[RFC PATCH 3/6] zsmalloc: convert to sleepable pool lock

[Sergey Senozhatsky <senozhatsky@chromium.org>]

Switch over from rwlock_t to rwsemaphore, also introduce
simple helpers to lock/unlock the pool.  This is needed
to make zsmalloc preemptible in the future.

Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
---
 mm/zsmalloc.c | 58 ++++++++++++++++++++++++++++++++++++---------------
 1 file changed, 41 insertions(+), 17 deletions(-)

diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index 28a75bfbeaa6..751871ec533f 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -204,8 +204,8 @@ struct link_free {
 };
 
 struct zs_pool {
-	const char *name;
-
+	/* protect page/zspage migration */
+	struct rw_semaphore migrate_lock;
 	struct size_class *size_class[ZS_SIZE_CLASSES];
 	struct kmem_cache *handle_cachep;
 	struct kmem_cache *zspage_cachep;
@@ -216,6 +216,7 @@ struct zs_pool {
 
 	/* Compact classes */
 	struct shrinker *shrinker;
+	atomic_t compaction_in_progress;
 
 #ifdef CONFIG_ZSMALLOC_STAT
 	struct dentry *stat_dentry;
@@ -223,11 +224,34 @@ struct zs_pool {
 #ifdef CONFIG_COMPACTION
 	struct work_struct free_work;
 #endif
-	/* protect page/zspage migration */
-	rwlock_t migrate_lock;
-	atomic_t compaction_in_progress;
+	const char *name;
 };
 
+static void pool_write_unlock(struct zs_pool *pool)
+{
+	up_write(&pool->migrate_lock);
+}
+
+static void pool_write_lock(struct zs_pool *pool)
+{
+	down_write(&pool->migrate_lock);
+}
+
+static void pool_read_unlock(struct zs_pool *pool)
+{
+	up_read(&pool->migrate_lock);
+}
+
+static void pool_read_lock(struct zs_pool *pool)
+{
+	down_read(&pool->migrate_lock);
+}
+
+static bool zspool_lock_is_contended(struct zs_pool *pool)
+{
+	return rwsem_is_contended(&pool->migrate_lock);
+}
+
 static inline void zpdesc_set_first(struct zpdesc *zpdesc)
 {
 	SetPagePrivate(zpdesc_page(zpdesc));
@@ -1251,7 +1275,7 @@ void *zs_map_object(struct zs_pool *pool, unsigned long handle,
 	BUG_ON(in_interrupt());
 
 	/* It guarantees it can get zspage from handle safely */
-	read_lock(&pool->migrate_lock);
+	pool_read_lock(pool);
 	obj = handle_to_obj(handle);
 	obj_to_location(obj, &zpdesc, &obj_idx);
 	zspage = get_zspage(zpdesc);
@@ -1263,7 +1287,7 @@ void *zs_map_object(struct zs_pool *pool, unsigned long handle,
 	 * which is smaller granularity.
 	 */
 	zspage_read_lock(zspage);
-	read_unlock(&pool->migrate_lock);
+	pool_read_unlock(pool);
 
 	class = zspage_class(pool, zspage);
 	off = offset_in_page(class->size * obj_idx);
@@ -1498,13 +1522,13 @@ void zs_free(struct zs_pool *pool, unsigned long handle)
 	 * The pool->migrate_lock protects the race with zpage's migration
 	 * so it's safe to get the page from handle.
 	 */
-	read_lock(&pool->migrate_lock);
+	pool_read_lock(pool);
 	obj = handle_to_obj(handle);
 	obj_to_zpdesc(obj, &f_zpdesc);
 	zspage = get_zspage(f_zpdesc);
 	class = zspage_class(pool, zspage);
 	spin_lock(&class->lock);
-	read_unlock(&pool->migrate_lock);
+	pool_read_unlock(pool);
 
 	class_stat_sub(class, ZS_OBJS_INUSE, 1);
 	obj_free(class->size, obj);
@@ -1816,7 +1840,7 @@ static int zs_page_migrate(struct page *newpage, struct page *page,
 	 * The pool migrate_lock protects the race between zpage migration
 	 * and zs_free.
 	 */
-	write_lock(&pool->migrate_lock);
+	pool_write_lock(pool);
 	class = zspage_class(pool, zspage);
 
 	/*
@@ -1853,7 +1877,7 @@ static int zs_page_migrate(struct page *newpage, struct page *page,
 	 * Since we complete the data copy and set up new zspage structure,
 	 * it's okay to release migration_lock.
 	 */
-	write_unlock(&pool->migrate_lock);
+	pool_write_unlock(pool);
 	spin_unlock(&class->lock);
 	zspage_write_unlock(zspage);
 
@@ -1976,7 +2000,7 @@ static unsigned long __zs_compact(struct zs_pool *pool,
 	 * protect the race between zpage migration and zs_free
 	 * as well as zpage allocation/free
 	 */
-	write_lock(&pool->migrate_lock);
+	pool_write_lock(pool);
 	spin_lock(&class->lock);
 	while (zs_can_compact(class)) {
 		int fg;
@@ -2003,14 +2027,14 @@ static unsigned long __zs_compact(struct zs_pool *pool,
 		src_zspage = NULL;
 
 		if (get_fullness_group(class, dst_zspage) == ZS_INUSE_RATIO_100
-		    || rwlock_is_contended(&pool->migrate_lock)) {
+		    || zspool_lock_is_contended(pool)) {
 			putback_zspage(class, dst_zspage);
 			dst_zspage = NULL;
 
 			spin_unlock(&class->lock);
-			write_unlock(&pool->migrate_lock);
+			pool_write_unlock(pool);
 			cond_resched();
-			write_lock(&pool->migrate_lock);
+			pool_write_lock(pool);
 			spin_lock(&class->lock);
 		}
 	}
@@ -2022,7 +2046,7 @@ static unsigned long __zs_compact(struct zs_pool *pool,
 		putback_zspage(class, dst_zspage);
 
 	spin_unlock(&class->lock);
-	write_unlock(&pool->migrate_lock);
+	pool_write_unlock(pool);
 
 	return pages_freed;
 }
@@ -2159,7 +2183,7 @@ struct zs_pool *zs_create_pool(const char *name)
 		return NULL;
 
 	init_deferred_free(pool);
-	rwlock_init(&pool->migrate_lock);
+	init_rwsem(&pool->migrate_lock);
 	atomic_set(&pool->compaction_in_progress, 0);
 
 	pool->name = kstrdup(name, GFP_KERNEL);
-- 
2.48.1.262.g85cc9f2d1e-goog