Re: [PATCH] erofs: fix EROFS_FS_ZIP_LZMA_DEFAULT_MAX_STREAMS on some UP platforms

[Gao Xiang <xiang@kernel.org>]

On Mon, Aug 17, 2026 at 10:05:09AM +0200, Geert Uytterhoeven wrote:
> Hi Gao,
> 
> On Mon, 17 Aug 2026 at 09:49, Gao Xiang <xiang@kernel.org> wrote:
> > On Mon, Aug 17, 2026 at 09:32:51AM +0200, Geert Uytterhoeven wrote:
> > > Thanks for your patch, which is now commit a64d500b0078e16e ("erofs: fix
> > > EROFS_FS_ZIP_LZMA_DEFAULT_MAX_STREAMS on some UP platforms") in v7.2.
> > >
> > > > --- a/fs/erofs/Kconfig
> > > > +++ b/fs/erofs/Kconfig
> > > > @@ -134,7 +134,8 @@ config EROFS_FS_ZIP_LZMA
> > > >  config EROFS_FS_ZIP_LZMA_DEFAULT_MAX_STREAMS
> > > >         int "EROFS LZMA default maximum decompression streams"
> > > >         depends on EROFS_FS_ZIP_LZMA
> > > > -       range 1 NR_CPUS
> > > > +       range 1 NR_CPUS if SMP
> > > > +       range 1 1 if !SMP
> > > >         default 16
> > >
> > > I have just discovered another oddity: when you have less than 16
> > > CPUS (including SMP=n), this default value is invalid, and "make
> > > savedefconfig" will always write a line like
> > >
> > >     CONFIG_EROFS_FS_ZIP_LZMA_DEFAULT_MAX_STREAMS=1
> > >
> > > to the defconfig file, even if that is the default suggested value.
> > >
> > > Needlessly polluting the defconfig files could be fixed using:
> > >
> > >     -       default 16
> > >     +       default 16 if SMP && NR_CPUS >= 16
> > >     +       default NR_CPUS if SMP
> >
> > I guess `default NR_CPUS if SMP && NR_CPUS < 16` would be better,
> > I'm not sure since I'm not handy in Kconfig stuffs.
> 
> Kconfig always picks the first matching default value, so you don't
> have to exclude the "SMP && NR_CPUS >= 16" case here.
> 
> > >     +       default 1 if !SMP
> 
> If all architectures would always define NR_CPUS, one could replace
> the last two lines by
> 
>     default NR_CPUS
> 
> > >
> > > Thoughts?
> >
> > In principle, that would be better, but may I ask if there is some
> > severe consequences out of one extra line of
> > CONFIG_EROFS_FS_ZIP_LZMA_DEFAULT_MAX_STREAMS=1?
> >
> > Since it has been fixed for many times, I hope if it could be improved
> > later if no severe impacts, sigh..
> 
> It causes more churn (defconfig updates), and makes the defconfig
> files larger than needed.

Could you submit a formal patch directly (since you found it and
suggested a version)?

so I could submit it along with the pull request if you're fine with it.

Thanks,
Gao Xiang

> 
> Gr{oetje,eeting}s,
> 
>                         Geert
> 
> -- 
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
> 
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
>                                 -- Linus Torvalds
>