If you ever tried to implement unplug function in umem, you would find the code was almost identical as in dm/raid driver.
For other components which also need such unplug mechanism, it will much more convenient to have such facilities.
PS: What's your specific concern about blk_plug_cb handles each request_queue?

Thanks,
-Tao

-----Original Message-----
From: Shaohua Li [mailto:shlikernel@gmail.com] On Behalf Of Shaohua Li
Sent: Tuesday, June 05, 2012 9:21 AM
To: Tao Guo
Cc: linux-kernel@vger.kernel.org; Guo, Tao; Neil Brown; Jens Axboe;
stable@vger.kernel.org; Andrew Morton
Subject: Re: [PATCH 1/2] block: Move general unplug callback function
from md/raid to blk-core

On Mon, Jun 04, 2012 at 10:41:50AM -0400, Tao Guo wrote:

quoted

Other components may also require an unplug callback, so move this
function from md/raid to block generic layer.

I saw no point this should be generic code, for example, why
blk_plug_cb only
handles only one request_queue? If umem needs unplug, just do in it.