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

Hi Gao,

On Mon, 17 Aug 2026 at 10:10, Gao Xiang <[email protected]> wrote:
> On Mon, Aug 17, 2026 at 10:05:09AM +0200, Geert Uytterhoeven wrote:
> > On Mon, 17 Aug 2026 at 09:49, Gao Xiang <[email protected]> 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.

Will do, I want to do a bit more testing first...
In addition, usability can be improved by hiding the prompt on UP
systems:

-       int "EROFS LZMA default maximum decompression streams"
+       int "EROFS LZMA default maximum decompression streams" if SMP

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- [email protected]

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