[PATCH 0/4] mm/list_lru: Add list_lru_shrink_walk_irq() and a user

[PATCH 0/4] mm/list_lru: Add list_lru_shrink_walk_irq() and a user

[Sebastian Andrzej Siewior]

This series removes the local_irq_disable() around
list_lru_shrink_walk() (as used by mm/workingset) by adding
list_lru_shrink_walk_irq(). Vladimir Davydov preferred this over an `irq'
argument which I added to struct list_lru.

The initial post (of this series) received a Reviewed-by tag by Vladimir
Davydov which I added to each patch of the series.
The series applies on top of akpm's tree which has Kirill's shrink_slab
series and does not clash with it (akpm asked me to wait a week or so
and repost it then).

I tested the code paths by triggering the OOM-killer via memory over
commit and lockdep did not complain (nor did I see any warnings).

Sebastian

Sebastian

[PATCH 1/4] mm/list_lru: use list_lru_walk_one() in list_lru_walk_node()

[Sebastian Andrzej Siewior]

list_lru_walk_node() invokes __list_lru_walk_one() with -1 as the
memcg_idx parameter. The same can be achieved by list_lru_walk_one() and
passing NULL as memcg argument which then gets converted into -1. This
is a preparation step when the spin_lock() function is lifted to the
caller of __list_lru_walk_one().
Invoke list_lru_walk_one() instead __list_lru_walk_one() when possible.

Reviewed-by: Vladimir Davydov <vdavydov.dev@gmail.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 mm/list_lru.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/list_lru.c b/mm/list_lru.c
index ca6dbcfe4256..344306714636 100644
--- a/mm/list_lru.c
+++ b/mm/list_lru.c
@@ -294,8 +294,8 @@ unsigned long list_lru_walk_node(struct list_lru *lru, int nid,
 	long isolated = 0;
 	int memcg_idx;
 
-	isolated += __list_lru_walk_one(lru, nid, -1, isolate, cb_arg,
-					nr_to_walk);
+	isolated += list_lru_walk_one(lru, nid, NULL, isolate, cb_arg,
+				      nr_to_walk);
 	if (*nr_to_walk > 0 && list_lru_memcg_aware(lru)) {
 		for_each_memcg_cache_index(memcg_idx) {
 			isolated += __list_lru_walk_one(lru, nid, memcg_idx,
-- 
2.18.0

[PATCH 2/4] mm/list_lru: Move locking from __list_lru_walk_one() to its caller

[Sebastian Andrzej Siewior]

Move the locking inside __list_lru_walk_one() to its caller. This is a
preparation step in order to introduce list_lru_walk_one_irq() which
does spin_lock_irq() instead of spin_lock() for the locking.

Reviewed-by: Vladimir Davydov <vdavydov.dev@gmail.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 mm/list_lru.c | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/mm/list_lru.c b/mm/list_lru.c
index 344306714636..3e36e7a239e5 100644
--- a/mm/list_lru.c
+++ b/mm/list_lru.c
@@ -226,7 +226,6 @@ __list_lru_walk_one(struct list_lru *lru, int nid, int memcg_idx,
 	struct list_head *item, *n;
 	unsigned long isolated = 0;
 
-	spin_lock(&nlru->lock);
 	l = list_lru_from_memcg_idx(nlru, memcg_idx);
 restart:
 	list_for_each_safe(item, n, &l->list) {
@@ -272,8 +271,6 @@ __list_lru_walk_one(struct list_lru *lru, int nid, int memcg_idx,
 			BUG();
 		}
 	}
-
-	spin_unlock(&nlru->lock);
 	return isolated;
 }
 
@@ -282,8 +279,14 @@ list_lru_walk_one(struct list_lru *lru, int nid, struct mem_cgroup *memcg,
 		  list_lru_walk_cb isolate, void *cb_arg,
 		  unsigned long *nr_to_walk)
 {
-	return __list_lru_walk_one(lru, nid, memcg_cache_id(memcg),
-				   isolate, cb_arg, nr_to_walk);
+	struct list_lru_node *nlru = &lru->node[nid];
+	unsigned long ret;
+
+	spin_lock(&nlru->lock);
+	ret = __list_lru_walk_one(lru, nid, memcg_cache_id(memcg),
+				  isolate, cb_arg, nr_to_walk);
+	spin_unlock(&nlru->lock);
+	return ret;
 }
 EXPORT_SYMBOL_GPL(list_lru_walk_one);
 
@@ -298,8 +301,13 @@ unsigned long list_lru_walk_node(struct list_lru *lru, int nid,
 				      nr_to_walk);
 	if (*nr_to_walk > 0 && list_lru_memcg_aware(lru)) {
 		for_each_memcg_cache_index(memcg_idx) {
+			struct list_lru_node *nlru = &lru->node[nid];
+
+			spin_lock(&nlru->lock);
 			isolated += __list_lru_walk_one(lru, nid, memcg_idx,
 						isolate, cb_arg, nr_to_walk);
+			spin_unlock(&nlru->lock);
+
 			if (*nr_to_walk <= 0)
 				break;
 		}
-- 
2.18.0

[PATCH 3/4] mm/list_lru: Pass struct list_lru_node as an argument __list_lru_walk_one()

[Sebastian Andrzej Siewior]

__list_lru_walk_one() is invoked with struct list_lru *lru, int nid as
the first two argument. Those two are only used to retrieve struct
list_lru_node. Since this is already done by the caller of the function
for the locking, we can pass struct list_lru_node directly and avoid the
dance around it.

Reviewed-by: Vladimir Davydov <vdavydov.dev@gmail.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 mm/list_lru.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/mm/list_lru.c b/mm/list_lru.c
index 3e36e7a239e5..7b7a737f0963 100644
--- a/mm/list_lru.c
+++ b/mm/list_lru.c
@@ -216,12 +216,11 @@ unsigned long list_lru_count_node(struct list_lru *lru, int nid)
 EXPORT_SYMBOL_GPL(list_lru_count_node);
 
 static unsigned long
-__list_lru_walk_one(struct list_lru *lru, int nid, int memcg_idx,
+__list_lru_walk_one(struct list_lru_node *nlru, int memcg_idx,
 		    list_lru_walk_cb isolate, void *cb_arg,
 		    unsigned long *nr_to_walk)
 {
 
-	struct list_lru_node *nlru = &lru->node[nid];
 	struct list_lru_one *l;
 	struct list_head *item, *n;
 	unsigned long isolated = 0;
@@ -283,8 +282,8 @@ list_lru_walk_one(struct list_lru *lru, int nid, struct mem_cgroup *memcg,
 	unsigned long ret;
 
 	spin_lock(&nlru->lock);
-	ret = __list_lru_walk_one(lru, nid, memcg_cache_id(memcg),
-				  isolate, cb_arg, nr_to_walk);
+	ret = __list_lru_walk_one(nlru, memcg_cache_id(memcg), isolate, cb_arg,
+				  nr_to_walk);
 	spin_unlock(&nlru->lock);
 	return ret;
 }
@@ -304,8 +303,9 @@ unsigned long list_lru_walk_node(struct list_lru *lru, int nid,
 			struct list_lru_node *nlru = &lru->node[nid];
 
 			spin_lock(&nlru->lock);
-			isolated += __list_lru_walk_one(lru, nid, memcg_idx,
-						isolate, cb_arg, nr_to_walk);
+			isolated += __list_lru_walk_one(nlru, memcg_idx,
+							isolate, cb_arg,
+							nr_to_walk);
 			spin_unlock(&nlru->lock);
 
 			if (*nr_to_walk <= 0)
-- 
2.18.0

[PATCH 4/4] mm/list_lru: Introduce list_lru_shrink_walk_irq()

[Sebastian Andrzej Siewior]

Provide list_lru_shrink_walk_irq() and let it behave like
list_lru_walk_one() except that it locks the spinlock with
spin_lock_irq(). This is used by scan_shadow_nodes() because its lock
nests within the i_pages lock which is acquired with IRQ.
This change allows to use proper locking promitives instead hand crafted
lock_irq_disable() plus spin_lock().
There is no EXPORT_SYMBOL provided because the current user is in-KERNEL
only.

Add list_lru_shrink_walk_irq() which acquires the spinlock with the
proper locking primitives.

Reviewed-by: Vladimir Davydov <vdavydov.dev@gmail.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 include/linux/list_lru.h | 25 +++++++++++++++++++++++++
 mm/list_lru.c            | 15 +++++++++++++++
 mm/workingset.c          |  8 ++------
 3 files changed, 42 insertions(+), 6 deletions(-)

diff --git a/include/linux/list_lru.h b/include/linux/list_lru.h
index d9c16f2f2f00..aa5efd9351eb 100644
--- a/include/linux/list_lru.h
+++ b/include/linux/list_lru.h
@@ -166,6 +166,23 @@ unsigned long list_lru_walk_one(struct list_lru *lru,
 				int nid, struct mem_cgroup *memcg,
 				list_lru_walk_cb isolate, void *cb_arg,
 				unsigned long *nr_to_walk);
+/**
+ * list_lru_walk_one_irq: walk a list_lru, isolating and disposing freeable items.
+ * @lru: the lru pointer.
+ * @nid: the node id to scan from.
+ * @memcg: the cgroup to scan from.
+ * @isolate: callback function that is resposible for deciding what to do with
+ *  the item currently being scanned
+ * @cb_arg: opaque type that will be passed to @isolate
+ * @nr_to_walk: how many items to scan.
+ *
+ * Same as @list_lru_walk_one except that the spinlock is acquired with
+ * spin_lock_irq().
+ */
+unsigned long list_lru_walk_one_irq(struct list_lru *lru,
+				    int nid, struct mem_cgroup *memcg,
+				    list_lru_walk_cb isolate, void *cb_arg,
+				    unsigned long *nr_to_walk);
 unsigned long list_lru_walk_node(struct list_lru *lru, int nid,
 				 list_lru_walk_cb isolate, void *cb_arg,
 				 unsigned long *nr_to_walk);
@@ -178,6 +195,14 @@ list_lru_shrink_walk(struct list_lru *lru, struct shrink_control *sc,
 				 &sc->nr_to_scan);
 }
 
+static inline unsigned long
+list_lru_shrink_walk_irq(struct list_lru *lru, struct shrink_control *sc,
+			 list_lru_walk_cb isolate, void *cb_arg)
+{
+	return list_lru_walk_one_irq(lru, sc->nid, sc->memcg, isolate, cb_arg,
+				     &sc->nr_to_scan);
+}
+
 static inline unsigned long
 list_lru_walk(struct list_lru *lru, list_lru_walk_cb isolate,
 	      void *cb_arg, unsigned long nr_to_walk)
diff --git a/mm/list_lru.c b/mm/list_lru.c
index 7b7a737f0963..89349a0276de 100644
--- a/mm/list_lru.c
+++ b/mm/list_lru.c
@@ -289,6 +289,21 @@ list_lru_walk_one(struct list_lru *lru, int nid, struct mem_cgroup *memcg,
 }
 EXPORT_SYMBOL_GPL(list_lru_walk_one);
 
+unsigned long
+list_lru_walk_one_irq(struct list_lru *lru, int nid, struct mem_cgroup *memcg,
+		      list_lru_walk_cb isolate, void *cb_arg,
+		      unsigned long *nr_to_walk)
+{
+	struct list_lru_node *nlru = &lru->node[nid];
+	unsigned long ret;
+
+	spin_lock_irq(&nlru->lock);
+	ret = __list_lru_walk_one(nlru, memcg_cache_id(memcg), isolate, cb_arg,
+				  nr_to_walk);
+	spin_unlock_irq(&nlru->lock);
+	return ret;
+}
+
 unsigned long list_lru_walk_node(struct list_lru *lru, int nid,
 				 list_lru_walk_cb isolate, void *cb_arg,
 				 unsigned long *nr_to_walk)
diff --git a/mm/workingset.c b/mm/workingset.c
index 06b45147e892..0b4f471d07ba 100644
--- a/mm/workingset.c
+++ b/mm/workingset.c
@@ -501,13 +501,9 @@ static enum lru_status shadow_lru_isolate(struct list_head *item,
 static unsigned long scan_shadow_nodes(struct shrinker *shrinker,
 				       struct shrink_control *sc)
 {
-	unsigned long ret;
-
 	/* list_lru lock nests inside the IRQ-safe i_pages lock */
-	local_irq_disable();
-	ret = list_lru_shrink_walk(&shadow_nodes, sc, shadow_lru_isolate, NULL);
-	local_irq_enable();
-	return ret;
+	return list_lru_shrink_walk_irq(&shadow_nodes, sc, shadow_lru_isolate,
+					NULL);
 }
 
 static struct shrinker workingset_shadow_shrinker = {
-- 
2.18.0