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

Christoph Hellwig
2025-12-16T07:41:13Z

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.

> 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.

Otherwise this looks good to me.