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From: Josef Bacik <josef@toxicpanda.com>
To: Xie Yongji <xieyongji@bytedance.com>
Cc: axboe@kernel.dk, bvanassche@acm.org, linux-block@vger.kernel.org,
	nbd@other.debian.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] nbd: Don't use workqueue to handle recv work
Date: Tue, 22 Mar 2022 16:11:38 -0400	[thread overview]
Message-ID: <YjotekJZcSvwoZhp@localhost.localdomain> (raw)
In-Reply-To: <20211227091241.103-1-xieyongji@bytedance.com>

On Mon, Dec 27, 2021 at 05:12:41PM +0800, Xie Yongji wrote:
> The rescuer thread might take over the works queued on
> the workqueue when the worker thread creation timed out.
> If this happens, we have no chance to create multiple
> recv threads which causes I/O hung on this nbd device.
> 
> To fix it, we can not simply remove the WQ_MEM_RECLAIM
> flag since the recv work is in the memory reclaim path.
> So this patch tries to create kthreads directly to
> handle the recv work instead of using workqueue.
> 

I still don't understand why we can't drop WQ_MEM_RECLAIM.  IIRC your argument
is that we need it because a reconnect could happen under memory pressure and we
need to be able to queue work for that.  However your code makes it so we're
just doing a kthread_create(), which isn't coming out of some emergency pool, so
it's just as likely to fail as a !WQ_MEM_RECLAIM workqueue.  Thanks,

Josef

  parent reply	other threads:[~2022-03-22 20:11 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-12-27  9:12 [PATCH v2] nbd: Don't use workqueue to handle recv work Xie Yongji
2021-12-29 17:35 ` Christoph Hellwig
2021-12-30  4:01   ` Yongji Xie
2022-01-03 16:10     ` Josef Bacik
2022-01-04  5:31       ` Yongji Xie
2022-01-04 18:06         ` Josef Bacik
2022-01-05  5:36           ` Yongji Xie
2022-01-21  8:34             ` Yongji Xie
2022-02-15 13:17               ` Yongji Xie
2022-02-18 15:20                 ` Josef Bacik
2022-02-19 13:04                   ` Yongji Xie
2022-03-22  8:10                     ` Yongji Xie
2022-03-22 20:11 ` Josef Bacik [this message]
2022-03-23 11:21   ` Yongji Xie
2022-05-16  6:13     ` Yongji Xie

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