This is a note to let you know that I've just added the patch titled
bcache: Move journal work to new flush wq
to the 5.11-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
bcache-move-journal-work-to-new-flush-wq.patch
and it can be found in the queue-5.11 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From afe78ab46f638ecdf80a35b122ffc92c20d9ae5d Mon Sep 17 00:00:00 2001
From: Kai Krakow <kai@xxxxxxxxxxx>
Date: Wed, 10 Feb 2021 13:07:27 +0800
Subject: bcache: Move journal work to new flush wq
From: Kai Krakow <kai@xxxxxxxxxxx>
commit afe78ab46f638ecdf80a35b122ffc92c20d9ae5d upstream.
This is potentially long running and not latency sensitive, let's get
it out of the way of other latency sensitive events.
As observed in the previous commit, the `system_wq` comes easily
congested by bcache, and this fixes a few more stalls I was observing
every once in a while.
Let's not make this `WQ_MEM_RECLAIM` as it showed to reduce performance
of boot and file system operations in my tests. Also, without
`WQ_MEM_RECLAIM`, I no longer see desktop stalls. This matches the
previous behavior as `system_wq` also does no memory reclaim:
> // workqueue.c:
> system_wq = alloc_workqueue("events", 0, 0);
Cc: Coly Li <colyli@xxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx # 5.4+
Signed-off-by: Kai Krakow <kai@xxxxxxxxxxx>
Signed-off-by: Coly Li <colyli@xxxxxxx>
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/md/bcache/bcache.h | 1 +
drivers/md/bcache/journal.c | 4 ++--
drivers/md/bcache/super.c | 16 ++++++++++++++++
3 files changed, 19 insertions(+), 2 deletions(-)
--- a/drivers/md/bcache/bcache.h
+++ b/drivers/md/bcache/bcache.h
@@ -1001,6 +1001,7 @@ void bch_write_bdev_super(struct cached_
extern struct workqueue_struct *bcache_wq;
extern struct workqueue_struct *bch_journal_wq;
+extern struct workqueue_struct *bch_flush_wq;
extern struct mutex bch_register_lock;
extern struct list_head bch_cache_sets;
--- a/drivers/md/bcache/journal.c
+++ b/drivers/md/bcache/journal.c
@@ -932,8 +932,8 @@ atomic_t *bch_journal(struct cache_set *
journal_try_write(c);
} else if (!w->dirty) {
w->dirty = true;
- schedule_delayed_work(&c->journal.work,
- msecs_to_jiffies(c->journal_delay_ms));
+ queue_delayed_work(bch_flush_wq, &c->journal.work,
+ msecs_to_jiffies(c->journal_delay_ms));
spin_unlock(&c->journal.lock);
} else {
spin_unlock(&c->journal.lock);
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -49,6 +49,7 @@ static int bcache_major;
static DEFINE_IDA(bcache_device_idx);
static wait_queue_head_t unregister_wait;
struct workqueue_struct *bcache_wq;
+struct workqueue_struct *bch_flush_wq;
struct workqueue_struct *bch_journal_wq;
@@ -2821,6 +2822,8 @@ static void bcache_exit(void)
destroy_workqueue(bcache_wq);
if (bch_journal_wq)
destroy_workqueue(bch_journal_wq);
+ if (bch_flush_wq)
+ destroy_workqueue(bch_flush_wq);
bch_btree_exit();
if (bcache_major)
@@ -2884,6 +2887,19 @@ static int __init bcache_init(void)
if (!bcache_wq)
goto err;
+ /*
+ * Let's not make this `WQ_MEM_RECLAIM` for the following reasons:
+ *
+ * 1. It used `system_wq` before which also does no memory reclaim.
+ * 2. With `WQ_MEM_RECLAIM` desktop stalls, increased boot times, and
+ * reduced throughput can be observed.
+ *
+ * We still want to user our own queue to not congest the `system_wq`.
+ */
+ bch_flush_wq = alloc_workqueue("bch_flush", 0, 0);
+ if (!bch_flush_wq)
+ goto err;
+
bch_journal_wq = alloc_workqueue("bch_journal", WQ_MEM_RECLAIM, 0);
if (!bch_journal_wq)
goto err;
Patches currently in stable-queue which might be from kai@xxxxxxxxxxx are
queue-5.11/revert-bcache-kill-btree_io_wq.patch
queue-5.11/bcache-give-btree_io_wq-correct-semantics-again.patch
queue-5.11/bcache-move-journal-work-to-new-flush-wq.patch
