linux-kernel - RE: [PATCHv6 4/8] zswap: add to mm/

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Date:	Thu, 28 Feb 2013 11:50:58 -0800 (PST)
From:	Dan Magenheimer <dan.magenheimer@...cle.com>
To:	Dan Magenheimer <dan.magenheimer@...cle.com>,
	Seth Jennings <sjenning@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Nitin Gupta <ngupta@...are.org>,
	Minchan Kim <minchan@...nel.org>,
	Konrad Wilk <konrad.wilk@...cle.com>,
	Robert Jennings <rcj@...ux.vnet.ibm.com>,
	Jenifer Hopper <jhopper@...ibm.com>,
	Mel Gorman <mgorman@...e.de>,
	Johannes Weiner <jweiner@...hat.com>,
	Rik van Riel <riel@...hat.com>,
	Larry Woodman <lwoodman@...hat.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	Joe Perches <joe@...ches.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Cody P Schafer <cody@...ux.vnet.ibm.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, devel@...verdev.osuosl.org
Subject: RE: [PATCHv6 4/8] zswap: add to mm/

> From: Dan Magenheimer
> Sent: Thursday, February 28, 2013 11:13 AM
> To: Seth Jennings; Andrew Morton
> Cc: Greg Kroah-Hartman; Nitin Gupta; Minchan Kim; Konrad Rzeszutek Wilk; Dan Magenheimer; Robert
> Jennings; Jenifer Hopper; Mel Gorman; Johannes Weiner; Rik van Riel; Larry Woodman; Benjamin
> Herrenschmidt; Dave Hansen; Joe Perches; Joonsoo Kim; Cody P Schafer; linux-mm@...ck.org; linux-
> kernel@...r.kernel.org; devel@...verdev.osuosl.org
> Subject: RE: [PATCHv6 4/8] zswap: add to mm/
> 
> > From: Seth Jennings [mailto:sjenning@...ux.vnet.ibm.com]
> > Subject: [PATCHv6 4/8] zswap: add to mm/
> >
> > +/*
> > + * Maximum compression ratio, as as percentage, for an acceptable
> > + * compressed page. Any pages that do not compress by at least
> > + * this ratio will be rejected.
> > +*/
> > +static unsigned int zswap_max_compression_ratio = 80;
> > +module_param_named(max_compression_ratio,
> > +			zswap_max_compression_ratio, uint, 0644);
> 
> Unless this is a complete coincidence, I believe that
> the default value "80" is actually:
> 
> (100 * (1L >> ZS_MAX_ZSPAGE_ORDER)) /
>         ((1L >> ZS_MAX_ZSPAGE_ORDER)) + 1)

Doh! If it wasn't obvious, those should be left
shift operators, not right shift.  So....

(100 * (1L << ZS_MAX_ZSPAGE_ORDER)) /
        ((1L << ZS_MAX_ZSPAGE_ORDER)) + 1)

Sorry for that.
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