Btrfs: compression: separate heuristic/compression workspaces

Compression heuristic itself is not a compression type, as current
infrastructure provides workspaces for several compression types, it's
difficult to just add heuristic workspace.

Just refactor the code to support compression/heuristic workspaces with
maximum code sharing and minimum changes in it.
Signed-off-by: Timofey Titovets <nefelim4ag@gmail.com>
Reviewed-by: David Sterba <dsterba@suse.com>
[ coding style fixes ]
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/compression.c

@@ -707,7 +707,34 @@ blk_status_t btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
 	return ret;
 }
 
-static struct {
+
+struct heuristic_ws {
+	struct list_head list;
+};
+
+static void free_heuristic_ws(struct list_head *ws)
+{
+	struct heuristic_ws *workspace;
+
+	workspace = list_entry(ws, struct heuristic_ws, list);
+
+	kfree(workspace);
+}
+
+static struct list_head *alloc_heuristic_ws(void)
+{
+	struct heuristic_ws *ws;
+
+	ws = kzalloc(sizeof(*ws), GFP_KERNEL);
+	if (!ws)
+		return ERR_PTR(-ENOMEM);
+
+	INIT_LIST_HEAD(&ws->list);
+
+	return &ws->list;
+}
+
+struct workspaces_list {
 	struct list_head idle_ws;
 	spinlock_t ws_lock;
 	/* Number of free workspaces */
@@ -716,7 +743,11 @@ static struct {
 	atomic_t total_ws;
 	/* Waiters for a free workspace */
 	wait_queue_head_t ws_wait;
-} btrfs_comp_ws[BTRFS_COMPRESS_TYPES];
+};
+
+static struct workspaces_list btrfs_comp_ws[BTRFS_COMPRESS_TYPES];
+
+static struct workspaces_list btrfs_heuristic_ws;
 
 static const struct btrfs_compress_op * const btrfs_compress_op[] = {
 	&btrfs_zlib_compress,
@@ -726,11 +757,25 @@ static const struct btrfs_compress_op * const btrfs_compress_op[] = {
 
 void __init btrfs_init_compress(void)
 {
+	struct list_head *workspace;
 	int i;
 
-	for (i = 0; i < BTRFS_COMPRESS_TYPES; i++) {
-		struct list_head *workspace;
+	INIT_LIST_HEAD(&btrfs_heuristic_ws.idle_ws);
+	spin_lock_init(&btrfs_heuristic_ws.ws_lock);
+	atomic_set(&btrfs_heuristic_ws.total_ws, 0);
+	init_waitqueue_head(&btrfs_heuristic_ws.ws_wait);
+
+	workspace = alloc_heuristic_ws();
+	if (IS_ERR(workspace)) {
+		pr_warn(
+	"BTRFS: cannot preallocate heuristic workspace, will try later\n");
+	} else {
+		atomic_set(&btrfs_heuristic_ws.total_ws, 1);
+		btrfs_heuristic_ws.free_ws = 1;
+		list_add(workspace, &btrfs_heuristic_ws.idle_ws);
+	}
 
+	for (i = 0; i < BTRFS_COMPRESS_TYPES; i++) {
 		INIT_LIST_HEAD(&btrfs_comp_ws[i].idle_ws);
 		spin_lock_init(&btrfs_comp_ws[i].ws_lock);
 		atomic_set(&btrfs_comp_ws[i].total_ws, 0);
@@ -757,18 +802,32 @@ void __init btrfs_init_compress(void)
  * Preallocation makes a forward progress guarantees and we do not return
  * errors.
  */
-static struct list_head *find_workspace(int type)
+static struct list_head *__find_workspace(int type, bool heuristic)
 {
 	struct list_head *workspace;
 	int cpus = num_online_cpus();
 	int idx = type - 1;
 	unsigned nofs_flag;
+	struct list_head *idle_ws;
+	spinlock_t *ws_lock;
+	atomic_t *total_ws;
+	wait_queue_head_t *ws_wait;
+	int *free_ws;
+
+	if (heuristic) {
+		idle_ws	 = &btrfs_heuristic_ws.idle_ws;
+		ws_lock	 = &btrfs_heuristic_ws.ws_lock;
+		total_ws = &btrfs_heuristic_ws.total_ws;
+		ws_wait	 = &btrfs_heuristic_ws.ws_wait;
+		free_ws	 = &btrfs_heuristic_ws.free_ws;
+	} else {
+		idle_ws	 = &btrfs_comp_ws[idx].idle_ws;
+		ws_lock	 = &btrfs_comp_ws[idx].ws_lock;
+		total_ws = &btrfs_comp_ws[idx].total_ws;
+		ws_wait	 = &btrfs_comp_ws[idx].ws_wait;
+		free_ws	 = &btrfs_comp_ws[idx].free_ws;
+	}
 
-	struct list_head *idle_ws	= &btrfs_comp_ws[idx].idle_ws;
-	spinlock_t *ws_lock		= &btrfs_comp_ws[idx].ws_lock;
-	atomic_t *total_ws		= &btrfs_comp_ws[idx].total_ws;
-	wait_queue_head_t *ws_wait	= &btrfs_comp_ws[idx].ws_wait;
-	int *free_ws			= &btrfs_comp_ws[idx].free_ws;
 again:
 	spin_lock(ws_lock);
 	if (!list_empty(idle_ws)) {
@@ -798,6 +857,9 @@ static struct list_head *find_workspace(int type)
 	 * context of btrfs_compress_bio/btrfs_compress_pages
 	 */
 	nofs_flag = memalloc_nofs_save();
+	if (heuristic)
+		workspace = alloc_heuristic_ws();
+	else
 		workspace = btrfs_compress_op[idx]->alloc_workspace();
 	memalloc_nofs_restore(nofs_flag);
 
@@ -829,18 +891,38 @@ static struct list_head *find_workspace(int type)
 	return workspace;
 }
 
+static struct list_head *find_workspace(int type)
+{
+	return __find_workspace(type, false);
+}
+
 /*
  * put a workspace struct back on the list or free it if we have enough
  * idle ones sitting around
  */
-static void free_workspace(int type, struct list_head *workspace)
+static void __free_workspace(int type, struct list_head *workspace,
+			     bool heuristic)
 {
 	int idx = type - 1;
-	struct list_head *idle_ws	= &btrfs_comp_ws[idx].idle_ws;
-	spinlock_t *ws_lock		= &btrfs_comp_ws[idx].ws_lock;
-	atomic_t *total_ws		= &btrfs_comp_ws[idx].total_ws;
-	wait_queue_head_t *ws_wait	= &btrfs_comp_ws[idx].ws_wait;
-	int *free_ws			= &btrfs_comp_ws[idx].free_ws;
+	struct list_head *idle_ws;
+	spinlock_t *ws_lock;
+	atomic_t *total_ws;
+	wait_queue_head_t *ws_wait;
+	int *free_ws;
+
+	if (heuristic) {
+		idle_ws	 = &btrfs_heuristic_ws.idle_ws;
+		ws_lock	 = &btrfs_heuristic_ws.ws_lock;
+		total_ws = &btrfs_heuristic_ws.total_ws;
+		ws_wait	 = &btrfs_heuristic_ws.ws_wait;
+		free_ws	 = &btrfs_heuristic_ws.free_ws;
+	} else {
+		idle_ws	 = &btrfs_comp_ws[idx].idle_ws;
+		ws_lock	 = &btrfs_comp_ws[idx].ws_lock;
+		total_ws = &btrfs_comp_ws[idx].total_ws;
+		ws_wait	 = &btrfs_comp_ws[idx].ws_wait;
+		free_ws	 = &btrfs_comp_ws[idx].free_ws;
+	}
 
 	spin_lock(ws_lock);
 	if (*free_ws <= num_online_cpus()) {
@@ -851,6 +933,9 @@ static void free_workspace(int type, struct list_head *workspace)
 	}
 	spin_unlock(ws_lock);
 
+	if (heuristic)
+		free_heuristic_ws(workspace);
+	else
 		btrfs_compress_op[idx]->free_workspace(workspace);
 	atomic_dec(total_ws);
 wake:
@@ -862,6 +947,11 @@ static void free_workspace(int type, struct list_head *workspace)
 		wake_up(ws_wait);
 }
 
+static void free_workspace(int type, struct list_head *ws)
+{
+	return __free_workspace(type, ws, false);
+}
+
 /*
  * cleanup function for module exit
  */
@@ -870,6 +960,13 @@ static void free_workspaces(void)
 	struct list_head *workspace;
 	int i;
 
+	while (!list_empty(&btrfs_heuristic_ws.idle_ws)) {
+		workspace = btrfs_heuristic_ws.idle_ws.next;
+		list_del(workspace);
+		free_heuristic_ws(workspace);
+		atomic_dec(&btrfs_heuristic_ws.total_ws);
+	}
+
 	for (i = 0; i < BTRFS_COMPRESS_TYPES; i++) {
 		while (!list_empty(&btrfs_comp_ws[i].idle_ws)) {
 			workspace = btrfs_comp_ws[i].idle_ws.next;
@@ -1090,11 +1187,15 @@ int btrfs_decompress_buf2page(const char *buf, unsigned long buf_start,
  */
 int btrfs_compress_heuristic(struct inode *inode, u64 start, u64 end)
 {
+	struct list_head *ws_list = __find_workspace(0, true);
+	struct heuristic_ws *ws;
 	u64 index = start >> PAGE_SHIFT;
 	u64 end_index = end >> PAGE_SHIFT;
 	struct page *page;
 	int ret = 1;
 
+	ws = list_entry(ws_list, struct heuristic_ws, list);
+
 	while (index <= end_index) {
 		page = find_get_page(inode->i_mapping, index);
 		kmap(page);
@@ -1103,6 +1204,8 @@ int btrfs_compress_heuristic(struct inode *inode, u64 start, u64 end)
 		index++;
 	}
 
+	__free_workspace(0, ws_list, true);
+
 	return ret;
 }