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

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Message-ID: <20170927135034.yatxlhvunawzmcar@dhcp22.suse.cz>
Date:   Wed, 27 Sep 2017 15:50:34 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Minchan Kim <minchan@...nel.org>
Cc:     "Huang, Ying" <ying.huang@...el.com>,
        Andrew Morton <akpm@...ux-foundation.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>,
        Dave Hansen <dave.hansen@...el.com>
Subject: Re: [PATCH] mm, swap: Make VMA based swap readahead configurable

On Wed 27-09-17 22:41:17, Minchan Kim wrote:
> On Wed, Sep 27, 2017 at 03:22:41PM +0200, Michal Hocko wrote:
[...]
> > simply cannot disable swap readahead when page-cluster is 0?
> 
> That's was what I want really but Huang want to use two readahead
> algorithms in parallel so he wanted to keep two separated disable
> knobs.

If it breaks existing and documented behavior then it is a clear
regression and it should be fixed. I do not see why this should be
disputable at all.

Working around an issue with a config option sounds like the wrong way
to go because those who cannot do that unconditionally would still see a
regression.
-- 
Michal Hocko
SUSE Labs