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Date: Mon, 2 Oct 2017 14:49:03 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Dave Hansen <dave.hansen@intel.com>
Cc: "Huang, Ying" <ying.huang@intel.com>, Michal Hocko <mhocko@kernel.org>,
        Minchan Kim <minchan@kernel.org>, linux-mm@kvack.org,
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        Hugh Dickins <hughd@google.com>, Fengguang Wu <fengguang.wu@intel.com>,
        Tim Chen <tim.c.chen@intel.com>
Subject: Re: [PATCH] mm, swap: Make VMA based swap readahead configurable
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On Mon, 2 Oct 2017 08:45:40 -0700 Dave Hansen <dave.hansen@intel.com> wrote:

> On 09/27/2017 06:02 PM, Huang, Ying wrote:
> > I still think there may be a performance regression for some users
> > because of the change of the algorithm and the knobs, and the
> > performance regression can be resolved via setting the new knob.  But I
> > don't think there will be a functionality regression.  Do you agree?
> 
> A performance regression is a regression.  I don't understand why we are
> splitting hairs as to what kind of regression it is.
> 

Yes.

Ying, please find us a way of avoiding any disruption to existing
system setups.  One which doesn't require that the operator perform a
configuration change to restore prior behaviour/performance.  And
please let's get this done well in advance of the 4.14 release.

Thanks.