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>
diff --git a/fs/btrfs/async-thread.c b/fs/btrfs/async-thread.c
index 019e8af..f10c895 100644
--- a/fs/btrfs/async-thread.c
+++ b/fs/btrfs/async-thread.c
@@ -48,6 +48,9 @@
/* number of things on the pending list */
atomic_t num_pending;
+ /* reference counter for this struct */
+ atomic_t refs;
+
unsigned long sequence;
/* protects the pending list. */
@@ -93,6 +96,31 @@
}
}
+static void check_pending_worker_creates(struct btrfs_worker_thread *worker)
+{
+ struct btrfs_workers *workers = worker->workers;
+ unsigned long flags;
+
+ rmb();
+ if (!workers->atomic_start_pending)
+ return;
+
+ spin_lock_irqsave(&workers->lock, flags);
+ if (!workers->atomic_start_pending)
+ goto out;
+
+ workers->atomic_start_pending = 0;
+ if (workers->num_workers >= workers->max_workers)
+ goto out;
+
+ spin_unlock_irqrestore(&workers->lock, flags);
+ btrfs_start_workers(workers, 1);
+ return;
+
+out:
+ spin_unlock_irqrestore(&workers->lock, flags);
+}
+
static noinline int run_ordered_completions(struct btrfs_workers *workers,
struct btrfs_work *work)
{
@@ -140,6 +168,36 @@
return 0;
}
+static void put_worker(struct btrfs_worker_thread *worker)
+{
+ if (atomic_dec_and_test(&worker->refs))
+ kfree(worker);
+}
+
+static int try_worker_shutdown(struct btrfs_worker_thread *worker)
+{
+ int freeit = 0;
+
+ spin_lock_irq(&worker->lock);
+ spin_lock_irq(&worker->workers->lock);
+ if (worker->workers->num_workers > 1 &&
+ worker->idle &&
+ !worker->working &&
+ !list_empty(&worker->worker_list) &&
+ list_empty(&worker->prio_pending) &&
+ list_empty(&worker->pending)) {
+ freeit = 1;
+ list_del_init(&worker->worker_list);
+ worker->workers->num_workers--;
+ }
+ spin_unlock_irq(&worker->workers->lock);
+ spin_unlock_irq(&worker->lock);
+
+ if (freeit)
+ put_worker(worker);
+ return freeit;
+}
+
/*
* main loop for servicing work items
*/
@@ -175,6 +233,8 @@
*/
run_ordered_completions(worker->workers, work);
+ check_pending_worker_creates(worker);
+
spin_lock_irq(&worker->lock);
check_idle_worker(worker);
}
@@ -226,8 +286,13 @@
worker->working = 0;
spin_unlock_irq(&worker->lock);
- if (!kthread_should_stop())
- schedule();
+ if (!kthread_should_stop()) {
+ schedule_timeout(HZ * 120);
+ if (!worker->working &&
+ try_worker_shutdown(worker)) {
+ return 0;
+ }
+ }
}
__set_current_state(TASK_RUNNING);
}
@@ -242,16 +307,30 @@
{
struct list_head *cur;
struct btrfs_worker_thread *worker;
+ int can_stop;
+ spin_lock_irq(&workers->lock);
list_splice_init(&workers->idle_list, &workers->worker_list);
while (!list_empty(&workers->worker_list)) {
cur = workers->worker_list.next;
worker = list_entry(cur, struct btrfs_worker_thread,
worker_list);
- kthread_stop(worker->task);
- list_del(&worker->worker_list);
- kfree(worker);
+
+ atomic_inc(&worker->refs);
+ workers->num_workers -= 1;
+ if (!list_empty(&worker->worker_list)) {
+ list_del_init(&worker->worker_list);
+ put_worker(worker);
+ can_stop = 1;
+ } else
+ can_stop = 0;
+ spin_unlock_irq(&workers->lock);
+ if (can_stop)
+ kthread_stop(worker->task);
+ spin_lock_irq(&workers->lock);
+ put_worker(worker);
}
+ spin_unlock_irq(&workers->lock);
return 0;
}
@@ -270,6 +349,8 @@
workers->idle_thresh = 32;
workers->name = name;
workers->ordered = 0;
+ workers->atomic_start_pending = 0;
+ workers->atomic_worker_start = 0;
}
/*
@@ -294,6 +375,7 @@
INIT_LIST_HEAD(&worker->worker_list);
spin_lock_init(&worker->lock);
atomic_set(&worker->num_pending, 0);
+ atomic_set(&worker->refs, 1);
worker->workers = workers;
worker->task = kthread_run(worker_loop, worker,
"btrfs-%s-%d", workers->name,
@@ -303,7 +385,6 @@
kfree(worker);
goto fail;
}
-
spin_lock_irq(&workers->lock);
list_add_tail(&worker->worker_list, &workers->idle_list);
worker->idle = 1;
@@ -367,6 +448,7 @@
{
struct btrfs_worker_thread *worker;
unsigned long flags;
+ struct list_head *fallback;
again:
spin_lock_irqsave(&workers->lock, flags);
@@ -376,19 +458,10 @@
if (!worker) {
spin_lock_irqsave(&workers->lock, flags);
if (workers->num_workers >= workers->max_workers) {
- struct list_head *fallback = NULL;
- /*
- * we have failed to find any workers, just
- * return the force one
- */
- if (!list_empty(&workers->worker_list))
- fallback = workers->worker_list.next;
- if (!list_empty(&workers->idle_list))
- fallback = workers->idle_list.next;
- BUG_ON(!fallback);
- worker = list_entry(fallback,
- struct btrfs_worker_thread, worker_list);
- spin_unlock_irqrestore(&workers->lock, flags);
+ goto fallback;
+ } else if (workers->atomic_worker_start) {
+ workers->atomic_start_pending = 1;
+ goto fallback;
} else {
spin_unlock_irqrestore(&workers->lock, flags);
/* we're below the limit, start another worker */
@@ -397,6 +470,22 @@
}
}
return worker;
+
+fallback:
+ fallback = NULL;
+ /*
+ * we have failed to find any workers, just
+ * return the first one we can find.
+ */
+ if (!list_empty(&workers->worker_list))
+ fallback = workers->worker_list.next;
+ if (!list_empty(&workers->idle_list))
+ fallback = workers->idle_list.next;
+ BUG_ON(!fallback);
+ worker = list_entry(fallback,
+ struct btrfs_worker_thread, worker_list);
+ spin_unlock_irqrestore(&workers->lock, flags);
+ return worker;
}
/*
@@ -435,9 +524,9 @@
worker->working = 1;
}
- spin_unlock_irqrestore(&worker->lock, flags);
if (wake)
wake_up_process(worker->task);
+ spin_unlock_irqrestore(&worker->lock, flags);
out:
return 0;
@@ -492,10 +581,10 @@
wake = 1;
worker->working = 1;
- spin_unlock_irqrestore(&worker->lock, flags);
-
if (wake)
wake_up_process(worker->task);
+ spin_unlock_irqrestore(&worker->lock, flags);
+
out:
return 0;
}
diff --git a/fs/btrfs/async-thread.h b/fs/btrfs/async-thread.h
index 1b511c1..a562ad8 100644
--- a/fs/btrfs/async-thread.h
+++ b/fs/btrfs/async-thread.h
@@ -73,6 +73,15 @@
/* force completions in the order they were queued */
int ordered;
+ /* more workers required, but in an interrupt handler */
+ int atomic_start_pending;
+
+ /*
+ * are we allowed to sleep while starting workers or are we required
+ * to start them at a later time?
+ */
+ int atomic_worker_start;
+
/* list with all the work threads. The workers on the idle thread
* may be actively servicing jobs, but they haven't yet hit the
* idle thresh limit above.
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 3cf4cfa..20cefc6 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1682,7 +1682,7 @@
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 @@
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,
