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

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Message-ID: <20170927141008.GA1278@bgram>
Date:   Wed, 27 Sep 2017 23:10:08 +0900
From:   Minchan Kim <minchan@...nel.org>
To:     Michal Hocko <mhocko@...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, Sep 27, 2017 at 03:50:34PM +0200, Michal Hocko wrote:
> 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.

Indeed but Huang doesn't think so. He has thought it's not a regression.
Frankly speaking, I'm really bored of discussing with it.
https://marc.info/?l=linux-mm&m=150526413319763&w=2

So I passed the decision to Andrew.
http://lkml.kernel.org/r/<20170913014019.GB29422@...x>

The config option idea is compromise approach although I don't like it
and still believe it's simple clear *regression* so 0 page-cluster
should keep the swap readahead disabled.

> 
> 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.

I absolutely agree but as I said, the discussion was not productive
even though I did best effort to persuade. That's all for my side as
contributor/reviewer. Decision is up to maintainer. ;-)

Thanks for the opinion, Michal.