From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Zijlstra Subject: Re: [PATCH 2/5] writeback: dirty position control Date: Tue, 09 Aug 2011 12:32:19 +0200 Message-ID: <1312885939.22367.73.camel@twins> References: <20110806084447.388624428@intel.com> <20110806094526.733282037@intel.com> <1312811193.10488.33.camel@twins> <20110808141128.GA22080@localhost> <1312814501.10488.41.camel@twins> <20110808230535.GC7176@localhost> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Cc: "linux-fsdevel@vger.kernel.org" , Andrew Morton , Jan Kara , Christoph Hellwig , Dave Chinner , Greg Thelen , Minchan Kim , Vivek Goyal , Andrea Righi , linux-mm , LKML To: Wu Fengguang Return-path: In-Reply-To: <20110808230535.GC7176@localhost> Sender: owner-linux-mm@kvack.org List-Id: linux-fsdevel.vger.kernel.org On Tue, 2011-08-09 at 07:05 +0800, Wu Fengguang wrote: > This is the more meaningful view :) >=20 > origin - dirty > pos_ratio =3D -------------- > origin - goal=20 > which comes from the below [*] control line, so that when (dirty =3D=3D g= oal), > pos_ratio =3D=3D 1.0: OK, so basically you want a linear function for which: f(goal) =3D 1 and has a root somewhere > goal. (that one line is much more informative than all your graphs put together, one can start from there and derive your function) That does indeed get you the above function, now what does it mean? > + * When the number of dirty pages go higher/lower than the setpoint, th= e dirty > + * position ratio (and hence dirty rate limit) will be decreased/increa= sed to > + * bring the dirty pages back to the setpoint. (you seem inconsistent with your terminology, I think goal and setpoint are interchanged? I looked up set point and its a term from control system theory, so I'll chalk that up to my own ignorance..) Ok, so higher dirty -> lower position ration -> lower dirty rate (and the inverse), now what does that do... /me goes read other patches in search of more clues.. I'm starting to dislike graphs.. why not simply state where those things come from, that's much easier. -- 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 internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org