Re: [PATCH v3 00/20] Speculative page faults

Re: [PATCH v3 00/20] Speculative page faults

[Alexei Starovoitov]

On Mon, Sep 18, 2017 at 12:15 AM, Laurent Dufour
<ldufour@linux.vnet.ibm.com> wrote:
> Despite the unprovable lockdep warning raised by Sergey, I didn't get any
> feedback on this series.
>
> Is there a chance to get it moved upstream ?

what is the status ?
We're eagerly looking forward for this set to land,
since we have several use cases for tracing that
will build on top of this set as discussed at Plumbers.

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Re: [PATCH v3 00/20] Speculative page faults

[Andrew Morton]

On Mon, 25 Sep 2017 09:27:43 -0700 Alexei Starovoitov <alexei.starovoitov@gmail.com> wrote:

> On Mon, Sep 18, 2017 at 12:15 AM, Laurent Dufour
> <ldufour@linux.vnet.ibm.com> wrote:
> > Despite the unprovable lockdep warning raised by Sergey, I didn't get any
> > feedback on this series.
> >
> > Is there a chance to get it moved upstream ?
> 
> what is the status ?
> We're eagerly looking forward for this set to land,
> since we have several use cases for tracing that
> will build on top of this set as discussed at Plumbers.

There has been sadly little review and testing so far :(

I'll be taking a close look at it all over the next couple of weeks. 

One terribly important thing (especially for a patchset this large and
intrusive) is the rationale for merging it: the justification, usually
in the form of end-user benefit.

Laurent's [0/n] provides some nice-looking performance benefits for
workloads which are chosen to show performance benefits(!) but, alas,
no quantitative testing results for workloads which we may suspect will
be harmed by the changes(?).  Even things as simple as impact upon
single-threaded pagefault-intensive workloads and its effect upon
CONFIG_SMP=n .text size?

If you have additional usecases then please, spell them out for us in
full detail so we can better understand the benefits which this
patchset provides.

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Re: [PATCH v3 00/20] Speculative page faults

[Laurent Dufour]

Hi Alexei,

Le 25/09/2017 A  18:27, Alexei Starovoitov a A(C)critA :
> On Mon, Sep 18, 2017 at 12:15 AM, Laurent Dufour
> <ldufour@linux.vnet.ibm.com> wrote:
>> Despite the unprovable lockdep warning raised by Sergey, I didn't get any
>> feedback on this series.
>>
>> Is there a chance to get it moved upstream ?
> 
> what is the status ?

As mentioned by Andrew this lacks review and test, what about your 
Ack/Review/Tested-By ?

> We're eagerly looking forward for this set to land,
> since we have several use cases for tracing that
> will build on top of this set as discussed at Plumbers.

Unfortunately I was not able to attend Plumbers this year, but I'll be 
pleased, as well as the MM mailing readers, to get your feedback and use 
cases of this series.

Thanks,
Laurent.

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Re: [PATCH v3 00/20] Speculative page faults

[Laurent Dufour]

Hi,

On 26/09/2017 01:34, Andrew Morton wrote:
> On Mon, 25 Sep 2017 09:27:43 -0700 Alexei Starovoitov <alexei.starovoitov@gmail.com> wrote:
> 
>> On Mon, Sep 18, 2017 at 12:15 AM, Laurent Dufour
>> <ldufour@linux.vnet.ibm.com> wrote:
>>> Despite the unprovable lockdep warning raised by Sergey, I didn't get any
>>> feedback on this series.
>>>
>>> Is there a chance to get it moved upstream ?
>>
>> what is the status ?
>> We're eagerly looking forward for this set to land,
>> since we have several use cases for tracing that
>> will build on top of this set as discussed at Plumbers.
> 
> There has been sadly little review and testing so far :(

I do agree and I could just encourage people to do so :/

> I'll be taking a close look at it all over the next couple of weeks.

Thanks Andrew for giving it a close look.

> One terribly important thing (especially for a patchset this large and
> intrusive) is the rationale for merging it: the justification, usually
> in the form of end-user benefit.

The benefit is only for multi-threaded processes. But even on *small* 
systems with 16 CPUs, there is a real benefit.

> 
> Laurent's [0/n] provides some nice-looking performance benefits for
> workloads which are chosen to show performance benefits(!) but, alas,
> no quantitative testing results for workloads which we may suspect will
> be harmed by the changes(?).

I did test with kernbench, involving gcc/ld which are not 
multi-threaded, AFAIK, and I didn't see any impact.
But if you know additional test I should give a try, please advise.

Regarding ebizzy, it was designed to simulate web server's activity, so 
I guess there will be improvements when running real web servers.

>  Even things as simple as impact upon
> single-threaded pagefault-intensive workloads and its effect upon
> CONFIG_SMP=n .text size?
> 
> If you have additional usecases then please, spell them out for us in
> full detail so we can better understand the benefits which this
> patchset provides.

The other use-case I'm aware of is on memory database, where performance 
improvements is really significant, as I mentioned in the header of my 
series.

Cheers,
Laurent.

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Re: [PATCH v3 00/20] Speculative page faults

[Laurent Dufour]

Hi Andrew,

On 26/09/2017 01:34, Andrew Morton wrote:
> On Mon, 25 Sep 2017 09:27:43 -0700 Alexei Starovoitov <alexei.starovoitov@gmail.com> wrote:
> 
>> On Mon, Sep 18, 2017 at 12:15 AM, Laurent Dufour
>> <ldufour@linux.vnet.ibm.com> wrote:
>>> Despite the unprovable lockdep warning raised by Sergey, I didn't get any
>>> feedback on this series.
>>>
>>> Is there a chance to get it moved upstream ?
>>
>> what is the status ?
>> We're eagerly looking forward for this set to land,
>> since we have several use cases for tracing that
>> will build on top of this set as discussed at Plumbers.
> 
> There has been sadly little review and testing so far :(
> 
> I'll be taking a close look at it all over the next couple of weeks.
> 
> One terribly important thing (especially for a patchset this large and
> intrusive) is the rationale for merging it: the justification, usually
> in the form of end-user benefit.
> 
> Laurent's [0/n] provides some nice-looking performance benefits for
> workloads which are chosen to show performance benefits(!) but, alas,
> no quantitative testing results for workloads which we may suspect will
> be harmed by the changes(?).  Even things as simple as impact upon
> single-threaded pagefault-intensive workloads and its effect upon
> CONFIG_SMP=n .text size?

I forgot to mention in my previous email the impact on the .text section.

Here are the metrics I got :

.text size	UP		SMP		Delta
4.13-mmotm	8444201		8964137		6.16%
'' +spf		8452041		8971929		6.15%
	Delta	0.09%		0.09%	

No major impact as you could see.

Thanks,
Laurent

> If you have additional usecases then please, spell them out for us in
> full detail so we can better understand the benefits which this
> patchset provides.
> 

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Re: [PATCH v3 00/20] Speculative page faults

[Andrew Morton]

On Thu, 28 Sep 2017 14:29:02 +0200 Laurent Dufour <ldufour@linux.vnet.ibm.com> wrote:

> > Laurent's [0/n] provides some nice-looking performance benefits for
> > workloads which are chosen to show performance benefits(!) but, alas,
> > no quantitative testing results for workloads which we may suspect will
> > be harmed by the changes(?).  Even things as simple as impact upon
> > single-threaded pagefault-intensive workloads and its effect upon
> > CONFIG_SMP=n .text size?
> 
> I forgot to mention in my previous email the impact on the .text section.
> 
> Here are the metrics I got :
> 
> .text size	UP		SMP		Delta
> 4.13-mmotm	8444201		8964137		6.16%
> '' +spf		8452041		8971929		6.15%
> 	Delta	0.09%		0.09%	
> 
> No major impact as you could see.

8k text increase seems rather a lot actually.  That's a lot more
userspace cacheclines that get evicted during a fault...

Is the feature actually beneficial on uniprocessor?

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Re: [PATCH v3 00/20] Speculative page faults

[Laurent Dufour]

Hi Andrew,

On 28/09/2017 22:38, Andrew Morton wrote:
> On Thu, 28 Sep 2017 14:29:02 +0200 Laurent Dufour <ldufour@linux.vnet.ibm.com> wrote:
> 
>>> Laurent's [0/n] provides some nice-looking performance benefits for
>>> workloads which are chosen to show performance benefits(!) but, alas,
>>> no quantitative testing results for workloads which we may suspect will
>>> be harmed by the changes(?).  Even things as simple as impact upon
>>> single-threaded pagefault-intensive workloads and its effect upon
>>> CONFIG_SMP=n .text size?
>>
>> I forgot to mention in my previous email the impact on the .text section.
>>
>> Here are the metrics I got :
>>
>> .text size	UP		SMP		Delta
>> 4.13-mmotm	8444201		8964137		6.16%
>> '' +spf		8452041		8971929		6.15%
>> 	Delta	0.09%		0.09%	
>>
>> No major impact as you could see.
> 
> 8k text increase seems rather a lot actually.  That's a lot more
> userspace cacheclines that get evicted during a fault...
> 
> Is the feature actually beneficial on uniprocessor?

This is useless on uniprocessor, and I will disable it on x86 when !SMP 
by not defining __HAVE_ARCH_CALL_SPF.
So the speculative page fault handler will not be built but the vm 
sequence counter and the SCRU stuff will still be there. I may also make 
it disabled through macro when __HAVE_ARCH_CALL_SPF is not defined, but 
this may obfuscated the code a bit...

On ppc64, as this feature requires book3s, it can't be built without SMP 
support.

I rebuild the code on my x86 guest with the following patch applied:
--- a/arch/x86/include/asm/pgtable_types.h
+++ b/arch/x86/include/asm/pgtable_types.h
@@ -260,7 +260,7 @@ enum page_cache_mode {
  /*
   * Advertise that we call the Speculative Page Fault handler.
   */
-#ifdef CONFIG_X86_64
+#if defined(CONFIG_X86_64) && defined(CONFIG_SMP)
  #define __HAVE_ARCH_CALL_SPF
  #endif

And this time I got the following size on UP :
		UP
4.13-mmotm	8444201
'' +spf		8447945 (previously 8452041)
		  +3744

If I disable all the vm_sequence operations and the SRCU stuff this 
would lead to 0.

Thanks,
Laurent.

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Re: [PATCH v3 00/20] Speculative page faults

[Michael Ellerman]

Laurent Dufour <ldufour@linux.vnet.ibm.com> writes:

> Hi Andrew,
>
> On 28/09/2017 22:38, Andrew Morton wrote:
>> On Thu, 28 Sep 2017 14:29:02 +0200 Laurent Dufour <ldufour@linux.vnet.ibm.com> wrote:
>> 
>>>> Laurent's [0/n] provides some nice-looking performance benefits for
>>>> workloads which are chosen to show performance benefits(!) but, alas,
>>>> no quantitative testing results for workloads which we may suspect will
>>>> be harmed by the changes(?).  Even things as simple as impact upon
>>>> single-threaded pagefault-intensive workloads and its effect upon
>>>> CONFIG_SMP=n .text size?
>>>
>>> I forgot to mention in my previous email the impact on the .text section.
>>>
>>> Here are the metrics I got :
>>>
>>> .text size	UP		SMP		Delta
>>> 4.13-mmotm	8444201		8964137		6.16%
>>> '' +spf		8452041		8971929		6.15%
>>> 	Delta	0.09%		0.09%	
>>>
>>> No major impact as you could see.
>> 
>> 8k text increase seems rather a lot actually.  That's a lot more
>> userspace cacheclines that get evicted during a fault...
>> 
>> Is the feature actually beneficial on uniprocessor?
>
> This is useless on uniprocessor, and I will disable it on x86 when !SMP 
> by not defining __HAVE_ARCH_CALL_SPF.
> So the speculative page fault handler will not be built but the vm 
> sequence counter and the SCRU stuff will still be there. I may also make 
> it disabled through macro when __HAVE_ARCH_CALL_SPF is not defined, but 
> this may obfuscated the code a bit...
>
> On ppc64, as this feature requires book3s, it can't be built without SMP 
> support.

Book3S doesn't force SMP, eg. PMAC is Book3S but can be built with SMP=n.

It's true that POWERNV and PSERIES both force SMP, and those are the
platforms used on modern Book3S CPUs.

cheers

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Re: [PATCH v3 00/20] Speculative page faults

[Laurent Dufour]

On 03/10/2017 03:27, Michael Ellerman wrote:
> Laurent Dufour <ldufour@linux.vnet.ibm.com> writes:
> 
>> Hi Andrew,
>>
>> On 28/09/2017 22:38, Andrew Morton wrote:
>>> On Thu, 28 Sep 2017 14:29:02 +0200 Laurent Dufour <ldufour@linux.vnet.ibm.com> wrote:
>>>
>>>>> Laurent's [0/n] provides some nice-looking performance benefits for
>>>>> workloads which are chosen to show performance benefits(!) but, alas,
>>>>> no quantitative testing results for workloads which we may suspect will
>>>>> be harmed by the changes(?).  Even things as simple as impact upon
>>>>> single-threaded pagefault-intensive workloads and its effect upon
>>>>> CONFIG_SMP=n .text size?
>>>>
>>>> I forgot to mention in my previous email the impact on the .text section.
>>>>
>>>> Here are the metrics I got :
>>>>
>>>> .text size	UP		SMP		Delta
>>>> 4.13-mmotm	8444201		8964137		6.16%
>>>> '' +spf		8452041		8971929		6.15%
>>>> 	Delta	0.09%		0.09%	
>>>>
>>>> No major impact as you could see.
>>>
>>> 8k text increase seems rather a lot actually.  That's a lot more
>>> userspace cacheclines that get evicted during a fault...
>>>
>>> Is the feature actually beneficial on uniprocessor?
>>
>> This is useless on uniprocessor, and I will disable it on x86 when !SMP 
>> by not defining __HAVE_ARCH_CALL_SPF.
>> So the speculative page fault handler will not be built but the vm 
>> sequence counter and the SCRU stuff will still be there. I may also make 
>> it disabled through macro when __HAVE_ARCH_CALL_SPF is not defined, but 
>> this may obfuscated the code a bit...
>>
>> On ppc64, as this feature requires book3s, it can't be built without SMP 
>> support.
> 
> Book3S doesn't force SMP, eg. PMAC is Book3S but can be built with SMP=n.
> 
> It's true that POWERNV and PSERIES both force SMP, and those are the
> platforms used on modern Book3S CPUs.

Thanks Michael,

I'll add a check on CONFIG_SMP on ppc too.

Laurent.

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Re: [PATCH v3 00/20] Speculative page faults

[Laurent Dufour]

On 25/09/2017 18:27, Alexei Starovoitov wrote:
> On Mon, Sep 18, 2017 at 12:15 AM, Laurent Dufour
> <ldufour@linux.vnet.ibm.com> wrote:
>> Despite the unprovable lockdep warning raised by Sergey, I didn't get any
>> feedback on this series.
>>
>> Is there a chance to get it moved upstream ?
> 
> what is the status ?
> We're eagerly looking forward for this set to land,
> since we have several use cases for tracing that
> will build on top of this set as discussed at Plumbers.

Hi Alexei,

Based on Plumber's note [1], it sounds that the use case is tied to the BPF
tracing where a call tp find_vma() call will be made on a process's context
to fetch user space's symbols.

Am I right ?
Is the find_vma() call made in the context of the process owning the mm
struct ?

Thanks,
Laurent.

[1] https://etherpad.openstack.org/p/LPC2017_Tracing)

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Re: [PATCH v3 00/20] Speculative page faults

[Alexei Starovoitov]

On Wed, Oct 04, 2017 at 08:50:49AM +0200, Laurent Dufour wrote:
> On 25/09/2017 18:27, Alexei Starovoitov wrote:
> > On Mon, Sep 18, 2017 at 12:15 AM, Laurent Dufour
> > <ldufour@linux.vnet.ibm.com> wrote:
> >> Despite the unprovable lockdep warning raised by Sergey, I didn't get any
> >> feedback on this series.
> >>
> >> Is there a chance to get it moved upstream ?
> > 
> > what is the status ?
> > We're eagerly looking forward for this set to land,
> > since we have several use cases for tracing that
> > will build on top of this set as discussed at Plumbers.
> 
> Hi Alexei,
> 
> Based on Plumber's note [1], it sounds that the use case is tied to the BPF
> tracing where a call tp find_vma() call will be made on a process's context
> to fetch user space's symbols.
> 
> Am I right ?
> Is the find_vma() call made in the context of the process owning the mm
> struct ?

Hi Laurent,

we're thinking about several use cases on top of your work.
First one is translation of user address to file_handle where
we need to do find_vma() from preempt_disabled context of bpf program.
My understanding that srcu should solve that nicely.
Second is making probe_read() to try harder when address is causing
minor fault. We're thinking that find_vma() followed by some new
light weight filemap_access() that doesn't sleep will do the trick.
In both cases the program will be accessing current->mm

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Re: [PATCH v3 00/20] Speculative page faults

[Laurent Dufour]

Despite the unprovable lockdep warning raised by Sergey, I didn't get any
feedback on this series.

Is there a chance to get it moved upstream ?

Thanks,
Laurent.

On 08/09/2017 20:06, Laurent Dufour wrote:
> This is a port on kernel 4.13 of the work done by Peter Zijlstra to
> handle page fault without holding the mm semaphore [1].
> 
> The idea is to try to handle user space page faults without holding the
> mmap_sem. This should allow better concurrency for massively threaded
> process since the page fault handler will not wait for other threads memory
> layout change to be done, assuming that this change is done in another part
> of the process's memory space. This type page fault is named speculative
> page fault. If the speculative page fault fails because of a concurrency is
> detected or because underlying PMD or PTE tables are not yet allocating, it
> is failing its processing and a classic page fault is then tried.
> 
> The speculative page fault (SPF) has to look for the VMA matching the fault
> address without holding the mmap_sem, so the VMA list is now managed using
> SRCU allowing lockless walking. The only impact would be the deferred file
> derefencing in the case of a file mapping, since the file pointer is
> released once the SRCU cleaning is done.  This patch relies on the change
> done recently by Paul McKenney in SRCU which now runs a callback per CPU
> instead of per SRCU structure [1].
> 
> The VMA's attributes checked during the speculative page fault processing
> have to be protected against parallel changes. This is done by using a per
> VMA sequence lock. This sequence lock allows the speculative page fault
> handler to fast check for parallel changes in progress and to abort the
> speculative page fault in that case.
> 
> Once the VMA is found, the speculative page fault handler would check for
> the VMA's attributes to verify that the page fault has to be handled
> correctly or not. Thus the VMA is protected through a sequence lock which
> allows fast detection of concurrent VMA changes. If such a change is
> detected, the speculative page fault is aborted and a *classic* page fault
> is tried.  VMA sequence locks are added when VMA attributes which are
> checked during the page fault are modified.
> 
> When the PTE is fetched, the VMA is checked to see if it has been changed,
> so once the page table is locked, the VMA is valid, so any other changes
> leading to touching this PTE will need to lock the page table, so no
> parallel change is possible at this time.
> 
> Compared to the Peter's initial work, this series introduces a spin_trylock
> when dealing with speculative page fault. This is required to avoid dead
> lock when handling a page fault while a TLB invalidate is requested by an
> other CPU holding the PTE. Another change due to a lock dependency issue
> with mapping->i_mmap_rwsem.
> 
> In addition some VMA field values which are used once the PTE is unlocked
> at the end the page fault path are saved into the vm_fault structure to
> used the values matching the VMA at the time the PTE was locked.
> 
> This series only support VMA with no vm_ops define, so huge page and mapped
> file are not managed with the speculative path. In addition transparent
> huge page are not supported. Once this series will be accepted upstream
> I'll extend the support to mapped files, and transparent huge pages.
> 
> This series builds on top of v4.13.9-mm1 and is functional on x86 and
> PowerPC.
> 
> Tests have been made using a large commercial in-memory database on a
> PowerPC system with 752 CPU using RFC v5 using a previous version of this
> series. The results are very encouraging since the loading of the 2TB
> database was faster by 14% with the speculative page fault.
> 
> Using ebizzy test [3], which spreads a lot of threads, the result are good
> when running on both a large or a small system. When using kernbench, the
> result are quite similar which expected as not so much multithreaded
> processes are involved. But there is no performance degradation neither
> which is good.
> 
> ------------------
> Benchmarks results
> 
> Note these test have been made on top of 4.13.0-mm1.
> 
> Ebizzy:
> -------
> The test is counting the number of records per second it can manage, the
> higher is the best. I run it like this 'ebizzy -mTRp'. To get consistent
> result I repeated the test 100 times and measure the average result, mean
> deviation, max and min.
> 
> - 16 CPUs x86 VM
> Records/s	4.13.0-mm1	4.13.0-mm1-spf	delta
> Average		13217.90 	65765.94	+397.55%
> Mean deviation	690.37		2609.36		+277.97%
> Max		16726		77675		+364.40%
> Min		12194		616340		+405.45%
> 		
> - 80 CPUs Power 8 node:
> Records/s	4.13.0-mm1	4.13.0-mm1-spf	delta
> Average		38175.40	67635.55	77.17% 
> Mean deviation	600.09	 	2349.66		291.55%
> Max		39563		74292		87.78% 
> Min		35846		62657		74.79% 
> 
> The number of record per second is far better with the speculative page
> fault. 
> The mean deviation is higher with the speculative page fault, may be
> because sometime the fault are not handled in a speculative way leading to
> more variation.
> The numbers for the x86 guest are really insane for the SPF case, but I
> did the test several times and this leads each time this delta. I did again
> the test using the previous version of the patch and I got similar
> numbers. It happens that the host running the VM is far less loaded now
> leading to better results as more threads are eligible to run.
> Test on Power are done on a badly balanced node where the memory is only
> attached to one core.
> 
> Kernbench:
> ----------
> This test is building a 4.12 kernel using platform default config. The
> build has been run 5 times each time.
> 
> - 16 CPUs x86 VM
> Average Half load -j 8 Run (std deviation)
>  		 4.13.0-mm1		4.13.0-mm1-spf		delta %
> Elapsed Time     145.968 (0.402206)	145.654 (0.533601)	-0.22
> User Time        1006.58 (2.74729)	1003.7 (4.11294)	-0.29
> System Time      108.464 (0.177567)	111.034 (0.718213)	+2.37
> Percent CPU 	 763.4 (1.34164)	764.8 (1.30384)		+0.18
> Context Switches 46599.6 (412.013)	63771 (1049.95)		+36.85
> Sleeps           85313.2 (514.456)	85532.2 (681.199)	-0.26
> 
> Average Optimal load -j 16 Run (std deviation)
>  		 4.13.0-mm1		4.13.0-mm1-spf		delta %
> Elapsed Time     74.292 (0.75998)	74.484 (0.723035)	+0.26
> User Time        959.949 (49.2036)	956.057 (50.2993)	-0.41
> System Time      100.203 (8.7119)	101.984 (9.56099)	+1.78
> Percent CPU 	 1058 (310.661)		1054.3 (305.263)	-0.35
> Context Switches 65713.8 (20161.7)	86619.4 (24095.4)	+31.81
> Sleeps           90344.9 (5364.74)	90877.4 (5655.87)	-0.59
> 
> The elapsed time are similar, but the impact less important since there are
> less multithreaded processes involved here. 
> 
> - 80 CPUs Power 8 node:
> Average Half load -j 40 Run (std deviation)
> 		 4.13.0-mm1		4.13.0-mm1-spf		delta %
> Elapsed Time 	 115.342 (0.321668)	115.786 (0.427118)	+0.38
> User Time 	 4355.08 (10.1778)	4371.77 (14.9715)	+0.38
> System Time 	 127.612 (0.882083)	130.048 (1.06258)	+1.91
> Percent CPU 	 3885.8 (11.606)	3887.4 (8.04984)	+0.04
> Context Switches 80907.8 (657.481)	81936.4 (729.538)	+1.27
> Sleeps		 162109 (793.331)	162057 (1414.08)	+0.03
> 
> Average Optimal load -j 80 Run (std deviation)
>  		 4.13.0-mm1		4.13.0-mm1-spf
> Elapsed Time 	 110.308 (0.725445)	109.78 (0.826862)	-0.48
> User Time 	 5893.12 (1621.33)	5923.19 (1635.48)	+0.51
> System Time 	 162.168 (36.4347)	166.533 (38.4695)	+2.69
> Percent CPU 	 5400.2 (1596.89)	5440.4 (1637.71)	+0.74
> Context Switches 129372 (51088.2)	144529 (65985.5)	+11.72
> Sleeps		 157312 (5113.57)	158696 (4301.48)	-0.87
> 
> Here the elapsed time are similar the SPF release, but we remain in the error
> margin. It has to be noted that this system is not correctly balanced on
> the NUMA point of view as all the available memory is attached to one core.
> 
> ------------------------
> Changes since v2:
>  - Perf event is renamed in PERF_COUNT_SW_SPF
>  - On Power handle do_page_fault()'s cleaning
>  - On Power if the VM_FAULT_ERROR is returned by
>  handle_speculative_fault(), do not retry but jump to the error path
>  - If VMA's flags are not matching the fault, directly returns
>  VM_FAULT_SIGSEGV and not VM_FAULT_RETRY
>  - Check for pud_trans_huge() to avoid speculative path
>  - Handles _vm_normal_page()'s introduced by 6f16211df3bf
>  ("mm/device-public-memory: device memory cache coherent with CPU")
>  - add and review few comments in the code
> Changes since v1:
>  - Remove PERF_COUNT_SW_SPF_FAILED perf event.
>  - Add tracing events to details speculative page fault failures.
>  - Cache VMA fields values which are used once the PTE is unlocked at the
>  end of the page fault events.
>  - Ensure that fields read during the speculative path are written and read
>  using WRITE_ONCE and READ_ONCE.
>  - Add checks at the beginning of the speculative path to abort it if the
>  VMA is known to not be supported.
> Changes since RFC V5 [5]
>  - Port to 4.13 kernel
>  - Merging patch fixing lock dependency into the original patch
>  - Replace the 2 parameters of vma_has_changed() with the vmf pointer
>  - In patch 7, don't call __do_fault() in the speculative path as it may
>  want to unlock the mmap_sem.
>  - In patch 11-12, don't check for vma boundaries when
>  page_add_new_anon_rmap() is called during the spf path and protect against
>  anon_vma pointer's update.
>  - In patch 13-16, add performance events to report number of successful
>  and failed speculative events. 
> 
> [1] https://urldefense.proofpoint.com/v2/url?u=http-3A__linux-2Dkernel.2935.n7.nabble.com_RFC-2DPATCH-2D0-2D6-2DAnother-2Dgo-2Dat-2Dspeculative-2Dpage-2Dfaults-2Dtt965642.html-23none&d=DwIBAg&c=jf_iaSHvJObTbx-siA1ZOg&r=WE1-GjEMX6XRg4v6rPpC0RVdhh4z63Csy-Wmu5dgUp0&m=449ThuJ31DP_64d96xAqLlSqq4qgY5LlJvzwiULSaos&s=9wDEbeKddqKRa0zfN13yjrErkFIQJo9Ohe07I7IuBSk&e= 
> [2] https://urldefense.proofpoint.com/v2/url?u=https-3A__git.kernel.org_pub_scm_linux_kernel_git_torvalds_linux.git_commit_-3Fid-3Dda915ad5cf25b5f5d358dd3670c3378d8ae8c03e&d=DwIBAg&c=jf_iaSHvJObTbx-siA1ZOg&r=WE1-GjEMX6XRg4v6rPpC0RVdhh4z63Csy-Wmu5dgUp0&m=449ThuJ31DP_64d96xAqLlSqq4qgY5LlJvzwiULSaos&s=OUT_ItjCInfCHdZQS5cjmxUQd3Ws8VkT54MZgJm2dAE&e= 
> [3] https://urldefense.proofpoint.com/v2/url?u=http-3A__ebizzy.sourceforge.net_&d=DwIBAg&c=jf_iaSHvJObTbx-siA1ZOg&r=WE1-GjEMX6XRg4v6rPpC0RVdhh4z63Csy-Wmu5dgUp0&m=449ThuJ31DP_64d96xAqLlSqq4qgY5LlJvzwiULSaos&s=cMZB09rj1TqCKM2B3DPrtrB1LpZan637kvHrM6ShaDk&e= 
> [4] https://urldefense.proofpoint.com/v2/url?u=http-3A__ck.kolivas.org_apps_kernbench_kernbench-2D0.50_&d=DwIBAg&c=jf_iaSHvJObTbx-siA1ZOg&r=WE1-GjEMX6XRg4v6rPpC0RVdhh4z63Csy-Wmu5dgUp0&m=449ThuJ31DP_64d96xAqLlSqq4qgY5LlJvzwiULSaos&s=2D_JH8n0pGF5lE0jSXnb2RY5etKV7C7UfO7-8hknJDE&e= 
> [5] https://urldefense.proofpoint.com/v2/url?u=https-3A__lwn.net_Articles_725607_&d=DwIBAg&c=jf_iaSHvJObTbx-siA1ZOg&r=WE1-GjEMX6XRg4v6rPpC0RVdhh4z63Csy-Wmu5dgUp0&m=449ThuJ31DP_64d96xAqLlSqq4qgY5LlJvzwiULSaos&s=CEgoZjaMNHIZFX-XAzuzr8EswsKhQAArNwmc_8bnduA&e= 
> 
> Laurent Dufour (14):
>   mm: Introduce pte_spinlock for FAULT_FLAG_SPECULATIVE
>   mm: Protect VMA modifications using VMA sequence count
>   mm: Cache some VMA fields in the vm_fault structure
>   mm: Protect SPF handler against anon_vma changes
>   mm/migrate: Pass vm_fault pointer to migrate_misplaced_page()
>   mm: Introduce __lru_cache_add_active_or_unevictable
>   mm: Introduce __maybe_mkwrite()
>   mm: Introduce __vm_normal_page()
>   mm: Introduce __page_add_new_anon_rmap()
>   mm: Try spin lock in speculative path
>   mm: Adding speculative page fault failure trace events
>   perf: Add a speculative page fault sw event
>   perf tools: Add support for the SPF perf event
>   powerpc/mm: Add speculative page fault
> 
> Peter Zijlstra (6):
>   mm: Dont assume page-table invariance during faults
>   mm: Prepare for FAULT_FLAG_SPECULATIVE
>   mm: VMA sequence count
>   mm: RCU free VMAs
>   mm: Provide speculative fault infrastructure
>   x86/mm: Add speculative pagefault handling
> 
>  arch/powerpc/include/asm/book3s/64/pgtable.h |   5 +
>  arch/powerpc/mm/fault.c                      |  15 +
>  arch/x86/include/asm/pgtable_types.h         |   7 +
>  arch/x86/mm/fault.c                          |  19 ++
>  fs/proc/task_mmu.c                           |   5 +-
>  fs/userfaultfd.c                             |  17 +-
>  include/linux/hugetlb_inline.h               |   2 +-
>  include/linux/migrate.h                      |   4 +-
>  include/linux/mm.h                           |  28 +-
>  include/linux/mm_types.h                     |   3 +
>  include/linux/pagemap.h                      |   4 +-
>  include/linux/rmap.h                         |  12 +-
>  include/linux/swap.h                         |  11 +-
>  include/trace/events/pagefault.h             |  87 +++++
>  include/uapi/linux/perf_event.h              |   1 +
>  kernel/fork.c                                |   1 +
>  mm/hugetlb.c                                 |   2 +
>  mm/init-mm.c                                 |   1 +
>  mm/internal.h                                |  19 ++
>  mm/khugepaged.c                              |   5 +
>  mm/madvise.c                                 |   6 +-
>  mm/memory.c                                  | 478 ++++++++++++++++++++++-----
>  mm/mempolicy.c                               |  51 ++-
>  mm/migrate.c                                 |   4 +-
>  mm/mlock.c                                   |  13 +-
>  mm/mmap.c                                    | 138 ++++++--
>  mm/mprotect.c                                |   4 +-
>  mm/mremap.c                                  |   7 +
>  mm/rmap.c                                    |   5 +-
>  mm/swap.c                                    |  12 +-
>  tools/include/uapi/linux/perf_event.h        |   1 +
>  tools/perf/util/evsel.c                      |   1 +
>  tools/perf/util/parse-events.c               |   4 +
>  tools/perf/util/parse-events.l               |   1 +
>  tools/perf/util/python.c                     |   1 +
>  35 files changed, 796 insertions(+), 178 deletions(-)
>  create mode 100644 include/trace/events/pagefault.h
> 

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[PATCH v3 00/20] Speculative page faults

[Laurent Dufour]

This is a port on kernel 4.13 of the work done by Peter Zijlstra to
handle page fault without holding the mm semaphore [1].

The idea is to try to handle user space page faults without holding the
mmap_sem. This should allow better concurrency for massively threaded
process since the page fault handler will not wait for other threads memory
layout change to be done, assuming that this change is done in another part
of the process's memory space. This type page fault is named speculative
page fault. If the speculative page fault fails because of a concurrency is
detected or because underlying PMD or PTE tables are not yet allocating, it
is failing its processing and a classic page fault is then tried.

The speculative page fault (SPF) has to look for the VMA matching the fault
address without holding the mmap_sem, so the VMA list is now managed using
SRCU allowing lockless walking. The only impact would be the deferred file
derefencing in the case of a file mapping, since the file pointer is
released once the SRCU cleaning is done.  This patch relies on the change
done recently by Paul McKenney in SRCU which now runs a callback per CPU
instead of per SRCU structure [1].

The VMA's attributes checked during the speculative page fault processing
have to be protected against parallel changes. This is done by using a per
VMA sequence lock. This sequence lock allows the speculative page fault
handler to fast check for parallel changes in progress and to abort the
speculative page fault in that case.

Once the VMA is found, the speculative page fault handler would check for
the VMA's attributes to verify that the page fault has to be handled
correctly or not. Thus the VMA is protected through a sequence lock which
allows fast detection of concurrent VMA changes. If such a change is
detected, the speculative page fault is aborted and a *classic* page fault
is tried.  VMA sequence locks are added when VMA attributes which are
checked during the page fault are modified.

When the PTE is fetched, the VMA is checked to see if it has been changed,
so once the page table is locked, the VMA is valid, so any other changes
leading to touching this PTE will need to lock the page table, so no
parallel change is possible at this time.

Compared to the Peter's initial work, this series introduces a spin_trylock
when dealing with speculative page fault. This is required to avoid dead
lock when handling a page fault while a TLB invalidate is requested by an
other CPU holding the PTE. Another change due to a lock dependency issue
with mapping->i_mmap_rwsem.

In addition some VMA field values which are used once the PTE is unlocked
at the end the page fault path are saved into the vm_fault structure to
used the values matching the VMA at the time the PTE was locked.

This series only support VMA with no vm_ops define, so huge page and mapped
file are not managed with the speculative path. In addition transparent
huge page are not supported. Once this series will be accepted upstream
I'll extend the support to mapped files, and transparent huge pages.

This series builds on top of v4.13.9-mm1 and is functional on x86 and
PowerPC.

Tests have been made using a large commercial in-memory database on a
PowerPC system with 752 CPU using RFC v5 using a previous version of this
series. The results are very encouraging since the loading of the 2TB
database was faster by 14% with the speculative page fault.

Using ebizzy test [3], which spreads a lot of threads, the result are good
when running on both a large or a small system. When using kernbench, the
result are quite similar which expected as not so much multithreaded
processes are involved. But there is no performance degradation neither
which is good.

------------------
Benchmarks results

Note these test have been made on top of 4.13.0-mm1.

Ebizzy:
-------
The test is counting the number of records per second it can manage, the
higher is the best. I run it like this 'ebizzy -mTRp'. To get consistent
result I repeated the test 100 times and measure the average result, mean
deviation, max and min.

- 16 CPUs x86 VM
Records/s	4.13.0-mm1	4.13.0-mm1-spf	delta
Average		13217.90 	65765.94	+397.55%
Mean deviation	690.37		2609.36		+277.97%
Max		16726		77675		+364.40%
Min		12194		616340		+405.45%
		
- 80 CPUs Power 8 node:
Records/s	4.13.0-mm1	4.13.0-mm1-spf	delta
Average		38175.40	67635.55	77.17% 
Mean deviation	600.09	 	2349.66		291.55%
Max		39563		74292		87.78% 
Min		35846		62657		74.79% 

The number of record per second is far better with the speculative page
fault. 
The mean deviation is higher with the speculative page fault, may be
because sometime the fault are not handled in a speculative way leading to
more variation.
The numbers for the x86 guest are really insane for the SPF case, but I
did the test several times and this leads each time this delta. I did again
the test using the previous version of the patch and I got similar
numbers. It happens that the host running the VM is far less loaded now
leading to better results as more threads are eligible to run.
Test on Power are done on a badly balanced node where the memory is only
attached to one core.

Kernbench:
----------
This test is building a 4.12 kernel using platform default config. The
build has been run 5 times each time.

- 16 CPUs x86 VM
Average Half load -j 8 Run (std deviation)
 		 4.13.0-mm1		4.13.0-mm1-spf		delta %
Elapsed Time     145.968 (0.402206)	145.654 (0.533601)	-0.22
User Time        1006.58 (2.74729)	1003.7 (4.11294)	-0.29
System Time      108.464 (0.177567)	111.034 (0.718213)	+2.37
Percent CPU 	 763.4 (1.34164)	764.8 (1.30384)		+0.18
Context Switches 46599.6 (412.013)	63771 (1049.95)		+36.85
Sleeps           85313.2 (514.456)	85532.2 (681.199)	-0.26

Average Optimal load -j 16 Run (std deviation)
 		 4.13.0-mm1		4.13.0-mm1-spf		delta %
Elapsed Time     74.292 (0.75998)	74.484 (0.723035)	+0.26
User Time        959.949 (49.2036)	956.057 (50.2993)	-0.41
System Time      100.203 (8.7119)	101.984 (9.56099)	+1.78
Percent CPU 	 1058 (310.661)		1054.3 (305.263)	-0.35
Context Switches 65713.8 (20161.7)	86619.4 (24095.4)	+31.81
Sleeps           90344.9 (5364.74)	90877.4 (5655.87)	-0.59

The elapsed time are similar, but the impact less important since there are
less multithreaded processes involved here. 

- 80 CPUs Power 8 node:
Average Half load -j 40 Run (std deviation)
		 4.13.0-mm1		4.13.0-mm1-spf		delta %
Elapsed Time 	 115.342 (0.321668)	115.786 (0.427118)	+0.38
User Time 	 4355.08 (10.1778)	4371.77 (14.9715)	+0.38
System Time 	 127.612 (0.882083)	130.048 (1.06258)	+1.91
Percent CPU 	 3885.8 (11.606)	3887.4 (8.04984)	+0.04
Context Switches 80907.8 (657.481)	81936.4 (729.538)	+1.27
Sleeps		 162109 (793.331)	162057 (1414.08)	+0.03

Average Optimal load -j 80 Run (std deviation)
 		 4.13.0-mm1		4.13.0-mm1-spf
Elapsed Time 	 110.308 (0.725445)	109.78 (0.826862)	-0.48
User Time 	 5893.12 (1621.33)	5923.19 (1635.48)	+0.51
System Time 	 162.168 (36.4347)	166.533 (38.4695)	+2.69
Percent CPU 	 5400.2 (1596.89)	5440.4 (1637.71)	+0.74
Context Switches 129372 (51088.2)	144529 (65985.5)	+11.72
Sleeps		 157312 (5113.57)	158696 (4301.48)	-0.87

Here the elapsed time are similar the SPF release, but we remain in the error
margin. It has to be noted that this system is not correctly balanced on
the NUMA point of view as all the available memory is attached to one core.

------------------------
Changes since v2:
 - Perf event is renamed in PERF_COUNT_SW_SPF
 - On Power handle do_page_fault()'s cleaning
 - On Power if the VM_FAULT_ERROR is returned by
 handle_speculative_fault(), do not retry but jump to the error path
 - If VMA's flags are not matching the fault, directly returns
 VM_FAULT_SIGSEGV and not VM_FAULT_RETRY
 - Check for pud_trans_huge() to avoid speculative path
 - Handles _vm_normal_page()'s introduced by 6f16211df3bf
 ("mm/device-public-memory: device memory cache coherent with CPU")
 - add and review few comments in the code
Changes since v1:
 - Remove PERF_COUNT_SW_SPF_FAILED perf event.
 - Add tracing events to details speculative page fault failures.
 - Cache VMA fields values which are used once the PTE is unlocked at the
 end of the page fault events.
 - Ensure that fields read during the speculative path are written and read
 using WRITE_ONCE and READ_ONCE.
 - Add checks at the beginning of the speculative path to abort it if the
 VMA is known to not be supported.
Changes since RFC V5 [5]
 - Port to 4.13 kernel
 - Merging patch fixing lock dependency into the original patch
 - Replace the 2 parameters of vma_has_changed() with the vmf pointer
 - In patch 7, don't call __do_fault() in the speculative path as it may
 want to unlock the mmap_sem.
 - In patch 11-12, don't check for vma boundaries when
 page_add_new_anon_rmap() is called during the spf path and protect against
 anon_vma pointer's update.
 - In patch 13-16, add performance events to report number of successful
 and failed speculative events. 

[1] http://linux-kernel.2935.n7.nabble.com/RFC-PATCH-0-6-Another-go-at-speculative-page-faults-tt965642.html#none
[2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=da915ad5cf25b5f5d358dd3670c3378d8ae8c03e
[3] http://ebizzy.sourceforge.net/
[4] http://ck.kolivas.org/apps/kernbench/kernbench-0.50/
[5] https://lwn.net/Articles/725607/

Laurent Dufour (14):
  mm: Introduce pte_spinlock for FAULT_FLAG_SPECULATIVE
  mm: Protect VMA modifications using VMA sequence count
  mm: Cache some VMA fields in the vm_fault structure
  mm: Protect SPF handler against anon_vma changes
  mm/migrate: Pass vm_fault pointer to migrate_misplaced_page()
  mm: Introduce __lru_cache_add_active_or_unevictable
  mm: Introduce __maybe_mkwrite()
  mm: Introduce __vm_normal_page()
  mm: Introduce __page_add_new_anon_rmap()
  mm: Try spin lock in speculative path
  mm: Adding speculative page fault failure trace events
  perf: Add a speculative page fault sw event
  perf tools: Add support for the SPF perf event
  powerpc/mm: Add speculative page fault

Peter Zijlstra (6):
  mm: Dont assume page-table invariance during faults
  mm: Prepare for FAULT_FLAG_SPECULATIVE
  mm: VMA sequence count
  mm: RCU free VMAs
  mm: Provide speculative fault infrastructure
  x86/mm: Add speculative pagefault handling

 arch/powerpc/include/asm/book3s/64/pgtable.h |   5 +
 arch/powerpc/mm/fault.c                      |  15 +
 arch/x86/include/asm/pgtable_types.h         |   7 +
 arch/x86/mm/fault.c                          |  19 ++
 fs/proc/task_mmu.c                           |   5 +-
 fs/userfaultfd.c                             |  17 +-
 include/linux/hugetlb_inline.h               |   2 +-
 include/linux/migrate.h                      |   4 +-
 include/linux/mm.h                           |  28 +-
 include/linux/mm_types.h                     |   3 +
 include/linux/pagemap.h                      |   4 +-
 include/linux/rmap.h                         |  12 +-
 include/linux/swap.h                         |  11 +-
 include/trace/events/pagefault.h             |  87 +++++
 include/uapi/linux/perf_event.h              |   1 +
 kernel/fork.c                                |   1 +
 mm/hugetlb.c                                 |   2 +
 mm/init-mm.c                                 |   1 +
 mm/internal.h                                |  19 ++
 mm/khugepaged.c                              |   5 +
 mm/madvise.c                                 |   6 +-
 mm/memory.c                                  | 478 ++++++++++++++++++++++-----
 mm/mempolicy.c                               |  51 ++-
 mm/migrate.c                                 |   4 +-
 mm/mlock.c                                   |  13 +-
 mm/mmap.c                                    | 138 ++++++--
 mm/mprotect.c                                |   4 +-
 mm/mremap.c                                  |   7 +
 mm/rmap.c                                    |   5 +-
 mm/swap.c                                    |  12 +-
 tools/include/uapi/linux/perf_event.h        |   1 +
 tools/perf/util/evsel.c                      |   1 +
 tools/perf/util/parse-events.c               |   4 +
 tools/perf/util/parse-events.l               |   1 +
 tools/perf/util/python.c                     |   1 +
 35 files changed, 796 insertions(+), 178 deletions(-)
 create mode 100644 include/trace/events/pagefault.h

-- 
2.7.4

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Re: [PATCH v3 00/20] Speculative page faults

[Laurent Dufour]

On 08/09/2017 19:32, Laurent Dufour wrote:
> This is a port on kernel 4.13 of the work done by Peter Zijlstra to
> handle page fault without holding the mm semaphore [1].

Sorry for the noise, I got trouble sending the whole series through this
email. I will try again.

Cheers,
Laurent.

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[PATCH v3 00/20] Speculative page faults

[Laurent Dufour]

This is a port on kernel 4.13 of the work done by Peter Zijlstra to
handle page fault without holding the mm semaphore [1].

The idea is to try to handle user space page faults without holding the
mmap_sem. This should allow better concurrency for massively threaded
process since the page fault handler will not wait for other threads memory
layout change to be done, assuming that this change is done in another part
of the process's memory space. This type page fault is named speculative
page fault. If the speculative page fault fails because of a concurrency is
detected or because underlying PMD or PTE tables are not yet allocating, it
is failing its processing and a classic page fault is then tried.

The speculative page fault (SPF) has to look for the VMA matching the fault
address without holding the mmap_sem, so the VMA list is now managed using
SRCU allowing lockless walking. The only impact would be the deferred file
derefencing in the case of a file mapping, since the file pointer is
released once the SRCU cleaning is done.  This patch relies on the change
done recently by Paul McKenney in SRCU which now runs a callback per CPU
instead of per SRCU structure [1].

The VMA's attributes checked during the speculative page fault processing
have to be protected against parallel changes. This is done by using a per
VMA sequence lock. This sequence lock allows the speculative page fault
handler to fast check for parallel changes in progress and to abort the
speculative page fault in that case.

Once the VMA is found, the speculative page fault handler would check for
the VMA's attributes to verify that the page fault has to be handled
correctly or not. Thus the VMA is protected through a sequence lock which
allows fast detection of concurrent VMA changes. If such a change is
detected, the speculative page fault is aborted and a *classic* page fault
is tried.  VMA sequence locks are added when VMA attributes which are
checked during the page fault are modified.

When the PTE is fetched, the VMA is checked to see if it has been changed,
so once the page table is locked, the VMA is valid, so any other changes
leading to touching this PTE will need to lock the page table, so no
parallel change is possible at this time.

Compared to the Peter's initial work, this series introduces a spin_trylock
when dealing with speculative page fault. This is required to avoid dead
lock when handling a page fault while a TLB invalidate is requested by an
other CPU holding the PTE. Another change due to a lock dependency issue
with mapping->i_mmap_rwsem.

In addition some VMA field values which are used once the PTE is unlocked
at the end the page fault path are saved into the vm_fault structure to
used the values matching the VMA at the time the PTE was locked.

This series only support VMA with no vm_ops define, so huge page and mapped
file are not managed with the speculative path. In addition transparent
huge page are not supported. Once this series will be accepted upstream
I'll extend the support to mapped files, and transparent huge pages.

This series builds on top of v4.13.9-mm1 and is functional on x86 and
PowerPC.

Tests have been made using a large commercial in-memory database on a
PowerPC system with 752 CPU using RFC v5 using a previous version of this
series. The results are very encouraging since the loading of the 2TB
database was faster by 14% with the speculative page fault.

Using ebizzy test [3], which spreads a lot of threads, the result are good
when running on both a large or a small system. When using kernbench, the
result are quite similar which expected as not so much multithreaded
processes are involved. But there is no performance degradation neither
which is good.

------------------
Benchmarks results

Note these test have been made on top of 4.13.0-mm1.

Ebizzy:
-------
The test is counting the number of records per second it can manage, the
higher is the best. I run it like this 'ebizzy -mTRp'. To get consistent
result I repeated the test 100 times and measure the average result, mean
deviation, max and min.

- 16 CPUs x86 VM
Records/s	4.13.0-mm1	4.13.0-mm1-spf	delta
Average		13217.90 	65765.94	+397.55%
Mean deviation	690.37		2609.36		+277.97%
Max		16726		77675		+364.40%
Min		12194		616340		+405.45%
		
- 80 CPUs Power 8 node:
Records/s	4.13.0-mm1	4.13.0-mm1-spf	delta
Average		38175.40	67635.55	77.17% 
Mean deviation	600.09	 	2349.66		291.55%
Max		39563		74292		87.78% 
Min		35846		62657		74.79% 

The number of record per second is far better with the speculative page
fault. 
The mean deviation is higher with the speculative page fault, may be
because sometime the fault are not handled in a speculative way leading to
more variation.
The numbers for the x86 guest are really insane for the SPF case, but I
did the test several times and this leads each time this delta. I did again
the test using the previous version of the patch and I got similar
numbers. It happens that the host running the VM is far less loaded now
leading to better results as more threads are eligible to run.
Test on Power are done on a badly balanced node where the memory is only
attached to one core.

Kernbench:
----------
This test is building a 4.12 kernel using platform default config. The
build has been run 5 times each time.

- 16 CPUs x86 VM
Average Half load -j 8 Run (std deviation)
 		 4.13.0-mm1		4.13.0-mm1-spf		delta %
Elapsed Time     145.968 (0.402206)	145.654 (0.533601)	-0.22
User Time        1006.58 (2.74729)	1003.7 (4.11294)	-0.29
System Time      108.464 (0.177567)	111.034 (0.718213)	+2.37
Percent CPU 	 763.4 (1.34164)	764.8 (1.30384)		+0.18
Context Switches 46599.6 (412.013)	63771 (1049.95)		+36.85
Sleeps           85313.2 (514.456)	85532.2 (681.199)	-0.26

Average Optimal load -j 16 Run (std deviation)
 		 4.13.0-mm1		4.13.0-mm1-spf		delta %
Elapsed Time     74.292 (0.75998)	74.484 (0.723035)	+0.26
User Time        959.949 (49.2036)	956.057 (50.2993)	-0.41
System Time      100.203 (8.7119)	101.984 (9.56099)	+1.78
Percent CPU 	 1058 (310.661)		1054.3 (305.263)	-0.35
Context Switches 65713.8 (20161.7)	86619.4 (24095.4)	+31.81
Sleeps           90344.9 (5364.74)	90877.4 (5655.87)	-0.59

The elapsed time are similar, but the impact less important since there are
less multithreaded processes involved here. 

- 80 CPUs Power 8 node:
Average Half load -j 40 Run (std deviation)
		 4.13.0-mm1		4.13.0-mm1-spf		delta %
Elapsed Time 	 115.342 (0.321668)	115.786 (0.427118)	+0.38
User Time 	 4355.08 (10.1778)	4371.77 (14.9715)	+0.38
System Time 	 127.612 (0.882083)	130.048 (1.06258)	+1.91
Percent CPU 	 3885.8 (11.606)	3887.4 (8.04984)	+0.04
Context Switches 80907.8 (657.481)	81936.4 (729.538)	+1.27
Sleeps		 162109 (793.331)	162057 (1414.08)	+0.03

Average Optimal load -j 80 Run (std deviation)
 		 4.13.0-mm1		4.13.0-mm1-spf
Elapsed Time 	 110.308 (0.725445)	109.78 (0.826862)	-0.48
User Time 	 5893.12 (1621.33)	5923.19 (1635.48)	+0.51
System Time 	 162.168 (36.4347)	166.533 (38.4695)	+2.69
Percent CPU 	 5400.2 (1596.89)	5440.4 (1637.71)	+0.74
Context Switches 129372 (51088.2)	144529 (65985.5)	+11.72
Sleeps		 157312 (5113.57)	158696 (4301.48)	-0.87

Here the elapsed time are similar the SPF release, but we remain in the error
margin. It has to be noted that this system is not correctly balanced on
the NUMA point of view as all the available memory is attached to one core.

------------------------
Changes since v2:
 - Perf event is renamed in PERF_COUNT_SW_SPF
 - On Power handle do_page_fault()'s cleaning
 - On Power if the VM_FAULT_ERROR is returned by
 handle_speculative_fault(), do not retry but jump to the error path
 - If VMA's flags are not matching the fault, directly returns
 VM_FAULT_SIGSEGV and not VM_FAULT_RETRY
 - Check for pud_trans_huge() to avoid speculative path
 - Handles _vm_normal_page()'s introduced by 6f16211df3bf
 ("mm/device-public-memory: device memory cache coherent with CPU")
 - add and review few comments in the code
Changes since v1:
 - Remove PERF_COUNT_SW_SPF_FAILED perf event.
 - Add tracing events to details speculative page fault failures.
 - Cache VMA fields values which are used once the PTE is unlocked at the
 end of the page fault events.
 - Ensure that fields read during the speculative path are written and read
 using WRITE_ONCE and READ_ONCE.
 - Add checks at the beginning of the speculative path to abort it if the
 VMA is known to not be supported.
Changes since RFC V5 [5]
 - Port to 4.13 kernel
 - Merging patch fixing lock dependency into the original patch
 - Replace the 2 parameters of vma_has_changed() with the vmf pointer
 - In patch 7, don't call __do_fault() in the speculative path as it may
 want to unlock the mmap_sem.
 - In patch 11-12, don't check for vma boundaries when
 page_add_new_anon_rmap() is called during the spf path and protect against
 anon_vma pointer's update.
 - In patch 13-16, add performance events to report number of successful
 and failed speculative events. 

[1] http://linux-kernel.2935.n7.nabble.com/RFC-PATCH-0-6-Another-go-at-speculative-page-faults-tt965642.html#none
[2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=da915ad5cf25b5f5d358dd3670c3378d8ae8c03e
[3] http://ebizzy.sourceforge.net/
[4] http://ck.kolivas.org/apps/kernbench/kernbench-0.50/
[5] https://lwn.net/Articles/725607/

Laurent Dufour (14):
  mm: Introduce pte_spinlock for FAULT_FLAG_SPECULATIVE
  mm: Protect VMA modifications using VMA sequence count
  mm: Cache some VMA fields in the vm_fault structure
  mm: Protect SPF handler against anon_vma changes
  mm/migrate: Pass vm_fault pointer to migrate_misplaced_page()
  mm: Introduce __lru_cache_add_active_or_unevictable
  mm: Introduce __maybe_mkwrite()
  mm: Introduce __vm_normal_page()
  mm: Introduce __page_add_new_anon_rmap()
  mm: Try spin lock in speculative path
  mm: Adding speculative page fault failure trace events
  perf: Add a speculative page fault sw event
  perf tools: Add support for the SPF perf event
  powerpc/mm: Add speculative page fault

Peter Zijlstra (6):
  mm: Dont assume page-table invariance during faults
  mm: Prepare for FAULT_FLAG_SPECULATIVE
  mm: VMA sequence count
  mm: RCU free VMAs
  mm: Provide speculative fault infrastructure
  x86/mm: Add speculative pagefault handling

 arch/powerpc/include/asm/book3s/64/pgtable.h |   5 +
 arch/powerpc/mm/fault.c                      |  15 +
 arch/x86/include/asm/pgtable_types.h         |   7 +
 arch/x86/mm/fault.c                          |  19 ++
 fs/proc/task_mmu.c                           |   5 +-
 fs/userfaultfd.c                             |  17 +-
 include/linux/hugetlb_inline.h               |   2 +-
 include/linux/migrate.h                      |   4 +-
 include/linux/mm.h                           |  28 +-
 include/linux/mm_types.h                     |   3 +
 include/linux/pagemap.h                      |   4 +-
 include/linux/rmap.h                         |  12 +-
 include/linux/swap.h                         |  11 +-
 include/trace/events/pagefault.h             |  87 +++++
 include/uapi/linux/perf_event.h              |   1 +
 kernel/fork.c                                |   1 +
 mm/hugetlb.c                                 |   2 +
 mm/init-mm.c                                 |   1 +
 mm/internal.h                                |  19 ++
 mm/khugepaged.c                              |   5 +
 mm/madvise.c                                 |   6 +-
 mm/memory.c                                  | 478 ++++++++++++++++++++++-----
 mm/mempolicy.c                               |  51 ++-
 mm/migrate.c                                 |   4 +-
 mm/mlock.c                                   |  13 +-
 mm/mmap.c                                    | 138 ++++++--
 mm/mprotect.c                                |   4 +-
 mm/mremap.c                                  |   7 +
 mm/rmap.c                                    |   5 +-
 mm/swap.c                                    |  12 +-
 tools/include/uapi/linux/perf_event.h        |   1 +
 tools/perf/util/evsel.c                      |   1 +
 tools/perf/util/parse-events.c               |   4 +
 tools/perf/util/parse-events.l               |   1 +
 tools/perf/util/python.c                     |   1 +
 35 files changed, 796 insertions(+), 178 deletions(-)
 create mode 100644 include/trace/events/pagefault.h

-- 
2.7.4

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