linux-kernel - Re: [PATCH 2/5] writeback: dirty position control

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20110812031806.GA26495@localhost>
Date:	Fri, 12 Aug 2011 11:18:06 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jan Kara <jack@...e.cz>, Christoph Hellwig <hch@....de>,
	Dave Chinner <david@...morbit.com>,
	Greg Thelen <gthelen@...gle.com>,
	Minchan Kim <minchan.kim@...il.com>,
	Vivek Goyal <vgoyal@...hat.com>,
	Andrea Righi <arighi@...eler.com>,
	linux-mm <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/5] writeback: dirty position control

Sorry forgot the 2 gnuplot figures, attached now.

> > Making our final function look like:
> > 
> >                s - x 3
> >  f(x) :=  1 + (-----)
> >                l - s
> 
> Very intuitive reasoning, thanks!
> 
> I substituted real numbers to the function assuming a mem=2GB system.
> 
> with limit=thresh:
> 
>         gnuplot> set xrange [60000:80000]
>         gnuplot> plot 1 +  (70000.0 - x)**3/(80000-70000.0)**3
> 
> with limit=thresh+thresh/DIRTY_SCOPE
> 
>         gnuplot> set xrange [60000:90000]
>         gnuplot> plot 1 +  (70000.0 - x)**3/(90000-70000.0)**3
> 
> Figures attached.  The latter produces reasonably flat slope and I'll
> give it a spin in the dd tests :)
>  
> > You can clamp it at [0,2] or so.
> 
> Looking at the figures, we may even do without the clamp because it's
> already inside the range [0, 2].
> 
> > The implementation wouldn't be too horrid either, something like:
> > 
> > unsigned long bdi_pos_ratio(..)
> > {
> > 	if (dirty > limit)
> > 		return 0;
> > 
> > 	if (dirty < 2*setpoint - limit)
> > 		return 2 * SCALE;
> > 
> > 	x = SCALE * (setpoint - dirty) / (limit - setpoint);
> > 	xx = (x * x) / SCALE;
> > 	xxx = (xx * x) / SCALE;
> > 
> > 	return xxx;
> > }
> 
> Looks very neat, much simpler than the three curves solution!
> 
> Thanks,
> Fengguang

Download attachment "3rd-order-limit=thresh+halfscope.png" of type "image/png" (30247 bytes)

Download attachment "3rd-order-limit=thresh.png" of type "image/png" (28785 bytes)