Re: [PATCH v4] mm: Avoid unnecessary page fault retires on shared memory types

Christian Borntraeger
2022-05-30T09:37:11Z

Am 29.05.22 um 22:33 schrieb Heiko Carstens:
[...]
>
> Guess the patch below on top of your patch is what we want.
> Just for clarification: if gmap is not NULL then the process is a kvm
> process. So, depending on the workload, this optimization makes sense.
>
> diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c
> index 4608cc962ecf..e1d40ca341b7 100644
> --- a/arch/s390/mm/fault.c
> +++ b/arch/s390/mm/fault.c
> @@ -436,12 +436,11 @@ static inline vm_fault_t do_exception(struct pt_regs *regs, int access)
>
> /* The fault is fully completed (including releasing mmap lock) */
> if (fault & VM_FAULT_COMPLETED) {
> - /*
> - * Gmap will need the mmap lock again, so retake it. TODO:
> - * only conditionally take the lock when CONFIG_PGSTE set.
> - */
> - mmap_read_lock(mm);
> - goto out_gmap;
> + if (gmap) {
> + mmap_read_lock(mm);
> + goto out_gmap;
> + }
> + goto out;

Yes, that makes sense. With that

Acked-by: Christian Borntraeger <borntraeger@linux.ibm.com>