linux-kernel - Re: retiring laptop_mode? was Re: [PATCH] mm: vmscan: always allow writeback during memcg reclaim

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Message-ID: <aUOYd6FiIBf06Skt@infradead.org>
Date: Wed, 17 Dec 2025 22:00:23 -0800
From: Christoph Hellwig <hch@...radead.org>
To: Johannes Weiner <hannes@...xchg.org>
Cc: Christoph Hellwig <hch@...radead.org>, Jens Axboe <axboe@...nel.dk>,
	Deepanshu Kartikey <kartikey406@...il.com>,
	akpm@...ux-foundation.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, linux-block@...r.kernel.org
Subject: Re: retiring laptop_mode? was Re: [PATCH] mm: vmscan: always allow
 writeback during memcg reclaim

On Tue, Dec 16, 2025 at 01:52:01PM -0500, Johannes Weiner wrote:
> On Mon, Dec 15, 2025 at 11:41:07PM -0800, Christoph Hellwig wrote:
> > On Mon, Dec 15, 2025 at 03:08:38PM -0500, Johannes Weiner wrote:
> > > Debated whether to add some sort of deprecation sysctl handler, but at
> > > least systemd-sysctl just prints a warning and still applies other
> > > settings from the same config file.
> > 
> > In general dropping sysctl will break things.  So I think we'll need
> > a stub, at which point it might as well warn for a while.
> 
> Fair enough, I added that.
> 
> Jens, that change seemed small enough that I carried your Ack, but
> please let me know if you feel otherwise ;)
> 
> > > Laptop mode was introduced to save battery, by delaying and
> > > consolidating writes and maximize the time rotating hard drives
> > > wouldn't have to spin. Needless to say, this is a scenario of the
> > > (in)glorious past.
> > 
> > Maybe expand on this a bit by mentioning that reclaim now never does
> > file system writeback, and fs writeback is already very lumpy by
> > design.  And of cours that hard disk with their high spinup latency
> > and extra power draw are a thing of the past in laptops or other mobile
> > devices.
> 
> Sounds good. Can you take a look at the new version below?

Looks good:

Reviewed-by: Christoph Hellwig <hch@....de>