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Date: Thu, 28 Feb 2013 11:50:58 -0800 (PST)
From: Dan Magenheimer <dan.magenheimer@oracle.com>
Subject: RE: [PATCHv6 4/8] zswap: add to mm/
References: <<1361397888-14863-1-git-send-email-sjenning@linux.vnet.ibm.com>>
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To: Dan Magenheimer <dan.magenheimer@oracle.com>, Seth Jennings <sjenning@linux.vnet.ibm.com>, Andrew Morton <akpm@linux-foundation.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Nitin Gupta <ngupta@vflare.org>, Minchan Kim <minchan@kernel.org>, Konrad Wilk <konrad.wilk@oracle.com>, Robert Jennings <rcj@linux.vnet.ibm.com>, Jenifer Hopper <jhopper@us.ibm.com>, Mel Gorman <mgorman@suse.de>, Johannes Weiner <jweiner@redhat.com>, Rik van Riel <riel@redhat.com>, Larry Woodman <lwoodman@redhat.com>, Benjamin Herrenschmidt <benh@kernel.crashing.org>, Dave Hansen <dave@linux.vnet.ibm.com>, Joe Perches <joe@perches.com>, Joonsoo Kim <iamjoonsoo.kim@lge.com>, Cody P Schafer <cody@linux.vnet.ibm.com>, linux-mm@kvack.org, linux-kernel@vger.kernel.org, devel@driverdev.osuosl.org

> 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; Larr=
y Woodman; Benjamin
> Herrenschmidt; Dave Hansen; Joe Perches; Joonsoo Kim; Cody P Schafer; lin=
ux-mm@kvack.org; linux-
> kernel@vger.kernel.org; devel@driverdev.osuosl.org
> Subject: RE: [PATCHv6 4/8] zswap: add to mm/
>=20
> > From: Seth Jennings [mailto:sjenning@linux.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 =3D 80;
> > +module_param_named(max_compression_ratio,
> > +=09=09=09zswap_max_compression_ratio, uint, 0644);
>=20
> Unless this is a complete coincidence, I believe that
> the default value "80" is actually:
>=20
> (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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