list_lru: add helpers to isolate items

Currently, the isolate callback passed to the list_lru_walk family of
functions is supposed to just delete an item from the list upon returning
LRU_REMOVED or LRU_REMOVED_RETRY, while nr_items counter is fixed by
__list_lru_walk_one after the callback returns.  Since the callback is
allowed to drop the lock after removing an item (it has to return
LRU_REMOVED_RETRY then), the nr_items can be less than the actual number
of elements on the list even if we check them under the lock.  This makes
it difficult to move items from one list_lru_one to another, which is
required for per-memcg list_lru reparenting - we can't just splice the
lists, we have to move entries one by one.

This patch therefore introduces helpers that must be used by callback
functions to isolate items instead of raw list_del/list_move.  These are
list_lru_isolate and list_lru_isolate_move.  They not only remove the
entry from the list, but also fix the nr_items counter, making sure
nr_items always reflects the actual number of elements on the list if
checked under the appropriate lock.

Signed-off-by: Vladimir Davydov <vdavydov@parallels.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Tejun Heo <tj@kernel.org>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Dave Chinner <david@fromorbit.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/dcache.c

@@ -400,19 +400,20 @@ static void d_shrink_add(struct dentry *dentry, struct list_head *list)
  * LRU lists entirely, while shrink_move moves it to the indicated
  * private list.
  */
-static void d_lru_isolate(struct dentry *dentry)
+static void d_lru_isolate(struct list_lru_one *lru, struct dentry *dentry)
 {
 	D_FLAG_VERIFY(dentry, DCACHE_LRU_LIST);
 	dentry->d_flags &= ~DCACHE_LRU_LIST;
 	this_cpu_dec(nr_dentry_unused);
-	list_del_init(&dentry->d_lru);
+	list_lru_isolate(lru, &dentry->d_lru);
 }
 
-static void d_lru_shrink_move(struct dentry *dentry, struct list_head *list)
+static void d_lru_shrink_move(struct list_lru_one *lru, struct dentry *dentry,
+			      struct list_head *list)
 {
 	D_FLAG_VERIFY(dentry, DCACHE_LRU_LIST);
 	dentry->d_flags |= DCACHE_SHRINK_LIST;
-	list_move_tail(&dentry->d_lru, list);
+	list_lru_isolate_move(lru, &dentry->d_lru, list);
 }
 
 /*
@@ -869,8 +870,8 @@ static void shrink_dentry_list(struct list_head *list)
 	}
 }
 
-static enum lru_status
-dentry_lru_isolate(struct list_head *item, spinlock_t *lru_lock, void *arg)
+static enum lru_status dentry_lru_isolate(struct list_head *item,
+		struct list_lru_one *lru, spinlock_t *lru_lock, void *arg)
 {
 	struct list_head *freeable = arg;
 	struct dentry	*dentry = container_of(item, struct dentry, d_lru);
@@ -890,7 +891,7 @@ dentry_lru_isolate(struct list_head *item, spinlock_t *lru_lock, void *arg)
 	 * another pass through the LRU.
 	 */
 	if (dentry->d_lockref.count) {
-		d_lru_isolate(dentry);
+		d_lru_isolate(lru, dentry);
 		spin_unlock(&dentry->d_lock);
 		return LRU_REMOVED;
 	}
@@ -921,7 +922,7 @@ dentry_lru_isolate(struct list_head *item, spinlock_t *lru_lock, void *arg)
 		return LRU_ROTATE;
 	}
 
-	d_lru_shrink_move(dentry, freeable);
+	d_lru_shrink_move(lru, dentry, freeable);
 	spin_unlock(&dentry->d_lock);
 
 	return LRU_REMOVED;
@@ -951,7 +952,7 @@ long prune_dcache_sb(struct super_block *sb, struct shrink_control *sc)
 }
 
 static enum lru_status dentry_lru_isolate_shrink(struct list_head *item,
-						spinlock_t *lru_lock, void *arg)
+		struct list_lru_one *lru, spinlock_t *lru_lock, void *arg)
 {
 	struct list_head *freeable = arg;
 	struct dentry	*dentry = container_of(item, struct dentry, d_lru);
@@ -964,7 +965,7 @@ static enum lru_status dentry_lru_isolate_shrink(struct list_head *item,
 	if (!spin_trylock(&dentry->d_lock))
 		return LRU_SKIP;
 
-	d_lru_shrink_move(dentry, freeable);
+	d_lru_shrink_move(lru, dentry, freeable);
 	spin_unlock(&dentry->d_lock);
 
 	return LRU_REMOVED;

fs/gfs2/quota.c

@@ -145,7 +145,8 @@ static void gfs2_qd_dispose(struct list_head *list)
 }
 
 
-static enum lru_status gfs2_qd_isolate(struct list_head *item, spinlock_t *lock, void *arg)
+static enum lru_status gfs2_qd_isolate(struct list_head *item,
+		struct list_lru_one *lru, spinlock_t *lru_lock, void *arg)
 {
 	struct list_head *dispose = arg;
 	struct gfs2_quota_data *qd = list_entry(item, struct gfs2_quota_data, qd_lru);
@@ -155,7 +156,7 @@ static enum lru_status gfs2_qd_isolate(struct list_head *item, spinlock_t *lock,
 
 	if (qd->qd_lockref.count == 0) {
 		lockref_mark_dead(&qd->qd_lockref);
-		list_move(&qd->qd_lru, dispose);
+		list_lru_isolate_move(lru, &qd->qd_lru, dispose);
 	}
 
 	spin_unlock(&qd->qd_lockref.lock);

fs/inode.c

@@ -685,8 +685,8 @@ int invalidate_inodes(struct super_block *sb, bool kill_dirty)
  * LRU does not have strict ordering. Hence we don't want to reclaim inodes
  * with this flag set because they are the inodes that are out of order.
  */
-static enum lru_status
-inode_lru_isolate(struct list_head *item, spinlock_t *lru_lock, void *arg)
+static enum lru_status inode_lru_isolate(struct list_head *item,
+		struct list_lru_one *lru, spinlock_t *lru_lock, void *arg)
 {
 	struct list_head *freeable = arg;
 	struct inode	*inode = container_of(item, struct inode, i_lru);
@@ -704,7 +704,7 @@ inode_lru_isolate(struct list_head *item, spinlock_t *lru_lock, void *arg)
 	 */
 	if (atomic_read(&inode->i_count) ||
 	    (inode->i_state & ~I_REFERENCED)) {
-		list_del_init(&inode->i_lru);
+		list_lru_isolate(lru, &inode->i_lru);
 		spin_unlock(&inode->i_lock);
 		this_cpu_dec(nr_unused);
 		return LRU_REMOVED;
@@ -738,7 +738,7 @@ inode_lru_isolate(struct list_head *item, spinlock_t *lru_lock, void *arg)
 
 	WARN_ON(inode->i_state & I_NEW);
 	inode->i_state |= I_FREEING;
-	list_move(&inode->i_lru, freeable);
+	list_lru_isolate_move(lru, &inode->i_lru, freeable);
 	spin_unlock(&inode->i_lock);
 
 	this_cpu_dec(nr_unused);

fs/xfs/xfs_buf.c

@@ -1488,6 +1488,7 @@ xfs_buf_iomove(
 static enum lru_status
 xfs_buftarg_wait_rele(
 	struct list_head	*item,
+	struct list_lru_one	*lru,
 	spinlock_t		*lru_lock,
 	void			*arg)
 
@@ -1509,7 +1510,7 @@ xfs_buftarg_wait_rele(
 	 */
 	atomic_set(&bp->b_lru_ref, 0);
 	bp->b_state |= XFS_BSTATE_DISPOSE;
-	list_move(item, dispose);
+	list_lru_isolate_move(lru, item, dispose);
 	spin_unlock(&bp->b_lock);
 	return LRU_REMOVED;
 }
@@ -1546,6 +1547,7 @@ xfs_wait_buftarg(
 static enum lru_status
 xfs_buftarg_isolate(
 	struct list_head	*item,
+	struct list_lru_one	*lru,
 	spinlock_t		*lru_lock,
 	void			*arg)
 {
@@ -1569,7 +1571,7 @@ xfs_buftarg_isolate(
 	}
 
 	bp->b_state |= XFS_BSTATE_DISPOSE;
-	list_move(item, dispose);
+	list_lru_isolate_move(lru, item, dispose);
 	spin_unlock(&bp->b_lock);
 	return LRU_REMOVED;
 }

fs/xfs/xfs_qm.c

@@ -430,6 +430,7 @@ struct xfs_qm_isolate {
 static enum lru_status
 xfs_qm_dquot_isolate(
 	struct list_head	*item,
+	struct list_lru_one	*lru,
 	spinlock_t		*lru_lock,
 	void			*arg)
 		__releases(lru_lock) __acquires(lru_lock)
@@ -450,7 +451,7 @@ xfs_qm_dquot_isolate(
 		XFS_STATS_INC(xs_qm_dqwants);
 
 		trace_xfs_dqreclaim_want(dqp);
-		list_del_init(&dqp->q_lru);
+		list_lru_isolate(lru, &dqp->q_lru);
 		XFS_STATS_DEC(xs_qm_dquot_unused);
 		return LRU_REMOVED;
 	}
@@ -494,7 +495,7 @@ xfs_qm_dquot_isolate(
 	xfs_dqunlock(dqp);
 
 	ASSERT(dqp->q_nrefs == 0);
-	list_move_tail(&dqp->q_lru, &isol->dispose);
+	list_lru_isolate_move(lru, &dqp->q_lru, &isol->dispose);
 	XFS_STATS_DEC(xs_qm_dquot_unused);
 	trace_xfs_dqreclaim_done(dqp);
 	XFS_STATS_INC(xs_qm_dqreclaims);

include/linux/list_lru.h

@@ -125,8 +125,13 @@ static inline unsigned long list_lru_count(struct list_lru *lru)
 	return count;
 }
 
-typedef enum lru_status
-(*list_lru_walk_cb)(struct list_head *item, spinlock_t *lock, void *cb_arg);
+void list_lru_isolate(struct list_lru_one *list, struct list_head *item);
+void list_lru_isolate_move(struct list_lru_one *list, struct list_head *item,
+			   struct list_head *head);
+
+typedef enum lru_status (*list_lru_walk_cb)(struct list_head *item,
+		struct list_lru_one *list, spinlock_t *lock, void *cb_arg);
+
 /**
  * list_lru_walk_one: walk a list_lru, isolating and disposing freeable items.
  * @lru: the lru pointer.

mm/list_lru.c

@@ -132,6 +132,21 @@ bool list_lru_del(struct list_lru *lru, struct list_head *item)
 }
 EXPORT_SYMBOL_GPL(list_lru_del);
 
+void list_lru_isolate(struct list_lru_one *list, struct list_head *item)
+{
+	list_del_init(item);
+	list->nr_items--;
+}
+EXPORT_SYMBOL_GPL(list_lru_isolate);
+
+void list_lru_isolate_move(struct list_lru_one *list, struct list_head *item,
+			   struct list_head *head)
+{
+	list_move(item, head);
+	list->nr_items--;
+}
+EXPORT_SYMBOL_GPL(list_lru_isolate_move);
+
 static unsigned long __list_lru_count_one(struct list_lru *lru,
 					  int nid, int memcg_idx)
 {
@@ -194,13 +209,11 @@ restart:
 			break;
 		--*nr_to_walk;
 
-		ret = isolate(item, &nlru->lock, cb_arg);
+		ret = isolate(item, l, &nlru->lock, cb_arg);
 		switch (ret) {
 		case LRU_REMOVED_RETRY:
 			assert_spin_locked(&nlru->lock);
 		case LRU_REMOVED:
-			l->nr_items--;
-			WARN_ON_ONCE(l->nr_items < 0);
 			isolated++;
 			/*
 			 * If the lru lock has been dropped, our list

mm/workingset.c

@@ -302,6 +302,7 @@ static unsigned long count_shadow_nodes(struct shrinker *shrinker,
 }
 
 static enum lru_status shadow_lru_isolate(struct list_head *item,
+					  struct list_lru_one *lru,
 					  spinlock_t *lru_lock,
 					  void *arg)
 {
@@ -332,7 +333,7 @@ static enum lru_status shadow_lru_isolate(struct list_head *item,
 		goto out;
 	}
 
-	list_del_init(item);
+	list_lru_isolate(lru, item);
 	spin_unlock(lru_lock);
 
 	/*