Re: [PATCH v7 2/4] s390/mm: Batch PTE updates in lazy MMU mode

[sashiko-bot@kernel.org]

> Make use of the IPTE instruction's "Additional Entries" field to
> invalidate multiple PTEs in one go while in lazy MMU mode. This
> is the mode in which many memory-management system calls (like
> mremap(), mprotect(), etc.) update memory attributes.
> 
> To achieve that, the set_pte() and ptep_get() primitives use a
> per-CPU cache to store and retrieve PTE values and apply the
> cached values to the real page table once lazy MMU mode is left.
> 
> The same is done for memory-management platform callbacks that
> would otherwise cause intense per-PTE IPTE traffic, reducing the
> number of IPTE instructions from up to PTRS_PER_PTE to a single
> instruction in the best case. The average reduction is of course
> smaller.
> 
> [ ... ]
> In an extreme case of mprotect() contiguously triggering the
> quiesce state on four LPARs in parallel, measurements show
> ~25x fewer quiesce events.
> 
> Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>

Sashiko has reviewed this patch and found no issues. It looks great!

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