[PATCH v6 4/6] zsmalloc: Add a LRU to zs_pool to keep track of zspages in LRU order

[Nhat Pham <nphamcs@xxxxxxxxx>]

This helps determines the coldest zspages as candidates for writeback.

Signed-off-by: Nhat Pham <nphamcs@xxxxxxxxx>
---
 mm/zsmalloc.c | 34 ++++++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)

diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index 326faa751f0a..7dd464b5a6a5 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -239,6 +239,11 @@ struct zs_pool {
 	/* Compact classes */
 	struct shrinker shrinker;

+#ifdef CONFIG_ZPOOL
+	/* List tracking the zspages in LRU order by most recently added object */
+	struct list_head lru;
+#endif
+
 #ifdef CONFIG_ZSMALLOC_STAT
 	struct dentry *stat_dentry;
 #endif
@@ -260,6 +265,12 @@ struct zspage {
 	unsigned int freeobj;
 	struct page *first_page;
 	struct list_head list; /* fullness list */
+
+#ifdef CONFIG_ZPOOL
+	/* links the zspage to the lru list in the pool */
+	struct list_head lru;
+#endif
+
 	struct zs_pool *pool;
 #ifdef CONFIG_COMPACTION
 	rwlock_t lock;
@@ -953,6 +964,9 @@ static void free_zspage(struct zs_pool *pool, struct size_class *class,
 	}

 	remove_zspage(class, zspage, ZS_EMPTY);
+#ifdef CONFIG_ZPOOL
+	list_del(&zspage->lru);
+#endif
 	__free_zspage(pool, class, zspage);
 }

@@ -998,6 +1012,10 @@ static void init_zspage(struct size_class *class, struct zspage *zspage)
 		off %= PAGE_SIZE;
 	}

+#ifdef CONFIG_ZPOOL
+	INIT_LIST_HEAD(&zspage->lru);
+#endif
+
 	set_freeobj(zspage, 0);
 }

@@ -1249,6 +1267,15 @@ void *zs_map_object(struct zs_pool *pool, unsigned long handle,
 	obj_to_location(obj, &page, &obj_idx);
 	zspage = get_zspage(page);

+#ifdef CONFIG_ZPOOL
+	/* Move the zspage to front of pool's LRU */
+	if (mm == ZS_MM_WO) {
+		if (!list_empty(&zspage->lru))
+			list_del(&zspage->lru);
+		list_add(&zspage->lru, &pool->lru);
+	}
+#endif
+
 	/*
 	 * migration cannot move any zpages in this zspage. Here, pool->lock
 	 * is too heavy since callers would take some time until they calls
@@ -1967,6 +1994,9 @@ 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);
+#ifdef CONFIG_ZPOOL
+		list_del(&zspage->lru);
+#endif
 		__free_zspage(pool, class, zspage);
 		spin_unlock(&pool->lock);
 	}
@@ -2278,6 +2308,10 @@ struct zs_pool *zs_create_pool(const char *name)
 	 */
 	zs_register_shrinker(pool);

+#ifdef CONFIG_ZPOOL
+	INIT_LIST_HEAD(&pool->lru);
+#endif
+
 	return pool;

 err:
--
2.30.2