Re: [PATCH v2 5/6] s390/mm: Batch PTE updates in lazy MMU mode

[Heiko Carstens <hca@linux.ibm.com>]

On Wed, Apr 15, 2026 at 05:01:23PM +0200, Alexander Gordeev wrote:
> diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
> index 7828fbe0fc42..deffc819268e 100644
> --- a/arch/s390/Kconfig
> +++ b/arch/s390/Kconfig
> @@ -732,6 +732,17 @@ config MAX_PHYSMEM_BITS
>  	  Increasing the number of bits also increases the kernel image size.
>  	  By default 46 bits (64TB) are supported.
>  
> +config IPTE_BATCH
> +	def_bool y
> +	prompt "Enables Additional Entries for IPTE instruction"
> +	select ARCH_HAS_LAZY_MMU_MODE
> +	help
> +	  This option enables using of "Additional Entries" field of the IPTE
> +	  instruction, which capitalizes on the lazy MMU mode infrastructure.
> +	  As result, multiple PTEs are invalidated in one go. That improves
> +	  performance of many memory-management system calls (like mremap(),
> +	  mprotect(), etc.) and decreases CEC-wide quiesce traffic.
> +
>  endmenu

Just some general comments before I find time to look deeper into this
series: please let us not add yet another config option. This will be
enabled anywhere in any case.

Not having this option makes maintenance easier.

> +#if !defined(CONFIG_IPTE_BATCH) || defined(__DECOMPRESSOR)
> +static inline
> +bool ipte_batch_ptep_test_and_clear_young(struct vm_area_struct *vma,
> +					  unsigned long addr, pte_t *ptep,
> +					  int *res)
> +{
> +	return false;
> +}

Why does this depend on __DECOMPRESSOR? Which code in the decompressor
would generate a call to the ipte_batch functions?