[PATCH 18/26] mm/s390: Use general page fault accounting

[PATCH 18/26] mm/s390: Use general page fault accounting

[Peter Xu]

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
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 ab6d7eedcfab..4d62ca7d3e09 100644
--- a/arch/s390/mm/fault.c
+++ b/arch/s390/mm/fault.c
@@ -479,7 +479,7 @@ 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)
@@ -489,21 +489,7 @@ 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) {
-		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

Re: [PATCH 18/26] mm/s390: Use general page fault accounting

[Gerald Schaefer]

On Fri, 19 Jun 2020 12:13:35 -0400
Peter Xu <peterx@redhat.com> 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
> 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 ab6d7eedcfab..4d62ca7d3e09 100644
> --- a/arch/s390/mm/fault.c
> +++ b/arch/s390/mm/fault.c
> @@ -479,7 +479,7 @@ 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)
> @@ -489,21 +489,7 @@ static inline vm_fault_t do_exception(struct pt_regs *regs, int access)
>  	if (unlikely(fault & VM_FAULT_ERROR))
>  		goto out_up;

There are two cases here where we skipped the accounting,
fault_signal_pending() and VM_FAULT_ERROR, similar to other archs.

fault_signal_pending() should be ok, because that only seems to be true
for fault & VM_FAULT_RETRY, in which case the new approach also skips
the accounting.

But for VM_FAULT_ERROR, the new approach would do accounting, IIUC. Is
that changed on purpose? See also my reply on [PATCH 01/26].

Regards,
Gerald

Re: [PATCH 18/26] mm/s390: Use general page fault accounting

[Peter Xu]

On Wed, Jun 24, 2020 at 08:49:30PM +0200, Gerald Schaefer wrote:
> On Fri, 19 Jun 2020 12:13:35 -0400
> Peter Xu <peterx@redhat.com> 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
> > 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 ab6d7eedcfab..4d62ca7d3e09 100644
> > --- a/arch/s390/mm/fault.c
> > +++ b/arch/s390/mm/fault.c
> > @@ -479,7 +479,7 @@ 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)
> > @@ -489,21 +489,7 @@ static inline vm_fault_t do_exception(struct pt_regs *regs, int access)
> >  	if (unlikely(fault & VM_FAULT_ERROR))
> >  		goto out_up;
> 
> There are two cases here where we skipped the accounting,
> fault_signal_pending() and VM_FAULT_ERROR, similar to other archs.
> 
> fault_signal_pending() should be ok, because that only seems to be true
> for fault & VM_FAULT_RETRY, in which case the new approach also skips
> the accounting.

IMHO it's still possible to have fault_signal_pending() return true even if the
fault is not with VM_FAULT_RETRY, e.g., when the signal is delivered right
after the fault is correctly handled for the thread.  However I hope we can
avoid considering that too even if so...

> 
> But for VM_FAULT_ERROR, the new approach would do accounting, IIUC. Is
> that changed on purpose? See also my reply on [PATCH 01/26].

(replied in the other thread)

Thanks,

-- 
Peter Xu

[PATCH 18/26] mm/s390: Use general page fault accounting

[Peter Xu]

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
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 ab6d7eedcfab..4d62ca7d3e09 100644
--- a/arch/s390/mm/fault.c
+++ b/arch/s390/mm/fault.c
@@ -479,7 +479,7 @@ 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)
@@ -489,21 +489,7 @@ 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) {
-		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