This is a note to let you know that I've just added the patch titled Revert "bcache: Kill btree_io_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: revert-bcache-kill-btree_io_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 9f233ffe02e5cef611100cd8c5bcf4de26ca7bef Mon Sep 17 00:00:00 2001 From: Kai Krakow <kai@xxxxxxxxxxx> Date: Wed, 10 Feb 2021 13:07:25 +0800 Subject: Revert "bcache: Kill btree_io_wq" From: Kai Krakow <kai@xxxxxxxxxxx> commit 9f233ffe02e5cef611100cd8c5bcf4de26ca7bef upstream. This reverts commit 56b30770b27d54d68ad51eccc6d888282b568cee. With the btree using the `system_wq`, I seem to see a lot more desktop latency than I should. After some more investigation, it looks like the original assumption of 56b3077 no longer is true, and bcache has a very high potential of congesting the `system_wq`. In turn, this introduces laggy desktop performance, IO stalls (at least with btrfs), and input events may be delayed. So let's revert this. It's important to note that the semantics of using `system_wq` previously mean that `btree_io_wq` should be created before and destroyed after other bcache wqs to keep the same assumptions. 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 | 2 ++ drivers/md/bcache/btree.c | 21 +++++++++++++++++++-- drivers/md/bcache/super.c | 4 ++++ 3 files changed, 25 insertions(+), 2 deletions(-) --- a/drivers/md/bcache/bcache.h +++ b/drivers/md/bcache/bcache.h @@ -1042,5 +1042,7 @@ void bch_debug_exit(void); void bch_debug_init(void); void bch_request_exit(void); int bch_request_init(void); +void bch_btree_exit(void); +int bch_btree_init(void); #endif /* _BCACHE_H */ --- a/drivers/md/bcache/btree.c +++ b/drivers/md/bcache/btree.c @@ -99,6 +99,8 @@ #define PTR_HASH(c, k) \ (((k)->ptr[0] >> c->bucket_bits) | PTR_GEN(k, 0)) +static struct workqueue_struct *btree_io_wq; + #define insert_lock(s, b) ((b)->level <= (s)->lock) @@ -308,7 +310,7 @@ static void __btree_node_write_done(stru btree_complete_write(b, w); if (btree_node_dirty(b)) - schedule_delayed_work(&b->work, 30 * HZ); + queue_delayed_work(btree_io_wq, &b->work, 30 * HZ); closure_return_with_destructor(cl, btree_node_write_unlock); } @@ -481,7 +483,7 @@ static void bch_btree_leaf_dirty(struct BUG_ON(!i->keys); if (!btree_node_dirty(b)) - schedule_delayed_work(&b->work, 30 * HZ); + queue_delayed_work(btree_io_wq, &b->work, 30 * HZ); set_btree_node_dirty(b); @@ -2764,3 +2766,18 @@ void bch_keybuf_init(struct keybuf *buf) spin_lock_init(&buf->lock); array_allocator_init(&buf->freelist); } + +void bch_btree_exit(void) +{ + if (btree_io_wq) + destroy_workqueue(btree_io_wq); +} + +int __init bch_btree_init(void) +{ + btree_io_wq = create_singlethread_workqueue("bch_btree_io"); + if (!btree_io_wq) + return -ENOMEM; + + return 0; +} --- a/drivers/md/bcache/super.c +++ b/drivers/md/bcache/super.c @@ -2821,6 +2821,7 @@ static void bcache_exit(void) destroy_workqueue(bcache_wq); if (bch_journal_wq) destroy_workqueue(bch_journal_wq); + bch_btree_exit(); if (bcache_major) unregister_blkdev(bcache_major, "bcache"); @@ -2876,6 +2877,9 @@ static int __init bcache_init(void) return bcache_major; } + if (bch_btree_init()) + goto err; + bcache_wq = alloc_workqueue("bcache", WQ_MEM_RECLAIM, 0); if (!bcache_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