linux-kernel - Re: [GIT PULL] MM updates for 5.20-rc1

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Message-Id: <20220805170752.d609551360017d60903e5e75@linux-foundation.org>
Date:   Fri, 5 Aug 2022 17:07:52 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Roman Gushchin <roman.gushchin@...ux.dev>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Kent Overstreet <kent.overstreet@...il.com>,
        mm-commits@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Dave Chinner <dchinner@...hat.com>,
        Joe Perches <joe@...ches.com>
Subject: Re: [GIT PULL] MM updates for 5.20-rc1

On Fri, 5 Aug 2022 17:04:28 -0700 Roman Gushchin <roman.gushchin@...ux.dev> wrote:

> On Fri, Aug 05, 2022 at 04:32:34PM -0700, Linus Torvalds wrote:
> > On Wed, Aug 3, 2022 at 1:35 PM Andrew Morton <akpm@...ux-foundation.org> wrote:
> > >
> > > - memcg debug/visibility work from Roman Gushchin
> > 
> > Well, not just memcg.
> > 
> > There's that new CONFIG_SHRINKER_DEBUG too.
> > 
> > Which looks like yet another "people add Kconfig options incorrectly".
> > 
> > We don't make new features "default y" unless there's some truly
> > pressing reason for it (ie "99.9% of all people will want this" or "we
> > used to always compile this in, now it's optional").
> 
> Hi Linus!
> 
> It actually was 'default n' in one of the earlier version of the patchset
> and has been switched to 'default y' based on the following feedback from
> Dave Chinner (https://lore.kernel.org/lkml/YmiWK56bOHyrr64u@rh/):
> 
>     No. The argument that "if we turn it off there's no overhead" means
>     one of two things:
> 
>     1. nobody turns it on and it never gets tested and so bitrots and is
>     useless, or
>     2. distro's all turn it on because some tool they ship or customer
>     they ship to wants it.
> 
>     Either way, hiding it behind a config option is not an acceptible
>     solution for mering poorly thought out infrastructure.
> 
> Personally I think that the feature is not that useful for the majority
> of users (this is why default was n), but it's not adding much of the
> overhead, so I had no strong reasons to oppose Dave.
> Cc'ing him just in case.
> 

We should have changelogged these considerations.

I've asked Joe if checkpatch can get a "default y" detector, to draw
attention to this in the future.