linux-kernel - Re: [PATCH] mm, swap: Make VMA based swap readahead configurable

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Message-Id: <20171002144903.d58ed6887adfd9dc4cdfd697@linux-foundation.org>
Date:   Mon, 2 Oct 2017 14:49:03 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     "Huang, Ying" <ying.huang@...el.com>,
        Michal Hocko <mhocko@...nel.org>,
        Minchan Kim <minchan@...nel.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Johannes Weiner <hannes@...xchg.org>,
        Rik van Riel <riel@...hat.com>, Shaohua Li <shli@...nel.org>,
        Hugh Dickins <hughd@...gle.com>,
        Fengguang Wu <fengguang.wu@...el.com>,
        Tim Chen <tim.c.chen@...el.com>
Subject: Re: [PATCH] mm, swap: Make VMA based swap readahead configurable

On Mon, 2 Oct 2017 08:45:40 -0700 Dave Hansen <dave.hansen@...el.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.