Re: [PATCH v5 18/25] mm/s390: Use general page fault accounting

Alexander Gordeev
2020-07-08T05:50:04Z

On Tue, Jul 07, 2020 at 06:50:14PM -0400, Peter Xu wrote:
> Use the general page fault accounting by passing regs into handle_mm_fault().
> It naturally solve the issue of multiple page fault accounting when page fault
> retry happened.
>
> CC: Heiko Carstens <heiko.carstens@de.ibm.com>
> CC: Vasily Gorbik <gor@linux.ibm.com>
> CC: Christian Borntraeger <borntraeger@de.ibm.com>
> CC: linux-s390@vger.kernel.org
> Reviewed-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
> Acked-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
> Signed-off-by: Peter Xu <peterx@redhat.com>
> ---
> arch/s390/mm/fault.c | 16 +---------------
> 1 file changed, 1 insertion(+), 15 deletions(-)
>
> diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c
> index fc14df0b4d6e..9aa201df2e94 100644
> --- a/arch/s390/mm/fault.c
> +++ b/arch/s390/mm/fault.c
> @@ -478,7 +478,7 @@ static inline vm_fault_t do_exception(struct pt_regs *regs, int access)
> * make sure we exit gracefully rather than endlessly redo
> * the fault.
> */
> - fault = handle_mm_fault(vma, address, flags, NULL);
> + fault = handle_mm_fault(vma, address, flags, regs);
> if (fault_signal_pending(fault, regs)) {
> fault = VM_FAULT_SIGNAL;
> if (flags & FAULT_FLAG_RETRY_NOWAIT)
> @@ -488,21 +488,7 @@ static inline vm_fault_t do_exception(struct pt_regs *regs, int access)
> if (unlikely(fault & VM_FAULT_ERROR))
> goto out_up;
>
> - /*
> - * Major/minor page fault accounting is only done on the
> - * initial attempt. If we go through a retry, it is extremely
> - * likely that the page will be found in page cache at that point.
> - */
> if (flags & FAULT_FLAG_ALLOW_RETRY) {

Shouldn't this check ^^^ be dropped as well?

Since commit 4064b9827063 ("mm: allow VM_FAULT_RETRY for multiple times")
FAULT_FLAG_ALLOW_RETRY never gets unset, so no need to check..

> - if (fault & VM_FAULT_MAJOR) {
> - tsk->maj_flt++;
> - perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, 1,
> - regs, address);
> - } else {
> - tsk->min_flt++;
> - perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1,
> - regs, address);
> - }
> if (fault & VM_FAULT_RETRY) {
> if (IS_ENABLED(CONFIG_PGSTE) && gmap &&
> (flags & FAULT_FLAG_RETRY_NOWAIT)) {
> --
> 2.26.2
>