Re: [PATCH v3] erofs: cap LZMA stream pool size

On 8/12/26 03:54, Gao Xiang wrote:
> Hi Geert,
> 
> On Wed, Aug 12, 2026 at 11:30:14AM +0200, Geert Uytterhoeven wrote:
>> Hi Gao,
>>
>> On Wed, 12 Aug 2026 at 01:37, Gao Xiang <[email protected]> wrote:
>>> On Tue, Aug 11, 2026 at 03:37:38PM -0400, Michael Bommarito wrote:
>>>> On Tue, Aug 11, 2026 at 3:35 PM Guenter Roeck <[email protected]> wrote:
>>>>>> Any progress with fixing this for v7.2?
>>>>
>>>> I would like to fix this since I started the problem with the original
>>>> patch, but I feel a bit stuck.  My v1 and v2 patches would not have
>>>> triggered the build failure, but Gao made valid points about the
>>>> trade-offs that led us to this v3.  Maybe it would be worth your
>>>> opinion on the config approach in those earlier patches?
>>>
>>> Sorry about the late reply.
>>>
>>> As I said, I really dislike hardcoded range, but it is an issue that no
>>> NR_CPUS definition on CONFIG_SMP:
>>>
>>> I wonder if the following diff resolves the m68k issue (I'm not an
>>> Kconfig expert but it seems to work on x86_64 !CONFIG_SMP):
>>>
>>> diff --git a/fs/erofs/Kconfig b/fs/erofs/Kconfig
>>> index 8ca1767dafb6..2dfc313588d2 100644
>>> --- 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
>>>          help
>>>            By default EROFS allocates one LZMA decompression stream per CPU.
>>
>> Thank you, that seems to work (despite still seeing the warning on m68k,
>> as NR_CPUS does not exist).
>>
> 
> ...
> 
>>
>>        $ make ARCH=m68k allmodconfig
>>       fs/erofs/Kconfig:137:warning: range is invalid
>>
>>   Warning...
>>
> 
> Yes, other arches shouldn't have the warning because I think other
> arches (including microblaze) defines NR_CPUS in Kconfig, except m68k.
> 

That is not entirely true. openrisc only has it if SMP=y. But it still
does not generate the warning for some reason.

> The following diff can eliminate the m68k warning above, I think m68k
> folks could consider this way if you really don't want to define an
> explicit NR_CPUS.  Anyway, I think it should go with another patch:
> 
> ```
> diff --git a/arch/m68k/Kconfig b/arch/m68k/Kconfig
> index 11835eb59d94..90499f126c73 100644
> --- a/arch/m68k/Kconfig
> +++ b/arch/m68k/Kconfig
> @@ -44,6 +44,9 @@ config M68K
>   	select UACCESS_MEMCPY if !MMU
>   	select ZONE_DMA
>   
> +config NR_CPUS
> +	int

I would suggest to add

	default 1

Guenter

> +
>   config CPU_BIG_ENDIAN
>   	def_bool y
> ```
> 
> I will try to form a formal patch (with the diff in the previous reply)
> directly to Linus (since I don't have other urgent patches for
> Linux 7.2.)
> 
> Thanks,
> Gao Xiang