Btrfs: set ioprio of scrub readahead to idle

Reduce ioprio class of scrub readahead threads to idle priority.
This setting is fixed. This priority has shown the best performance
during all measurements.

Signed-off-by: Stefan Behrens <sbehrens@giantdisaster.de>

2 files changed, 8 insertions, 0 deletions

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index e176f8c551f7..1c665ebe47e0 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -173,6 +173,9 @@ static int btrfs_csum_sizes[] = { 4, 0 };
 #define BTRFS_FT_XATTR          8
 #define BTRFS_FT_MAX            9
 
+/* ioprio of readahead is set to idle */
+#define BTRFS_IOPRIO_READA (IOPRIO_PRIO_VALUE(IOPRIO_CLASS_IDLE, 0))
+
 /*
  * The key defines the order in the tree, and so it also defines (optimal)
  * block layout.
diff --git a/fs/btrfs/reada.c b/fs/btrfs/reada.c
index ac5d01085884..48a4882d8ad5 100644
--- a/fs/btrfs/reada.c
+++ b/fs/btrfs/reada.c
@@ -718,13 +718,18 @@ static void reada_start_machine_worker(struct btrfs_work *work)
 {
         struct reada_machine_work *rmw;
         struct btrfs_fs_info *fs_info;
+        int old_ioprio;
 
         rmw = container_of(work, struct reada_machine_work, work);
         fs_info = rmw->fs_info;
 
         kfree(rmw);
 
+        old_ioprio = IOPRIO_PRIO_VALUE(task_nice_ioclass(current),
+                                       task_nice_ioprio(current));
+        set_task_ioprio(current, BTRFS_IOPRIO_READA);
         __reada_start_machine(fs_info);
+        set_task_ioprio(current, old_ioprio);
 }
 
 static void __reada_start_machine(struct btrfs_fs_info *fs_info)