Re: [PATCH v3 02/14] arm64: drop ranges in definition of ARCH_FORCE_MAX_ORDER

[Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>]

On Wed, 12 Apr 2023 18:27:08 +0100 Catalin Marinas <catalin.marinas@xxxxxxx> wrote:

> > It sounds nice in theory. In practice. EXPERT hides too much. When you
> > flip expert, you expose over a 175ish new config options which are
> > hidden behind EXPERT.  You don't have to know what you are doing just
> > with the MAX_ORDER, but a whole bunch more as well.  If everyone were
> > already running 10, this might be less of a problem. At least Fedora
> > and RHEL are running 13 for 4K pages on aarch64. This was not some
> > accidental choice, we had to carry a patch to even allow it for a
> > while.  If this does go in as is, we will likely just carry a patch to
> > remove the "if EXPERT", but that is a bit of a disservice to users who
> > might be trying to debug something else upstream, bisecting upstream
> > kernels or testing a patch.  In those cases, people tend to use
> > pristine upstream sources without distro patches to verify, and they
> > tend to use their existing configs. With this change, their MAX_ORDER
> > will drop to 10 from 13 silently.   That can look like a different
> > issue enough to ruin a bisect or have them give bad feedback on a
> > patch because it introduces a "regression" which is not a regression
> > at all, but a config change they couldn't see.
> 
> If we remove EXPERT (as prior to this patch), I'd rather keep the ranges
> and avoid having to explain to people why some random MAX_ORDER doesn't
> build (keeping the range would also make sense for randconfig, not sure
> we got to any conclusion there).

Well this doesn't seem to have got anywhere.  I think I'll send the
patchset into Linus for the next merge window as-is.  Please let's take
a look at this Kconfig presentation issue during the following -rc
cycle.