linux-kernel - Re: [PATCH] writeback: account BDI's min

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Message-ID: <20150817195805.GE21075@mtj.duckdns.org>
Date:	Mon, 17 Aug 2015 15:58:05 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Akinobu Mita <akinobu.mita@...il.com>
Cc:	linux-kernel@...r.kernel.org, Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCH] writeback: account BDI's min_ratio for unregistered
 device

On Mon, Aug 17, 2015 at 11:45:53PM +0900, Akinobu Mita wrote:
> From mm/page-writeback.c:
> 
> 	/*
> 	 * bdi_min_ratio keeps the sum of the minimum dirty shares of all
> 	 * registered backing devices, which, for obvious reasons, can not
> 	 * exceed 100%.
> 	 */
> 	static unsigned int bdi_min_ratio;
> 
> But when a backing device is unregistered, the BDI's min_ratio is not
> subtracted from bdi_min_ratio.  So the second attempt to set min_ratio
> in the following commands will fail.
> 
> 	# modprobe null_blk
> 	# echo 50 > /sys/block/nullb0/bdi/min_ratio
> 	# modprobe -r null_blk
> 	# modprobe null_blk
> 	# echo 50 > /sys/block/nullb0/bdi/min_ratio
> 
> Signed-off-by: Akinobu Mita <akinobu.mita@...il.com>
> Cc: Tejun Heo <tj@...nel.org>
> Cc: Jens Axboe <axboe@...nel.dk>

Acked-by: Tejun Heo <tj@...nel.org>

We probably want to cc stable too.

Thanks.

-- 
tejun
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