Btrfs: Allow worker threads to exit when idle

The Btrfs worker threads don't currently die off after they have
been idle for a while, leading to a lot of threads sitting around
doing nothing for each mount.

Also, they are unable to start atomically (from end_io hanlders).

This commit reworks the worker threads so they can be started
from end_io handlers (just setting a flag that asks for a thread
to be added at a later date) and so they can exit if they
have been idle for a long time.

Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 12 insertions, 10 deletions

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 3cf4cfa575c8..20cefc6f22c4 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1682,7 +1682,7 @@ struct btrfs_root *open_ctree(struct super_block *sb,
                 err = -EINVAL;
                 goto fail_iput;
         }
-
+printk("thread pool is %d\n", fs_info->thread_pool_size);
         /*
          * we need to start all the end_io workers up front because the
          * queue work function gets called at interrupt time, and so it
@@ -1727,20 +1727,22 @@ struct btrfs_root *open_ctree(struct super_block *sb,
         fs_info->endio_workers.idle_thresh = 4;
         fs_info->endio_meta_workers.idle_thresh = 4;
 
-        fs_info->endio_write_workers.idle_thresh = 64;
-        fs_info->endio_meta_write_workers.idle_thresh = 64;
+        fs_info->endio_write_workers.idle_thresh = 2;
+        fs_info->endio_meta_write_workers.idle_thresh = 2;
+
+        fs_info->endio_workers.atomic_worker_start = 1;
+        fs_info->endio_meta_workers.atomic_worker_start = 1;
+        fs_info->endio_write_workers.atomic_worker_start = 1;
+        fs_info->endio_meta_write_workers.atomic_worker_start = 1;
 
         btrfs_start_workers(&fs_info->workers, 1);
         btrfs_start_workers(&fs_info->submit_workers, 1);
         btrfs_start_workers(&fs_info->delalloc_workers, 1);
         btrfs_start_workers(&fs_info->fixup_workers, 1);
-        btrfs_start_workers(&fs_info->endio_workers, fs_info->thread_pool_size);
-        btrfs_start_workers(&fs_info->endio_meta_workers,
-                            fs_info->thread_pool_size);
-        btrfs_start_workers(&fs_info->endio_meta_write_workers,
-                            fs_info->thread_pool_size);
-        btrfs_start_workers(&fs_info->endio_write_workers,
-                            fs_info->thread_pool_size);
+        btrfs_start_workers(&fs_info->endio_workers, 1);
+        btrfs_start_workers(&fs_info->endio_meta_workers, 1);
+        btrfs_start_workers(&fs_info->endio_meta_write_workers, 1);
+        btrfs_start_workers(&fs_info->endio_write_workers, 1);
 
         fs_info->bdi.ra_pages *= btrfs_super_num_devices(disk_super);
         fs_info->bdi.ra_pages = max(fs_info->bdi.ra_pages,