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

[Geert Uytterhoeven]

Hi Gao,

On Mon, 17 Aug 2026 at 09:49, Gao Xiang <xiang@xxxxxxxxxx> 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.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

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