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Date: Fri, 1 May 2015 03:17:37 -0700
From: Christoph Hellwig <hch@infradead.org>
To: Ming Lei <ming.lei@canonical.com>
Cc: Jens Axboe <axboe@kernel.dk>, linux-kernel@vger.kernel.org,
	"Justin M. Forbes" <jforbes@fedoraproject.org>,
	Jeff Moyer <jmoyer@redhat.com>,
	"v4.0" <stable@vger.kernel.org>, Tejun Heo <tj@kernel.org>
Subject: Re: [PATCH v6] block: loop: avoiding too many pending per work I/O
Message-ID: <20150501101737.GA18577@infradead.org>
References: <1430450881-10881-1-git-send-email-ming.lei@canonical.com>
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On Fri, May 01, 2015 at 11:28:01AM +0800, Ming Lei wrote:
> If there are too many pending per work I/O, too many
> high priority work thread can be generated so that
> system performance can be effected.
> 
> This patch limits the max pending per work I/O as 16,
> and will fackback to single queue mode when the max
> number is reached.

Why would you do this fall back?  Shouldn't we just communicate
a concurrency limit to the workqueue code?