[PATCH 2/2] bcachefs: set rebalance thread to SCHED_BATCH and nice 19

[Florian Schmaus]

While the rebalance thread is isually not compute bound, it does cause
a considerable amount of I/O. Since "reducing" the nice level from 0
to 19, also implicitly reduces the threads best-effort I/O scheduling
class level from 4 to 7, the reblance thread's I/O will be depriotized
over normal I/O.

Furthermore, we set the rebalance thread's scheduling class to BATCH,
which means that it will potentially receive a higher scheduling
latency. Making room for threads that need a low
schedulinglatency (e.g., interactive onces).

Signed-off-by: Florian Schmaus <flo@xxxxxxxxxxxx>
---
 fs/bcachefs/rebalance.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/bcachefs/rebalance.c b/fs/bcachefs/rebalance.c
index cd6647374353..87e4f507af80 100644
--- a/fs/bcachefs/rebalance.c
+++ b/fs/bcachefs/rebalance.c
@@ -22,6 +22,7 @@
 
 #include <linux/freezer.h>
 #include <linux/kthread.h>
+#include <linux/sched.h>
 #include <linux/sched/cputime.h>
 
 #define REBALANCE_WORK_SCAN_OFFSET	(U64_MAX - 1)
@@ -478,6 +479,8 @@ int bch2_rebalance_start(struct bch_fs *c)
 	if (ret)
 		return ret;
 
+	sched_set_batch(p, 19);
+
 	get_task_struct(p);
 	rcu_assign_pointer(c->rebalance.thread, p);
 	wake_up_process(p);
-- 
2.45.2