From: NeilBrown neilb@suse.de
stable inclusion from linux-4.19.164 commit a5c43265c6244ce6df26b0c7a3d7f69449fb1a0a
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[ Upstream commit bf701b765eaa82dd164d65edc5747ec7288bb5c3 ]
nfsiod is currently a concurrency-managed workqueue (CMWQ). This means that workitems scheduled to nfsiod on a given CPU are queued behind all other work items queued on any CMWQ on the same CPU. This can introduce unexpected latency.
Occaionally nfsiod can even cause excessive latency. If the work item to complete a CLOSE request calls the final iput() on an inode, the address_space of that inode will be dismantled. This takes time proportional to the number of in-memory pages, which on a large host working on large files (e.g.. 5TB), can be a large number of pages resulting in a noticable number of seconds.
We can avoid these latency problems by switching nfsiod to WQ_UNBOUND. This causes each concurrent work item to gets a dedicated thread which can be scheduled to an idle CPU.
There is precedent for this as several other filesystems use WQ_UNBOUND workqueue for handling various async events.
Signed-off-by: NeilBrown neilb@suse.de Fixes: ada609ee2ac2 ("workqueue: use WQ_MEM_RECLAIM instead of WQ_RESCUER") Signed-off-by: Trond Myklebust trond.myklebust@hammerspace.com Signed-off-by: Sasha Levin sashal@kernel.org Signed-off-by: Yang Yingliang yangyingliang@huawei.com Signed-off-by: Cheng Jian cj.chengjian@huawei.com --- fs/nfs/inode.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/fs/nfs/inode.c b/fs/nfs/inode.c index 5d8e0eb0d663..905041eb24fe 100644 --- a/fs/nfs/inode.c +++ b/fs/nfs/inode.c @@ -2150,7 +2150,7 @@ static int nfsiod_start(void) { struct workqueue_struct *wq; dprintk("RPC: creating workqueue nfsiod\n"); - wq = alloc_workqueue("nfsiod", WQ_MEM_RECLAIM, 0); + wq = alloc_workqueue("nfsiod", WQ_MEM_RECLAIM | WQ_UNBOUND, 0); if (wq == NULL) return -ENOMEM; nfsiod_workqueue = wq;