Re: [PATCH v4] mm: Avoid unnecessary page fault retires on shared memory types
Am 30.05.22 um 18:00 schrieb Peter Xu:
On Mon, May 30, 2022 at 11:52:54AM -0400, Peter Xu wrote:
On Mon, May 30, 2022 at 11:35:10AM +0200, Christian Borntraeger wrote:
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;
Hmm, right after I replied I found "goto out" could be problematic, since
all s390 callers of do_exception() will assume it an error condition (side
note: "goto out_gmap" contains one step to clear "fault" to 0). I'll
replace this with "return 0" instead if it looks good to both of you.
I'll wait for a confirmation before reposting. Thanks,
Yes, that sounds good and thank you for double checking.
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Re: [PATCH v4] mm: Avoid unnecessary page fault retires on shared memory types
On Mon, May 30, 2022 at 07:03:31PM +0200, Heiko Carstens wrote:
> On Mon, May 30, 2022 at 12:00:52PM -0400, Peter Xu wrote:
> > On Mon, May 30, 2022 at 11:52:54AM -0400, Peter Xu wrote:
> > > On Mon, May 30, 2022 at 11:35:10AM +0200, Christian Borntraeger wrote:
> > > > > 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;
> > > > > + }
> fault = 0; <
> > > > > + goto out;
> >
> > Hmm, right after I replied I found "goto out" could be problematic, since
> > all s390 callers of do_exception() will assume it an error condition (side
> > note: "goto out_gmap" contains one step to clear "fault" to 0). I'll
> > replace this with "return 0" instead if it looks good to both of you.
> >
> > I'll wait for a confirmation before reposting. Thanks,
>
> Right, that was stupid. Thanks for double checking!
>
> However could you please add "fault = 0" just in front of the goto out
> like above? I'd like to avoid having returns and gotos mixed.
Sure thing.
--
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Re: [PATCH v4] mm: Avoid unnecessary page fault retires on shared memory types
On Mon, May 30, 2022 at 12:00:52PM -0400, Peter Xu wrote:
> On Mon, May 30, 2022 at 11:52:54AM -0400, Peter Xu wrote:
> > On Mon, May 30, 2022 at 11:35:10AM +0200, Christian Borntraeger wrote:
> > > > 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;
> > > > + }
fault = 0; <
> > > > + goto out;
>
> Hmm, right after I replied I found "goto out" could be problematic, since
> all s390 callers of do_exception() will assume it an error condition (side
> note: "goto out_gmap" contains one step to clear "fault" to 0). I'll
> replace this with "return 0" instead if it looks good to both of you.
>
> I'll wait for a confirmation before reposting. Thanks,
Right, that was stupid. Thanks for double checking!
However could you please add "fault = 0" just in front of the goto out
like above? I'd like to avoid having returns and gotos mixed.
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Re: [PATCH v4] mm: Avoid unnecessary page fault retires on shared memory types
On Mon, May 30, 2022 at 11:52:54AM -0400, Peter Xu wrote:
> On Mon, May 30, 2022 at 11:35:10AM +0200, Christian Borntraeger wrote:
> >
> >
> > 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;
Hmm, right after I replied I found "goto out" could be problematic, since
all s390 callers of do_exception() will assume it an error condition (side
note: "goto out_gmap" contains one step to clear "fault" to 0). I'll
replace this with "return 0" instead if it looks good to both of you.
I'll wait for a confirmation before reposting. Thanks,
--
Peter Xu
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Re: [PATCH v4] mm: Avoid unnecessary page fault retires on shared memory types
On Mon, May 30, 2022 at 11:35:10AM +0200, Christian Borntraeger wrote:
>
>
> 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
Looks sane, thanks Heiko, Christian. I'll cook another one.
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Re: [PATCH v4] mm: Avoid unnecessary page fault retires on shared memory types
On Fri, May 27, 2022 at 03:39:36PM -0400, Peter Xu wrote:
> diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
> index 77341b160aca..e401d416bbd6 100644
> --- a/arch/arm64/mm/fault.c
> +++ b/arch/arm64/mm/fault.c
> @@ -607,6 +607,10 @@ static int __kprobes do_page_fault(unsigned long far,
> unsigned int esr,
> return 0;
> }
>
> + /* The fault is fully completed (including releasing mmap lock) */
> + if (fault & VM_FAULT_COMPLETED)
> + return 0;
> +
> if (fault & VM_FAULT_RETRY) {
> mm_flags |= FAULT_FLAG_TRIED;
> goto retry;
For arm64:
Acked-by: Catalin Marinas
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Re: [PATCH v4] mm: Avoid unnecessary page fault retires on shared memory types
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
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Re: [PATCH v4] mm: Avoid unnecessary page fault retires on shared memory types
On Fri, May 27, 2022 at 03:39:36PM -0400, Peter Xu wrote:
> diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c
> index e173b6187ad5..4608cc962ecf 100644
> --- a/arch/s390/mm/fault.c
> +++ b/arch/s390/mm/fault.c
> @@ -433,6 +433,17 @@ static inline vm_fault_t do_exception(struct pt_regs
> *regs, int access)
> goto out_up;
> goto out;
> }
> +
> + /* 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 (unlikely(fault & VM_FAULT_ERROR))
> goto out_up;
>
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;
}
if (unlikely(fault & VM_FAULT_ERROR))
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