx, val);
 		return;
-	__mod_memcg_state(page->mem_cgroup, idx, val);
-	pn = page->mem_cgroup->nodeinfo[page_to_nid(page)];
-	__this_cpu_add(pn->lruvec_stat->count[idx], val);
+	}
+
+	lruvec = mem_cgroup_lruvec(pgdat, page->mem_cgroup);
+	__mod_lruvec_state(lruvec, idx, val);
 }
 
 static inline void mod_lruvec_page_state(struct page *page,
 					 enum node_stat_item idx, int val)
 {
-	struct mem_cgroup_per_node *pn;
-
-	mod_node_page_state(page_pgdat(page), idx, val);
-	if (mem_cgroup_disabled() || !page->mem_cgroup)
-		return;
-	mod_memcg_state(page->mem_cgroup, idx, val);
-	pn = page->mem_cgroup->nodeinfo[page_to_nid(page)];
-	this_cpu_add(pn->lruvec_stat->count[idx], val);
+	preempt_disable();
+	__mod_lruvec_page_state(page, idx, val);
+	preempt_enable();
 }
 
 unsigned long mem_cgroup_soft_limit_reclaim(pg_data_t *pgdat, int order,
-- 
2.15.0

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[PATCH 3/3] mm: memcontrol: fix excessive complexity in memory.stat reporting

[Johannes Weiner]

We've seen memory.stat reads in top-level cgroups take up to fourteen
seconds during a userspace bug that created tens of thousands of ghost
cgroups pinned by lingering page cache.

Even with a more reasonable number of cgroups, aggregating memory.stat
is unnecessarily heavy. The complexity is this:

	nr_cgroups * nr_stat_items * nr_possible_cpus

where the stat items are ~70 at this point. With 128 cgroups and 128
CPUs - decent, not enormous setups - reading the top-level memory.stat
has to aggregate over a million per-cpu counters. This doesn't scale.

Instead of spreading the source of truth across all CPUs, use the
per-cpu counters merely to batch updates to shared atomic counters.

This is the same as the per-cpu stocks we use for charging memory to
the shared atomic page_counters, and also the way the global vmstat
counters are implemented.

Vmstat has elaborate spilling thresholds that depend on the number of
CPUs, amount of memory, and memory pressure - carefully balancing the
cost of counter updates with the amount of per-cpu error. That's
because the vmstat counters are system-wide, but also used for
decisions inside the kernel (e.g. NR_FREE_PAGES in the
allocator). Neither is true for the memory controller.

Use the same static batch size we already use for page_counter updates
during charging. The per-cpu error in the stats will be 128k, which is
an acceptable ratio of cores to memory accounting granularity.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
---
 include/linux/memcontrol.h |  96 +++++++++++++++++++++++++++---------------
 mm/memcontrol.c            | 101 +++++++++++++++++++++++----------------------
 2 files changed, 113 insertions(+), 84 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 1ffc54ac4cc9..882046863581 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -108,7 +108,10 @@ struct lruvec_stat {
  */
 struct mem_cgroup_per_node {
 	struct lruvec		lruvec;
-	struct lruvec_stat __percpu *lruvec_stat;
+
+	struct lruvec_stat __percpu *lruvec_stat_cpu;
+	atomic_long_t		lruvec_stat[NR_VM_NODE_STAT_ITEMS];
+
 	unsigned long		lru_zone_size[MAX_NR_ZONES][NR_LRU_LISTS];
 
 	struct mem_cgroup_reclaim_iter	iter[DEF_PRIORITY + 1];
@@ -227,10 +230,10 @@ struct mem_cgroup {
 	spinlock_t		move_lock;
 	struct task_struct	*move_lock_task;
 	unsigned long		move_lock_flags;
-	/*
-	 * percpu counter.
-	 */
-	struct mem_cgroup_stat_cpu __percpu *stat;
+
+	struct mem_cgroup_stat_cpu __percpu *stat_cpu;
+	atomic_long_t		stat[MEMCG_NR_STAT];
+	atomic_long_t		events[MEMCG_NR_EVENTS];
 
 	unsigned long		socket_pressure;
 
@@ -265,6 +268,12 @@ struct mem_cgroup {
 	/* WARNING: nodeinfo must be the last member here */
 };
 
+/*
+ * size of first charge trial. "32" comes from vmscan.c's magic value.
+ * TODO: maybe necessary to use big numbers in big irons.
+ */
+#define MEMCG_CHARGE_BATCH 32U
+
 extern struct mem_cgroup *root_mem_cgroup;
 
 static inline bool mem_cgroup_disabled(void)
@@ -485,32 +494,38 @@ void unlock_page_memcg(struct page *page);
 static inline unsigned long memcg_page_state(struct mem_cgroup *memcg,
 					     int idx)
 {
-	long val = 0;
-	int cpu;
-
-	for_each_possible_cpu(cpu)
-		val += per_cpu(memcg->stat->count[idx], cpu);
-
-	if (val < 0)
-		val = 0;
-
-	return val;
+	long x = atomic_long_read(&memcg->stat[idx]);
+#ifdef CONFIG_SMP
+	if (x < 0)
+		x = 0;
+#endif
+	return x;
 }
 
 /* idx can be of type enum memcg_stat_item or node_stat_item */
 static inline void __mod_memcg_state(struct mem_cgroup *memcg,
 				     int idx, int val)
 {
-	if (!mem_cgroup_disabled())
-		__this_cpu_add(memcg->stat->count[idx], val);
+	long x;
+
+	if (mem_cgroup_disabled())
+		return;
+
+	x = val + __this_cpu_read(memcg->stat_cpu->count[idx]);
+	if (unlikely(abs(x) > MEMCG_CHARGE_BATCH)) {
+		atomic_long_add(x, &memcg->stat[idx]);
+		x = 0;
+	}
+	__this_cpu_write(memcg->stat_cpu->count[idx], x);
 }
 
 /* idx can be of type enum memcg_stat_item or node_stat_item */
 static inline void mod_memcg_state(struct mem_cgroup *memcg,
 				   int idx, int val)
 {
-	if (!mem_cgroup_disabled())
-		this_cpu_add(memcg->stat->count[idx], val);
+	preempt_disable();
+	__mod_memcg_state(memcg, idx, val);
+	preempt_enable();
 }
 
 /**
@@ -548,26 +563,25 @@ static inline unsigned long lruvec_page_state(struct lruvec *lruvec,
 					      enum node_stat_item idx)
 {
 	struct mem_cgroup_per_node *pn;
-	long val = 0;
-	int cpu;
+	long x;
 
 	if (mem_cgroup_disabled())
 		return node_page_state(lruvec_pgdat(lruvec), idx);
 
 	pn = container_of(lruvec, struct mem_cgroup_per_node, lruvec);
-	for_each_possible_cpu(cpu)
-		val += per_cpu(pn->lruvec_stat->count[idx], cpu);
-
-	if (val < 0)
-		val = 0;
-
-	return val;
+	x = atomic_long_read(&pn->lruvec_stat[idx]);
+#ifdef CONFIG_SMP
+	if (x < 0)
+		x = 0;
+#endif
+	return x;
 }
 
 static inline void __mod_lruvec_state(struct lruvec *lruvec,
 				      enum node_stat_item idx, int val)
 {
 	struct mem_cgroup_per_node *pn;
+	long x;
 
 	/* Update node */
 	__mod_node_page_state(lruvec_pgdat(lruvec), idx, val);
@@ -581,7 +595,12 @@ static inline void __mod_lruvec_state(struct lruvec *lruvec,
 	__mod_memcg_state(pn->memcg, idx, val);
 
 	/* Update lruvec */
-	__this_cpu_add(pn->lruvec_stat->count[idx], val);
+	x = val + __this_cpu_read(pn->lruvec_stat_cpu->count[idx]);
+	if (unlikely(abs(x) > MEMCG_CHARGE_BATCH)) {
+		atomic_long_add(x, &pn->lruvec_stat[idx]);
+		x = 0;
+	}
+	__this_cpu_write(pn->lruvec_stat_cpu->count[idx], x);
 }
 
 static inline void mod_lruvec_state(struct lruvec *lruvec,
@@ -624,16 +643,25 @@ unsigned long mem_cgroup_soft_limit_reclaim(pg_data_t *pgdat, int order,
 static inline void __count_memcg_events(struct mem_cgroup *memcg,
 					int idx, unsigned long count)
 {
-	if (!mem_cgroup_disabled())
-		__this_cpu_add(memcg->stat->events[idx], count);
+	unsigned long x;
+
+	if (mem_cgroup_disabled())
+		return;
+
+	x = count + __this_cpu_read(memcg->stat_cpu->events[idx]);
+	if (unlikely(x > MEMCG_CHARGE_BATCH)) {
+		atomic_long_add(x, &memcg->events[idx]);
+		x = 0;
+	}
+	__this_cpu_write(memcg->stat_cpu->events[idx], x);
 }
 
-/* idx can be of type enum memcg_event_item or vm_event_item */
 static inline void count_memcg_events(struct mem_cgroup *memcg,
 				      int idx, unsigned long count)
 {
-	if (!mem_cgroup_disabled())
-		this_cpu_add(memcg->stat->events[idx], count);
+	preempt_disable();
+	__count_memcg_events(memcg, idx, count);
+	preempt_enable();
 }
 
 /* idx can be of type enum memcg_event_item or vm_event_item */
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index dabbc076e503..40d1ef65fbd2 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -542,39 +542,10 @@ mem_cgroup_largest_soft_limit_node(struct mem_cgroup_tree_per_node *mctz)
 	return mz;
 }
 
-/*
- * Return page count for single (non recursive) @memcg.
- *
- * Implementation Note: reading percpu statistics for memcg.
- *
- * Both of vmstat[] and percpu_counter has threshold and do periodic
- * synchronization to implement "quick" read. There are trade-off between
- * reading cost and precision of value. Then, we may have a chance to implement
- * a periodic synchronization of counter in memcg's counter.
- *
- * But this _read() function is used for user interface now. The user accounts
- * memory usage by memory cgroup and he _always_ requires exact value because
- * he accounts memory. Even if we provide quick-and-fuzzy read, we always
- * have to visit all online cpus and make sum. So, for now, unnecessary
- * synchronization is not implemented. (just implemented for cpu hotplug)
- *
- * If there are kernel internal actions which can make use of some not-exact
- * value, and reading all cpu value can be performance bottleneck in some
- * common workload, threshold and synchronization as vmstat[] should be
- * implemented.
- *
- * The parameter idx can be of type enum memcg_event_item or vm_event_item.
- */
-
 static unsigned long memcg_sum_events(struct mem_cgroup *memcg,
 				      int event)
 {
-	unsigned long val = 0;
-	int cpu;
-
-	for_each_possible_cpu(cpu)
-		val += per_cpu(memcg->stat->events[event], cpu);
-	return val;
+	return atomic_long_read(&memcg->events[event]);
 }
 
 static void mem_cgroup_charge_statistics(struct mem_cgroup *memcg,
@@ -606,7 +577,7 @@ static void mem_cgroup_charge_statistics(struct mem_cgroup *memcg,
 		nr_pages = -nr_pages; /* for event */
 	}
 
-	__this_cpu_add(memcg->stat->nr_page_events, nr_pages);
+	__this_cpu_add(memcg->stat_cpu->nr_page_events, nr_pages);
 }
 
 unsigned long mem_cgroup_node_nr_lru_pages(struct mem_cgroup *memcg,
@@ -642,8 +613,8 @@ static bool mem_cgroup_event_ratelimit(struct mem_cgroup *memcg,
 {
 	unsigned long val, next;
 
-	val = __this_cpu_read(memcg->stat->nr_page_events);
-	next = __this_cpu_read(memcg->stat->targets[target]);
+	val = __this_cpu_read(memcg->stat_cpu->nr_page_events);
+	next = __this_cpu_read(memcg->stat_cpu->targets[target]);
 	/* from time_after() in jiffies.h */
 	if ((long)(next - val) < 0) {
 		switch (target) {
@@ -659,7 +630,7 @@ static bool mem_cgroup_event_ratelimit(struct mem_cgroup *memcg,
 		default:
 			break;
 		}
-		__this_cpu_write(memcg->stat->targets[target], next);
+		__this_cpu_write(memcg->stat_cpu->targets[target], next);
 		return true;
 	}
 	return false;
@@ -1707,11 +1678,6 @@ void unlock_page_memcg(struct page *page)
 }
 EXPORT_SYMBOL(unlock_page_memcg);
 
-/*
- * size of first charge trial. "32" comes from vmscan.c's magic value.
- * TODO: maybe necessary to use big numbers in big irons.
- */
-#define CHARGE_BATCH	32U
 struct memcg_stock_pcp {
 	struct mem_cgroup *cached; /* this never be root cgroup */
 	unsigned int nr_pages;
@@ -1739,7 +1705,7 @@ static bool consume_stock(struct mem_cgroup *memcg, unsigned int nr_pages)
 	unsigned long flags;
 	bool ret = false;
 
-	if (nr_pages > CHARGE_BATCH)
+	if (nr_pages > MEMCG_CHARGE_BATCH)
 		return ret;
 
 	local_irq_save(flags);
@@ -1808,7 +1774,7 @@ static void refill_stock(struct mem_cgroup *memcg, unsigned int nr_pages)
 	}
 	stock->nr_pages += nr_pages;
 
-	if (stock->nr_pages > CHARGE_BATCH)
+	if (stock->nr_pages > MEMCG_CHARGE_BATCH)
 		drain_stock(stock);
 
 	local_irq_restore(flags);
@@ -1858,9 +1824,44 @@ static void drain_all_stock(struct mem_cgroup *root_memcg)
 static int memcg_hotplug_cpu_dead(unsigned int cpu)
 {
 	struct memcg_stock_pcp *stock;
+	struct mem_cgroup *memcg;
 
 	stock = &per_cpu(memcg_stock, cpu);
 	drain_stock(stock);
+
+	for_each_mem_cgroup(memcg) {
+		int i;
+
+		for (i = 0; i < MEMCG_NR_STAT; i++) {
+			int nid;
+			long x;
+
+			x = __this_cpu_xchg(memcg->stat_cpu->count[i], 0);
+			if (x)
+				atomic_long_add(x, &memcg->stat[i]);
+
+			if (i >= NR_VM_NODE_STAT_ITEMS)
+				continue;
+
+			for_each_node(nid) {
+				struct mem_cgroup_per_node *pn;
+
+				pn = mem_cgroup_nodeinfo(memcg, nid);
+				x = __this_cpu_xchg(pn->lruvec_stat_cpu->count[i], 0);
+				if (x)
+					atomic_long_add(x, &pn->lruvec_stat[i]);
+			}
+		}
+
+		for (i = 0; i < MEMCG_NR_EVENTS; i++) {
+			long x;
+
+			x = __this_cpu_xchg(memcg->stat_cpu->events[i], 0);
+			if (x)
+				atomic_long_add(x, &memcg->events[i]);
+		}
+	}
+
 	return 0;
 }
 
@@ -1881,7 +1882,7 @@ static void high_work_func(struct work_struct *work)
 	struct mem_cgroup *memcg;
 
 	memcg = container_of(work, struct mem_cgroup, high_work);
-	reclaim_high(memcg, CHARGE_BATCH, GFP_KERNEL);
+	reclaim_high(memcg, MEMCG_CHARGE_BATCH, GFP_KERNEL);
 }
 
 /*
@@ -1905,7 +1906,7 @@ void mem_cgroup_handle_over_high(void)
 static int try_charge(struct mem_cgroup *memcg, gfp_t gfp_mask,
 		      unsigned int nr_pages)
 {
-	unsigned int batch = max(CHARGE_BATCH, nr_pages);
+	unsigned int batch = max(MEMCG_CHARGE_BATCH, nr_pages);
 	int nr_retries = MEM_CGROUP_RECLAIM_RETRIES;
 	struct mem_cgroup *mem_over_limit;
 	struct page_counter *counter;
@@ -4161,8 +4162,8 @@ static int alloc_mem_cgroup_per_node_info(struct mem_cgroup *memcg, int node)
 	if (!pn)
 		return 1;
 
-	pn->lruvec_stat = alloc_percpu(struct lruvec_stat);
-	if (!pn->lruvec_stat) {
+	pn->lruvec_stat_cpu = alloc_percpu(struct lruvec_stat);
+	if (!pn->lruvec_stat_cpu) {
 		kfree(pn);
 		return 1;
 	}
@@ -4180,7 +4181,7 @@ static void free_mem_cgroup_per_node_info(struct mem_cgroup *memcg, int node)
 {
 	struct mem_cgroup_per_node *pn = memcg->nodeinfo[node];
 
-	free_percpu(pn->lruvec_stat);
+	free_percpu(pn->lruvec_stat_cpu);
 	kfree(pn);
 }
 
@@ -4190,7 +4191,7 @@ static void __mem_cgroup_free(struct mem_cgroup *memcg)
 
 	for_each_node(node)
 		free_mem_cgroup_per_node_info(memcg, node);
-	free_percpu(memcg->stat);
+	free_percpu(memcg->stat_cpu);
 	kfree(memcg);
 }
 
@@ -4219,8 +4220,8 @@ static struct mem_cgroup *mem_cgroup_alloc(void)
 	if (memcg->id.id < 0)
 		goto fail;
 
-	memcg->stat = alloc_percpu(struct mem_cgroup_stat_cpu);
-	if (!memcg->stat)
+	memcg->stat_cpu = alloc_percpu(struct mem_cgroup_stat_cpu);
+	if (!memcg->stat_cpu)
 		goto fail;
 
 	for_each_node(node)
@@ -5638,7 +5639,7 @@ static void uncharge_batch(const struct uncharge_gather *ug)
 	__mod_memcg_state(ug->memcg, MEMCG_RSS_HUGE, -ug->nr_huge);
 	__mod_memcg_state(ug->memcg, NR_SHMEM, -ug->nr_shmem);
 	__count_memcg_events(ug->memcg, PGPGOUT, ug->pgpgout);
-	__this_cpu_add(ug->memcg->stat->nr_page_events, nr_pages);
+	__this_cpu_add(ug->memcg->stat_cpu->nr_page_events, nr_pages);
 	memcg_check_events(ug->memcg, ug->dummy_page);
 	local_irq_restore(flags);
 
-- 
2.15.0

[PATCH 3/3] mm: memcontrol: fix excessive complexity in memory.stat reporting

[Johannes Weiner]

We've seen memory.stat reads in top-level cgroups take up to fourteen
seconds during a userspace bug that created tens of thousands of ghost
cgroups pinned by lingering page cache.

Even with a more reasonable number of cgroups, aggregating memory.stat
is unnecessarily heavy. The complexity is this:

	nr_cgroups * nr_stat_items * nr_possible_cpus

where the stat items are ~70 at this point. With 128 cgroups and 128
CPUs - decent, not enormous setups - reading the top-level memory.stat
has to aggregate over a million per-cpu counters. This doesn't scale.

Instead of spreading the source of truth across all CPUs, use the
per-cpu counters merely to batch updates to shared atomic counters.

This is the same as the per-cpu stocks we use for charging memory to
the shared atomic page_counters, and also the way the global vmstat
counters are implemented.

Vmstat has elaborate spilling thresholds that depend on the number of
CPUs, amount of memory, and memory pressure - carefully balancing the
cost of counter updates with the amount of per-cpu error. That's
because the vmstat counters are system-wide, but also used for
decisions inside the kernel (e.g. NR_FREE_PAGES in the
allocator). Neither is true for the memory controller.

Use the same static batch size we already use for page_counter updates
during charging. The per-cpu error in the stats will be 128k, which is
an acceptable ratio of cores to memory accounting granularity.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
---
 include/linux/memcontrol.h |  96 +++++++++++++++++++++++++++---------------
 mm/memcontrol.c            | 101 +++++++++++++++++++++++----------------------
 2 files changed, 113 insertions(+), 84 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 1ffc54ac4cc9..882046863581 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -108,7 +108,10 @@ struct lruvec_stat {
  */
 struct mem_cgroup_per_node {
 	struct lruvec		lruvec;
-	struct lruvec_stat __percpu *lruvec_stat;
+
+	struct lruvec_stat __percpu *lruvec_stat_cpu;
+	atomic_long_t		lruvec_stat[NR_VM_NODE_STAT_ITEMS];
+
 	unsigned long		lru_zone_size[MAX_NR_ZONES][NR_LRU_LISTS];
 
 	struct mem_cgroup_reclaim_iter	iter[DEF_PRIORITY + 1];
@@ -227,10 +230,10 @@ struct mem_cgroup {
 	spinlock_t		move_lock;
 	struct task_struct	*move_lock_task;
 	unsigned long		move_lock_flags;
-	/*
-	 * percpu counter.
-	 */
-	struct mem_cgroup_stat_cpu __percpu *stat;
+
+	struct mem_cgroup_stat_cpu __percpu *stat_cpu;
+	atomic_long_t		stat[MEMCG_NR_STAT];
+	atomic_long_t		events[MEMCG_NR_EVENTS];
 
 	unsigned long		socket_pressure;
 
@@ -265,6 +268,12 @@ struct mem_cgroup {
 	/* WARNING: nodeinfo must be the last member here */
 };
 
+/*
+ * size of first charge trial. "32" comes from vmscan.c's magic value.
+ * TODO: maybe necessary to use big numbers in big irons.
+ */
+#define MEMCG_CHARGE_BATCH 32U
+
 extern struct mem_cgroup *root_mem_cgroup;
 
 static inline bool mem_cgroup_disabled(void)
@@ -485,32 +494,38 @@ void unlock_page_memcg(struct page *page);
 static inline unsigned long memcg_page_state(struct mem_cgroup *memcg,
 					     int idx)
 {
-	long val = 0;
-	int cpu;
-
-	for_each_possible_cpu(cpu)
-		val += per_cpu(memcg->stat->count[idx], cpu);
-
-	if (val < 0)
-		val = 0;
-
-	return val;
+	long x = atomic_long_read(&memcg->stat[idx]);
+#ifdef CONFIG_SMP
+	if (x < 0)
+		x = 0;
+#endif
+	return x;
 }
 
 /* idx can be of type enum memcg_stat_item or node_stat_item */
 static inline void __mod_memcg_state(struct mem_cgroup *memcg,
 				     int idx, int val)
 {
-	if (!mem_cgroup_disabled())
-		__this_cpu_add(memcg->stat->count[idx], val);
+	long x;
+
+	if (mem_cgroup_disabled())
+		return;
+
+	x = val + __this_cpu_read(memcg->stat_cpu->count[idx]);
+	if (unlikely(abs(x) > MEMCG_CHARGE_BATCH)) {
+		atomic_long_add(x, &memcg->stat[idx]);
+		x = 0;
+	}
+	__this_cpu_write(memcg->stat_cpu->count[idx], x);
 }
 
 /* idx can be of type enum memcg_stat_item or node_stat_item */
 static inline void mod_memcg_state(struct mem_cgroup *memcg,
 				   int idx, int val)
 {
-	if (!mem_cgroup_disabled())
-		this_cpu_add(memcg->stat->count[idx], val);
+	preempt_disable();
+	__mod_memcg_state(memcg, idx, val);
+	preempt_enable();
 }
 
 /**
@@ -548,26 +563,25 @@ static inline unsigned long lruvec_page_state(struct lruvec *lruvec,
 					      enum node_stat_item idx)
 {
 	struct mem_cgroup_per_node *pn;
-	long val = 0;
-	int cpu;
+	long x;
 
 	if (mem_cgroup_disabled())
 		return node_page_state(lruvec_pgdat(lruvec), idx);
 
 	pn = container_of(lruvec, struct mem_cgroup_per_node, lruvec);
-	for_each_possible_cpu(cpu)
-		val += per_cpu(pn->lruvec_stat->count[idx], cpu);
-
-	if (val < 0)
-		val = 0;
-
-	return val;
+	x = atomic_long_read(&pn->lruvec_stat[idx]);
+#ifdef CONFIG_SMP
+	if (x < 0)
+		x = 0;
+#endif
+	return x;
 }
 
 static inline void __mod_lruvec_state(struct lruvec *lruvec,
 				      enum node_stat_item idx, int val)
 {
 	struct mem_cgroup_per_node *pn;
+	long x;
 
 	/* Update node */
 	__mod_node_page_state(lruvec_pgdat(lruvec), idx, val);
@@ -581,7 +595,12 @@ static inline void __mod_lruvec_state(struct lruvec *lruvec,
 	__mod_memcg_state(pn->memcg, idx, val);
 
 	/* Update lruvec */
-	__this_cpu_add(pn->lruvec_stat->count[idx], val);
+	x = val + __this_cpu_read(pn->lruvec_stat_cpu->count[idx]);
+	if (unlikely(abs(x) > MEMCG_CHARGE_BATCH)) {
+		atomic_long_add(x, &pn->lruvec_stat[idx]);
+		x = 0;
+	}
+	__this_cpu_write(pn->lruvec_stat_cpu->count[idx], x);
 }
 
 static inline void mod_lruvec_state(struct lruvec *lruvec,
@@ -624,16 +643,25 @@ unsigned long mem_cgroup_soft_limit_reclaim(pg_data_t *pgdat, int order,
 static inline void __count_memcg_events(struct mem_cgroup *memcg,
 					int idx, unsigned long count)
 {
-	if (!mem_cgroup_disabled())
-		__this_cpu_add(memcg->stat->events[idx], count);
+	unsigned long x;
+
+	if (mem_cgroup_disabled())
+		return;
+
+	x = count + __this_cpu_read(memcg->stat_cpu->events[idx]);
+	if (unlikely(x > MEMCG_CHARGE_BATCH)) {
+		atomic_long_add(x, &memcg->events[idx]);
+		x = 0;
+	}
+	__this_cpu_write(memcg->stat_cpu->events[idx], x);
 }
 
-/* idx can be of type enum memcg_event_item or vm_event_item */
 static inline void count_memcg_events(struct mem_cgroup *memcg,
 				      int idx, unsigned long count)
 {
-	if (!mem_cgroup_disabled())
-		this_cpu_add(memcg->stat->events[idx], count);
+	preempt_disable();
+	__count_memcg_events(memcg, idx, count);
+	preempt_enable();
 }
 
 /* idx can be of type enum memcg_event_item or vm_event_item */
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index dabbc076e503..40d1ef65fbd2 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -542,39 +542,10 @@ mem_cgroup_largest_soft_limit_node(struct mem_cgroup_tree_per_node *mctz)
 	return mz;
 }
 
-/*
- * Return page count for single (non recursive) @memcg.
- *
- * Implementation Note: reading percpu statistics for memcg.
- *
- * Both of vmstat[] and percpu_counter has threshold and do periodic
- * synchronization to implement "quick" read. There are trade-off between
- * reading cost and precision of value. Then, we may have a chance to implement
- * a periodic synchronization of counter in memcg's counter.
- *
- * But this _read() function is used for user interface now. The user accounts
- * memory usage by memory cgroup and he _always_ requires exact value because
- * he accounts memory. Even if we provide quick-and-fuzzy read, we always
- * have to visit all online cpus and make sum. So, for now, unnecessary
- * synchronization is not implemented. (just implemented for cpu hotplug)
- *
- * If there are kernel internal actions which can make use of some not-exact
- * value, and reading all cpu value can be performance bottleneck in some
- * common workload, threshold and synchronization as vmstat[] should be
- * implemented.
- *
- * The parameter idx can be of type enum memcg_event_item or vm_event_item.
- */
-
 static unsigned long memcg_sum_events(struct mem_cgroup *memcg,
 				      int event)
 {
-	unsigned long val = 0;
-	int cpu;
-
-	for_each_possible_cpu(cpu)
-		val += per_cpu(memcg->stat->events[event], cpu);
-	return val;
+	return atomic_long_read(&memcg->events[event]);
 }
 
 static void mem_cgroup_charge_statistics(struct mem_cgroup *memcg,
@@ -606,7 +577,7 @@ static void mem_cgroup_charge_statistics(struct mem_cgroup *memcg,
 		nr_pages = -nr_pages; /* for event */
 	}
 
-	__this_cpu_add(memcg->stat->nr_page_events, nr_pages);
+	__this_cpu_add(memcg->stat_cpu->nr_page_events, nr_pages);
 }
 
 unsigned long mem_cgroup_node_nr_lru_pages(struct mem_cgroup *memcg,
@@ -642,8 +613,8 @@ static bool mem_cgroup_event_ratelimit(struct mem_cgroup *memcg,
 {
 	unsigned long val, next;
 
-	val = __this_cpu_read(memcg->stat->nr_page_events);
-	next = __this_cpu_read(memcg->stat->targets[target]);
+	val = __this_cpu_read(memcg->stat_cpu->nr_page_events);
+	next = __this_cpu_read(memcg->stat_cpu->targets[target]);
 	/* from time_after() in jiffies.h */
 	if ((long)(next - val) < 0) {
 		switch (target) {
@@ -659,7 +630,7 @@ static bool mem_cgroup_event_ratelimit(struct mem_cgroup *memcg,
 		default:
 			break;
 		}
-		__this_cpu_write(memcg->stat->targets[target], next);
+		__this_cpu_write(memcg->stat_cpu->targets[target], next);
 		return true;
 	}
 	return false;
@@ -1707,11 +1678,6 @@ void unlock_page_memcg(struct page *page)
 }
 EXPORT_SYMBOL(unlock_page_memcg);
 
-/*
- * size of first charge trial. "32" comes from vmscan.c's magic value.
- * TODO: maybe necessary to use big numbers in big irons.
- */
-#define CHARGE_BATCH	32U
 struct memcg_stock_pcp {
 	struct mem_cgroup *cached; /* this never be root cgroup */
 	unsigned int nr_pages;
@@ -1739,7 +1705,7 @@ static bool consume_stock(struct mem_cgroup *memcg, unsigned int nr_pages)
 	unsigned long flags;
 	bool ret = false;
 
-	if (nr_pages > CHARGE_BATCH)
+	if (nr_pages > MEMCG_CHARGE_BATCH)
 		return ret;
 
 	local_irq_save(flags);
@@ -1808,7 +1774,7 @@ static void refill_stock(struct mem_cgroup *memcg, unsigned int nr_pages)
 	}
 	stock->nr_pages += nr_pages;
 
-	if (stock->nr_pages > CHARGE_BATCH)
+	if (stock->nr_pages > MEMCG_CHARGE_BATCH)
 		drain_stock(stock);
 
 	local_irq_restore(flags);
@@ -1858,9 +1824,44 @@ static void drain_all_stock(struct mem_cgroup *root_memcg)
 static int memcg_hotplug_cpu_dead(unsigned int cpu)
 {
 	struct memcg_stock_pcp *stock;
+	struct mem_cgroup *memcg;
 
 	stock = &per_cpu(memcg_stock, cpu);
 	drain_stock(stock);
+
+	for_each_mem_cgroup(memcg) {
+		int i;
+
+		for (i = 0; i < MEMCG_NR_STAT; i++) {
+			int nid;
+			long x;
+
+			x = __this_cpu_xchg(memcg->stat_cpu->count[i], 0);
+			if (x)
+				atomic_long_add(x, &memcg->stat[i]);
+
+			if (i >= NR_VM_NODE_STAT_ITEMS)
+				continue;
+
+			for_each_node(nid) {
+				struct mem_cgroup_per_node *pn;
+
+				pn = mem_cgroup_nodeinfo(memcg, nid);
+				x = __this_cpu_xchg(pn->lruvec_stat_cpu->count[i], 0);
+				if (x)
+					atomic_long_add(x, &pn->lruvec_stat[i]);
+			}
+		}
+
+		for (i = 0; i < MEMCG_NR_EVENTS; i++) {
+			long x;
+
+			x = __this_cpu_xchg(memcg->stat_cpu->events[i], 0);
+			if (x)
+				atomic_long_add(x, &memcg->events[i]);
+		}
+	}
+
 	return 0;
 }
 
@@ -1881,7 +1882,7 @@ static void high_work_func(struct work_struct *work)
 	struct mem_cgroup *memcg;
 
 	memcg = container_of(work, struct mem_cgroup, high_work);
-	reclaim_high(memcg, CHARGE_BATCH, GFP_KERNEL);
+	reclaim_high(memcg, MEMCG_CHARGE_BATCH, GFP_KERNEL);
 }
 
 /*
@@ -1905,7 +1906,7 @@ void mem_cgroup_handle_over_high(void)
 static int try_charge(struct mem_cgroup *memcg, gfp_t gfp_mask,
 		      unsigned int nr_pages)
 {
-	unsigned int batch = max(CHARGE_BATCH, nr_pages);
+	unsigned int batch = max(MEMCG_CHARGE_BATCH, nr_pages);
 	int nr_retries = MEM_CGROUP_RECLAIM_RETRIES;
 	struct mem_cgroup *mem_over_limit;
 	struct page_counter *counter;
@@ -4161,8 +4162,8 @@ static int alloc_mem_cgroup_per_node_info(struct mem_cgroup *memcg, int node)
 	if (!pn)
 		return 1;
 
-	pn->lruvec_stat = alloc_percpu(struct lruvec_stat);
-	if (!pn->lruvec_stat) {
+	pn->lruvec_stat_cpu = alloc_percpu(struct lruvec_stat);
+	if (!pn->lruvec_stat_cpu) {
 		kfree(pn);
 		return 1;
 	}
@@ -4180,7 +4181,7 @@ static void free_mem_cgroup_per_node_info(struct mem_cgroup *memcg, int node)
 {
 	struct mem_cgroup_per_node *pn = memcg->nodeinfo[node];
 
-	free_percpu(pn->lruvec_stat);
+	free_percpu(pn->lruvec_stat_cpu);
 	kfree(pn);
 }
 
@@ -4190,7 +4191,7 @@ static void __mem_cgroup_free(struct mem_cgroup *memcg)
 
 	for_each_node(node)
 		free_mem_cgroup_per_node_info(memcg, node);
-	free_percpu(memcg->stat);
+	free_percpu(memcg->stat_cpu);
 	kfree(memcg);
 }
 
@@ -4219,8 +4220,8 @@ static struct mem_cgroup *mem_cgroup_alloc(void)
 	if (memcg->id.id < 0)
 		goto fail;
 
-	memcg->stat = alloc_percpu(struct mem_cgroup_stat_cpu);
-	if (!memcg->stat)
+	memcg->stat_cpu = alloc_percpu(struct mem_cgroup_stat_cpu);
+	if (!memcg->stat_cpu)
 		goto fail;
 
 	for_each_node(node)
@@ -5638,7 +5639,7 @@ static void uncharge_batch(const struct uncharge_gather *ug)
 	__mod_memcg_state(ug->memcg, MEMCG_RSS_HUGE, -ug->nr_huge);
 	__mod_memcg_state(ug->memcg, NR_SHMEM, -ug->nr_shmem);
 	__count_memcg_events(ug->memcg, PGPGOUT, ug->pgpgout);
-	__this_cpu_add(ug->memcg->stat->nr_page_events, nr_pages);
+	__this_cpu_add(ug->memcg->stat_cpu->nr_page_events, nr_pages);
 	memcg_check_events(ug->memcg, ug->dummy_page);
 	local_irq_restore(flags);
 
-- 
2.15.0

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Re: [PATCH 1/3] mm: memcontrol: eliminate raw access to stat and event counters

[Vladimir Davydov]

On Fri, Nov 03, 2017 at 11:33:34AM -0400, Johannes Weiner wrote:
> Replace all raw 'this_cpu_' modifications of the stat and event
> per-cpu counters with API functions such as mod_memcg_state().
> 
> This makes the code easier to read, but is also in preparation for the
> next patch, which changes the per-cpu implementation of those counters.
> 
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
> ---
>  include/linux/memcontrol.h | 31 +++++++++++++++---------
>  mm/memcontrol.c            | 59 ++++++++++++++++++++--------------------------
>  2 files changed, 45 insertions(+), 45 deletions(-)

Acked-by: Vladimir Davydov <vdavydov.dev@gmail.com>

Re: [PATCH 1/3] mm: memcontrol: eliminate raw access to stat and event counters

[Vladimir Davydov]

On Fri, Nov 03, 2017 at 11:33:34AM -0400, Johannes Weiner wrote:
> Replace all raw 'this_cpu_' modifications of the stat and event
> per-cpu counters with API functions such as mod_memcg_state().
> 
> This makes the code easier to read, but is also in preparation for the
> next patch, which changes the per-cpu implementation of those counters.
> 
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
> ---
>  include/linux/memcontrol.h | 31 +++++++++++++++---------
>  mm/memcontrol.c            | 59 ++++++++++++++++++++--------------------------
>  2 files changed, 45 insertions(+), 45 deletions(-)

Acked-by: Vladimir Davydov <vdavydov.dev@gmail.com>

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Re: [PATCH 2/3] mm: memcontrol: implement lruvec stat functions on top of each other

[Vladimir Davydov]

On Fri, Nov 03, 2017 at 11:33:35AM -0400, Johannes Weiner wrote:
> The implementation of the lruvec stat functions and their variants for
> accounting through a page, or accounting from a preemptible context,
> are mostly identical and needlessly repetitive.
> 
> Implement the lruvec_page functions by looking up the page's lruvec
> and then using the lruvec function.
> 
> Implement the functions for preemptible contexts by disabling
> preemption before calling the atomic context functions.
> 
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
> ---
>  include/linux/memcontrol.h | 44 ++++++++++++++++++++++----------------------
>  1 file changed, 22 insertions(+), 22 deletions(-)

Acked-by: Vladimir Davydov <vdavydov.dev@gmail.com>

Re: [PATCH 2/3] mm: memcontrol: implement lruvec stat functions on top of each other

[Vladimir Davydov]

On Fri, Nov 03, 2017 at 11:33:35AM -0400, Johannes Weiner wrote:
> The implementation of the lruvec stat functions and their variants for
> accounting through a page, or accounting from a preemptible context,
> are mostly identical and needlessly repetitive.
> 
> Implement the lruvec_page functions by looking up the page's lruvec
> and then using the lruvec function.
> 
> Implement the functions for preemptible contexts by disabling
> preemption before calling the atomic context functions.
> 
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
> ---
>  include/linux/memcontrol.h | 44 ++++++++++++++++++++++----------------------
>  1 file changed, 22 insertions(+), 22 deletions(-)

Acked-by: Vladimir Davydov <vdavydov.dev@gmail.com>

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Re: [PATCH 3/3] mm: memcontrol: fix excessive complexity in memory.stat reporting

[Vladimir Davydov]

On Fri, Nov 03, 2017 at 11:33:36AM -0400, Johannes Weiner wrote:
> We've seen memory.stat reads in top-level cgroups take up to fourteen
> seconds during a userspace bug that created tens of thousands of ghost
> cgroups pinned by lingering page cache.
> 
> Even with a more reasonable number of cgroups, aggregating memory.stat
> is unnecessarily heavy. The complexity is this:
> 
> 	nr_cgroups * nr_stat_items * nr_possible_cpus
> 
> where the stat items are ~70 at this point. With 128 cgroups and 128
> CPUs - decent, not enormous setups - reading the top-level memory.stat
> has to aggregate over a million per-cpu counters. This doesn't scale.
> 
> Instead of spreading the source of truth across all CPUs, use the
> per-cpu counters merely to batch updates to shared atomic counters.
> 
> This is the same as the per-cpu stocks we use for charging memory to
> the shared atomic page_counters, and also the way the global vmstat
> counters are implemented.
> 
> Vmstat has elaborate spilling thresholds that depend on the number of
> CPUs, amount of memory, and memory pressure - carefully balancing the
> cost of counter updates with the amount of per-cpu error. That's
> because the vmstat counters are system-wide, but also used for
> decisions inside the kernel (e.g. NR_FREE_PAGES in the
> allocator). Neither is true for the memory controller.
> 
> Use the same static batch size we already use for page_counter updates
> during charging. The per-cpu error in the stats will be 128k, which is
> an acceptable ratio of cores to memory accounting granularity.
> 
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
> ---
>  include/linux/memcontrol.h |  96 +++++++++++++++++++++++++++---------------
>  mm/memcontrol.c            | 101 +++++++++++++++++++++++----------------------
>  2 files changed, 113 insertions(+), 84 deletions(-)

Acked-by: Vladimir Davydov <vdavydov.dev@gmail.com>

Re: [PATCH 3/3] mm: memcontrol: fix excessive complexity in memory.stat reporting

[Vladimir Davydov]

On Fri, Nov 03, 2017 at 11:33:36AM -0400, Johannes Weiner wrote:
> We've seen memory.stat reads in top-level cgroups take up to fourteen
> seconds during a userspace bug that created tens of thousands of ghost
> cgroups pinned by lingering page cache.
> 
> Even with a more reasonable number of cgroups, aggregating memory.stat
> is unnecessarily heavy. The complexity is this:
> 
> 	nr_cgroups * nr_stat_items * nr_possible_cpus
> 
> where the stat items are ~70 at this point. With 128 cgroups and 128
> CPUs - decent, not enormous setups - reading the top-level memory.stat
> has to aggregate over a million per-cpu counters. This doesn't scale.
> 
> Instead of spreading the source of truth across all CPUs, use the
> per-cpu counters merely to batch updates to shared atomic counters.
> 
> This is the same as the per-cpu stocks we use for charging memory to
> the shared atomic page_counters, and also the way the global vmstat
> counters are implemented.
> 
> Vmstat has elaborate spilling thresholds that depend on the number of
> CPUs, amount of memory, and memory pressure - carefully balancing the
> cost of counter updates with the amount of per-cpu error. That's
> because the vmstat counters are system-wide, but also used for
> decisions inside the kernel (e.g. NR_FREE_PAGES in the
> allocator). Neither is true for the memory controller.
> 
> Use the same static batch size we already use for page_counter updates
> during charging. The per-cpu error in the stats will be 128k, which is
> an acceptable ratio of cores to memory accounting granularity.
> 
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
> ---
>  include/linux/memcontrol.h |  96 +++++++++++++++++++++++++++---------------
>  mm/memcontrol.c            | 101 +++++++++++++++++++++++----------------------
>  2 files changed, 113 insertions(+), 84 deletions(-)

Acked-by: Vladimir Davydov <vdavydov.dev@gmail.com>

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