From mboxrd@z Thu Jan 1 00:00:00 1970 From: Rik van Riel Subject: Re: [PATCH] writeback: enabling-gate for light dirtied bdi Date: Sun, 05 Dec 2010 09:04:17 -0500 Message-ID: <4CFB9BE1.3030902@redhat.com> References: <20101205064430.GA15027@localhost> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: Peter Zijlstra , Andrew Morton , "Theodore Ts'o" , Chris Mason , Dave Chinner , Jan Kara , Jens Axboe , Mel Gorman , KOSAKI Motohiro , Christoph Hellwig , linux-mm , "linux-fsdevel@vger.kernel.org" , LKML To: Wu Fengguang Return-path: In-Reply-To: <20101205064430.GA15027@localhost> Sender: owner-linux-mm@kvack.org List-Id: linux-fsdevel.vger.kernel.org On 12/05/2010 01:44 AM, Wu Fengguang wrote: > I noticed that my NFSROOT test system goes slow responding when there > is heavy dd to a local disk. Traces show that the NFSROOT's bdi_limit > is near 0 and many tasks in the system are repeatedly stuck in > balance_dirty_pages(). > > There are two related problems: > > - light dirtiers at one device (more often than not the rootfs) get > heavily impacted by heavy dirtiers on another independent device > > - the light dirtied device does heavy throttling because bdi_limit=0, > and the heavy throttling may in turn withhold its bdi_limit in 0 as > it cannot dirty fast enough to grow up the bdi's proportional weight. > > Fix it by introducing some "low pass" gate, which is a small (<=8MB) > value reserved by others and can be safely "stole" from the current > global dirty margin. It does not need to be big to help the bdi gain > its initial weight. Makes a lot of sense to me. Acked-by: Rik van Riel -- All rights reversed -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: email@kvack.org