Re: [PATCH] erofs: Fix EROFS_FS_ZIP_LZMA_DEFAULT_MAX_STREAMS default logic

[Guenter Roeck <linux@roeck-us.net>]

On Thu, Aug 20, 2026 at 12:00:23PM +0200, Geert Uytterhoeven wrote:
> When NR_CPUS is less than 16, or when SMP is disabled, the default value
> of 16 is invalid.
> 
> While actual configuration picks up a sensible and valid default
> (NR_CPUS or 1), "make savedefconfig" will still write a line like
> 
>     CONFIG_EROFS_FS_ZIP_LZMA_DEFAULT_MAX_STREAMS=1
> 
> to the defconfig file, even if that matches the sensible default.
> 
> Avoid needlessly enlarging the defconfig files, and reduce churn for
> updating them, by specifying valid defaults depending on SMP and
> NR_CPUS.
> 
> While at it, make the prompt depend on SMP, as there is no point in
> asking the user about the maximum number of decompression streams if
> there is only one valid answer.
> 

Absolutely agree.

> Fixes: c9b47e6b23114e93 ("erofs: cap LZMA stream pool size")
> Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>

Reviewed-by: Guenter Roeck <linux@roeck-us.net>

> ---
>  fs/erofs/Kconfig | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/erofs/Kconfig b/fs/erofs/Kconfig
> index 2dfc313588d283a0..37495e95a78d9bf6 100644
> --- a/fs/erofs/Kconfig
> +++ b/fs/erofs/Kconfig
> @@ -132,11 +132,13 @@ config EROFS_FS_ZIP_LZMA
>  	  Say N if you want to disable LZMA compression support.
>  
>  config EROFS_FS_ZIP_LZMA_DEFAULT_MAX_STREAMS
> -	int "EROFS LZMA default maximum decompression streams"
> +	int "EROFS LZMA default maximum decompression streams" if SMP
>  	depends on EROFS_FS_ZIP_LZMA
>  	range 1 NR_CPUS if SMP
>  	range 1 1 if !SMP
> -	default 16
> +	default 16 if SMP && NR_CPUS >= 16
> +	default NR_CPUS if SMP
> +	default 1
>  	help
>  	  By default EROFS allocates one LZMA decompression stream per CPU.
>  	  Each stream can hold a dictionary of up to 8 MiB taken from the
> @@ -144,7 +146,7 @@ config EROFS_FS_ZIP_LZMA_DEFAULT_MAX_STREAMS
>  	  of memory.  This caps the default; the lzma_streams module parameter
>  	  still overrides it.
>  
> -	  If unsure, keep the default of 16.
> +	  If unsure, keep the suggested default (16 or lower).
>  
>  config EROFS_FS_ZIP_DEFLATE
>  	bool "EROFS DEFLATE compressed data support"
> -- 
> 2.43.0
>