btrfs: reada: limit max works count

Reada creates 2 works for each level of tree recursively.

In case of a tree having many levels, the number of created works
is 2^level_of_tree.
Actually we don't need so many works in parallel, this patch limits
max works to BTRFS_MAX_MIRRORS * 2.

The per-fs works_counter will be also used for btrfs_reada_wait() to
check is there are background workers.

Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.com>

3 files changed, 12 insertions, 1 deletions

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index e557e05d2318..e43d987e1c99 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -1822,6 +1822,9 @@ struct btrfs_fs_info {
         spinlock_t reada_lock;
         struct radix_tree_root reada_tree;
 
+        /* readahead works cnt */
+        atomic_t reada_works_cnt;
+
         /* Extent buffer radix tree */
         spinlock_t buffer_lock;
         struct radix_tree_root buffer_radix;
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 498156ede32c..5e3ec1fc0ac3 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -2603,6 +2603,7 @@ int open_ctree(struct super_block *sb,
         atomic_set(&fs_info->nr_async_bios, 0);
         atomic_set(&fs_info->defrag_running, 0);
         atomic_set(&fs_info->qgroup_op_seq, 0);
+        atomic_set(&fs_info->reada_works_cnt, 0);
         atomic64_set(&fs_info->tree_mod_seq, 0);
         fs_info->sb = sb;
         fs_info->max_inline = BTRFS_DEFAULT_MAX_INLINE;
diff --git a/fs/btrfs/reada.c b/fs/btrfs/reada.c
index 9157d789ae86..e97bc8eb01e2 100644
--- a/fs/btrfs/reada.c
+++ b/fs/btrfs/reada.c
@@ -748,6 +748,8 @@ static void reada_start_machine_worker(struct btrfs_work *work)
         set_task_ioprio(current, BTRFS_IOPRIO_READA);
         __reada_start_machine(fs_info);
         set_task_ioprio(current, old_ioprio);
+
+        atomic_dec(&fs_info->reada_works_cnt);
 }
 
 static void __reada_start_machine(struct btrfs_fs_info *fs_info)
@@ -779,8 +781,12 @@ static void __reada_start_machine(struct btrfs_fs_info *fs_info)
          * enqueue to workers to finish it. This will distribute the load to
          * the cores.
          */
-        for (i = 0; i < 2; ++i)
+        for (i = 0; i < 2; ++i) {
                 reada_start_machine(fs_info);
+                if (atomic_read(&fs_info->reada_works_cnt) >
+                    BTRFS_MAX_MIRRORS * 2)
+                        break;
+        }
 }
 
 static void reada_start_machine(struct btrfs_fs_info *fs_info)
@@ -797,6 +803,7 @@ static void reada_start_machine(struct btrfs_fs_info *fs_info)
         rmw->fs_info = fs_info;
 
         btrfs_queue_work(fs_info->readahead_workers, &rmw->work);
+        atomic_inc(&fs_info->reada_works_cnt);
 }
 
 #ifdef DEBUG