[PATCH 3/5] zsmalloc: Add a LRU to zs_pool to keep track of zspages in LRU order

[Nhat Pham <nphamcs@gmail.com>]

This helps determines the coldest zspages as candidates for writeback.

Signed-off-by: Nhat Pham <nphamcs@gmail.com>
---
 mm/zsmalloc.c | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index 326faa751f0a..600c40121544 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -239,6 +239,9 @@ struct zs_pool {
 	/* Compact classes */
 	struct shrinker shrinker;
 
+	/* List tracking the zspages in LRU order by most recently added object */
+	struct list_head lru;
+
 #ifdef CONFIG_ZSMALLOC_STAT
 	struct dentry *stat_dentry;
 #endif
@@ -260,6 +263,10 @@ struct zspage {
 	unsigned int freeobj;
 	struct page *first_page;
 	struct list_head list; /* fullness list */
+
+	/* links the zspage to the lru list in the pool */
+	struct list_head lru;
+
 	struct zs_pool *pool;
 #ifdef CONFIG_COMPACTION
 	rwlock_t lock;
@@ -352,6 +359,16 @@ static void cache_free_zspage(struct zs_pool *pool, struct zspage *zspage)
 	kmem_cache_free(pool->zspage_cachep, zspage);
 }
 
+/* Moves the zspage to the front of the zspool's LRU */
+static void move_to_front(struct zs_pool *pool, struct zspage *zspage)
+{
+	assert_spin_locked(&pool->lock);
+
+	if (!list_empty(&zspage->lru))
+		list_del(&zspage->lru);
+	list_add(&zspage->lru, &pool->lru);
+}
+
 /* pool->lock(which owns the handle) synchronizes races */
 static void record_obj(unsigned long handle, unsigned long obj)
 {
@@ -953,6 +970,7 @@ static void free_zspage(struct zs_pool *pool, struct size_class *class,
 	}
 
 	remove_zspage(class, zspage, ZS_EMPTY);
+	list_del(&zspage->lru);
 	__free_zspage(pool, class, zspage);
 }
 
@@ -998,6 +1016,8 @@ static void init_zspage(struct size_class *class, struct zspage *zspage)
 		off %= PAGE_SIZE;
 	}
 
+	INIT_LIST_HEAD(&zspage->lru);
+
 	set_freeobj(zspage, 0);
 }
 
@@ -1418,6 +1438,8 @@ unsigned long zs_malloc(struct zs_pool *pool, size_t size, gfp_t gfp)
 		fix_fullness_group(class, zspage);
 		record_obj(handle, obj);
 		class_stat_inc(class, OBJ_USED, 1);
+		/* Move the zspage to front of pool's LRU */
+		move_to_front(pool, zspage);
 		spin_unlock(&pool->lock);
 
 		return handle;
@@ -1444,6 +1466,8 @@ unsigned long zs_malloc(struct zs_pool *pool, size_t size, gfp_t gfp)
 
 	/* We completely set up zspage so mark them as movable */
 	SetZsPageMovable(pool, zspage);
+	/* Move the zspage to front of pool's LRU */
+	move_to_front(pool, zspage);
 	spin_unlock(&pool->lock);
 
 	return handle;
@@ -1967,6 +1991,7 @@ static void async_free_zspage(struct work_struct *work)
 		VM_BUG_ON(fullness != ZS_EMPTY);
 		class = pool->size_class[class_idx];
 		spin_lock(&pool->lock);
+		list_del(&zspage->lru);
 		__free_zspage(pool, class, zspage);
 		spin_unlock(&pool->lock);
 	}
@@ -2278,6 +2303,8 @@ struct zs_pool *zs_create_pool(const char *name)
 	 */
 	zs_register_shrinker(pool);
 
+	INIT_LIST_HEAD(&pool->lru);
+
 	return pool;
 
 err:
-- 
2.30.2