Re: [PATCH v11 00/26] Speculative page faults

[Laurent Dufour <ldufour@linux.vnet.ibm.com>]

On 11/06/2018 09:49, Song, HaiyanX wrote:
> Hi Laurent,
> 
> Regression test for v11 patch serials have been run, some regression is found by LKP-tools (linux kernel performance)
> tested on Intel 4s skylake platform. This time only test the cases which have been run and found regressions on
> V9 patch serials.
> 
> The regression result is sorted by the metric will-it-scale.per_thread_ops.
> branch: Laurent-Dufour/Speculative-page-faults/20180520-045126
> commit id:
>   head commit : a7a8993bfe3ccb54ad468b9f1799649e4ad1ff12
>   base commit : ba98a1cdad71d259a194461b3a61471b49b14df1
> Benchmark: will-it-scale
> Download link: https://github.com/antonblanchard/will-it-scale/tree/master
> 
> Metrics:
>   will-it-scale.per_process_ops=processes/nr_cpu
>   will-it-scale.per_thread_ops=threads/nr_cpu
>   test box: lkp-skl-4sp1(nr_cpu=192,memory=768G)
> THP: enable / disable
> nr_task:100%
> 
> 1. Regressions:
> 
> a). Enable THP
> testcase                          base           change      head           metric
> page_fault3/enable THP           10519          -20.5%        836      will-it-scale.per_thread_ops
> page_fault2/enalbe THP            8281          -18.8%       6728      will-it-scale.per_thread_ops
> brk1/eanble THP                 998475           -2.2%     976893      will-it-scale.per_process_ops
> context_switch1/enable THP      223910           -1.3%     220930      will-it-scale.per_process_ops
> context_switch1/enable THP      233722           -1.0%     231288      will-it-scale.per_thread_ops
> 
> b). Disable THP
> page_fault3/disable THP          10856          -23.1%       8344      will-it-scale.per_thread_ops
> page_fault2/disable THP           8147          -18.8%       6613      will-it-scale.per_thread_ops
> brk1/disable THP                   957           -7.9%        881      will-it-scale.per_thread_ops
> context_switch1/disable THP     237006           -2.2%     231907      will-it-scale.per_thread_ops
> brk1/disable THP                997317           -2.0%     977778      will-it-scale.per_process_ops
> page_fault3/disable THP         467454           -1.8%     459251      will-it-scale.per_process_ops
> context_switch1/disable THP     224431           -1.3%     221567      will-it-scale.per_process_ops
> 
> Notes: for the above  values of test result, the higher is better.

I tried the same tests on my PowerPC victim VM (1024 CPUs, 11TB) and I can't
get reproducible results. The results have huge variation, even on the vanilla
kernel, and I can't state on any changes due to that.

I tried on smaller node (80 CPUs, 32G), and the tests ran better, but I didn't
measure any changes between the vanilla and the SPF patched ones:

test THP enabled		4.17.0-rc4-mm1	spf		delta
page_fault3_threads		2697.7		2683.5		-0.53%
page_fault2_threads		170660.6	169574.1	-0.64%
context_switch1_threads		6915269.2	6877507.3	-0.55%
context_switch1_processes	6478076.2	6529493.5	0.79%
brk1				243391.2	238527.5	-2.00%

Tests were run 10 times, no high variation detected.

Did you see high variation on your side ? How many times the test were run to
compute the average values ?

Thanks,
Laurent.


> 
> 2. Improvement: not found improvement based on the selected test cases.
> 
> 
> Best regards
> Haiyan Song
> ________________________________________
> From: owner-linux-mm@kvack.org [owner-linux-mm@kvack.org] on behalf of Laurent Dufour [ldufour@linux.vnet.ibm.com]
> Sent: Monday, May 28, 2018 4:54 PM
> To: Song, HaiyanX
> Cc: akpm@linux-foundation.org; mhocko@kernel.org; peterz@infradead.org; kirill@shutemov.name; ak@linux.intel.com; dave@stgolabs.net; jack@suse.cz; Matthew Wilcox; khandual@linux.vnet.ibm.com; aneesh.kumar@linux.vnet.ibm.com; benh@kernel.crashing.org; mpe@ellerman.id.au; paulus@samba.org; Thomas Gleixner; Ingo Molnar; hpa@zytor.com; Will Deacon; Sergey Senozhatsky; sergey.senozhatsky.work@gmail.com; Andrea Arcangeli; Alexei Starovoitov; Wang, Kemi; Daniel Jordan; David Rientjes; Jerome Glisse; Ganesh Mahendran; Minchan Kim; Punit Agrawal; vinayak menon; Yang Shi; linux-kernel@vger.kernel.org; linux-mm@kvack.org; haren@linux.vnet.ibm.com; npiggin@gmail.com; bsingharora@gmail.com; paulmck@linux.vnet.ibm.com; Tim Chen; linuxppc-dev@lists.ozlabs.org; x86@kernel.org
> Subject: Re: [PATCH v11 00/26] Speculative page faults
> 
> On 28/05/2018 10:22, Haiyan Song wrote:
>> Hi Laurent,
>>
>> Yes, these tests are done on V9 patch.
> 
> Do you plan to give this V11 a run ?
> 
>>
>>
>> Best regards,
>> Haiyan Song
>>
>> On Mon, May 28, 2018 at 09:51:34AM +0200, Laurent Dufour wrote:
>>> On 28/05/2018 07:23, Song, HaiyanX wrote:
>>>>
>>>> Some regression and improvements is found by LKP-tools(linux kernel performance) on V9 patch series
>>>> tested on Intel 4s Skylake platform.
>>>
>>> Hi,
>>>
>>> Thanks for reporting this benchmark results, but you mentioned the "V9 patch
>>> series" while responding to the v11 header series...
>>> Were these tests done on v9 or v11 ?
>>>
>>> Cheers,
>>> Laurent.
>>>
>>>>
>>>> The regression result is sorted by the metric will-it-scale.per_thread_ops.
>>>> Branch: Laurent-Dufour/Speculative-page-faults/20180316-151833 (V9 patch series)
>>>> Commit id:
>>>>     base commit: d55f34411b1b126429a823d06c3124c16283231f
>>>>     head commit: 0355322b3577eeab7669066df42c550a56801110
>>>> Benchmark suite: will-it-scale
>>>> Download link:
>>>> https://github.com/antonblanchard/will-it-scale/tree/master/tests
>>>> Metrics:
>>>>     will-it-scale.per_process_ops=processes/nr_cpu
>>>>     will-it-scale.per_thread_ops=threads/nr_cpu
>>>> test box: lkp-skl-4sp1(nr_cpu=192,memory=768G)
>>>> THP: enable / disable
>>>> nr_task: 100%
>>>>
>>>> 1. Regressions:
>>>> a) THP enabled:
>>>> testcase                        base            change          head       metric
>>>> page_fault3/ enable THP         10092           -17.5%          8323       will-it-scale.per_thread_ops
>>>> page_fault2/ enable THP          8300           -17.2%          6869       will-it-scale.per_thread_ops
>>>> brk1/ enable THP                  957.67         -7.6%           885       will-it-scale.per_thread_ops
>>>> page_fault3/ enable THP        172821            -5.3%        163692       will-it-scale.per_process_ops
>>>> signal1/ enable THP              9125            -3.2%          8834       will-it-scale.per_process_ops
>>>>
>>>> b) THP disabled:
>>>> testcase                        base            change          head       metric
>>>> page_fault3/ disable THP        10107           -19.1%          8180       will-it-scale.per_thread_ops
>>>> page_fault2/ disable THP         8432           -17.8%          6931       will-it-scale.per_thread_ops
>>>> context_switch1/ disable THP   215389            -6.8%        200776       will-it-scale.per_thread_ops
>>>> brk1/ disable THP                 939.67         -6.6%           877.33    will-it-scale.per_thread_ops
>>>> page_fault3/ disable THP       173145            -4.7%        165064       will-it-scale.per_process_ops
>>>> signal1/ disable THP             9162            -3.9%          8802       will-it-scale.per_process_ops
>>>>
>>>> 2. Improvements:
>>>> a) THP enabled:
>>>> testcase                        base            change          head       metric
>>>> malloc1/ enable THP               66.33        +469.8%           383.67    will-it-scale.per_thread_ops
>>>> writeseek3/ enable THP          2531             +4.5%          2646       will-it-scale.per_thread_ops
>>>> signal1/ enable THP              989.33          +2.8%          1016       will-it-scale.per_thread_ops
>>>>
>>>> b) THP disabled:
>>>> testcase                        base            change          head       metric
>>>> malloc1/ disable THP              90.33        +417.3%           467.33    will-it-scale.per_thread_ops
>>>> read2/ disable THP             58934            +39.2%         82060       will-it-scale.per_thread_ops
>>>> page_fault1/ disable THP        8607            +36.4%         11736       will-it-scale.per_thread_ops
>>>> read1/ disable THP            314063            +12.7%        353934       will-it-scale.per_thread_ops
>>>> writeseek3/ disable THP         2452            +12.5%          2759       will-it-scale.per_thread_ops
>>>> signal1/ disable THP             971.33          +5.5%          1024       will-it-scale.per_thread_ops
>>>>
>>>> Notes: for above values in column "change", the higher value means that the related testcase result
>>>> on head commit is better than that on base commit for this benchmark.
>>>>
>>>>
>>>> Best regards
>>>> Haiyan Song
>>>>
>>>> ________________________________________
>>>> From: owner-linux-mm@kvack.org [owner-linux-mm@kvack.org] on behalf of Laurent Dufour [ldufour@linux.vnet.ibm.com]
>>>> Sent: Thursday, May 17, 2018 7:06 PM
>>>> To: akpm@linux-foundation.org; mhocko@kernel.org; peterz@infradead.org; kirill@shutemov.name; ak@linux.intel.com; dave@stgolabs.net; jack@suse.cz; Matthew Wilcox; khandual@linux.vnet.ibm.com; aneesh.kumar@linux.vnet.ibm.com; benh@kernel.crashing.org; mpe@ellerman.id.au; paulus@samba.org; Thomas Gleixner; Ingo Molnar; hpa@zytor.com; Will Deacon; Sergey Senozhatsky; sergey.senozhatsky.work@gmail.com; Andrea Arcangeli; Alexei Starovoitov; Wang, Kemi; Daniel Jordan; David Rientjes; Jerome Glisse; Ganesh Mahendran; Minchan Kim; Punit Agrawal; vinayak menon; Yang Shi
>>>> Cc: linux-kernel@vger.kernel.org; linux-mm@kvack.org; haren@linux.vnet.ibm.com; npiggin@gmail.com; bsingharora@gmail.com; paulmck@linux.vnet.ibm.com; Tim Chen; linuxppc-dev@lists.ozlabs.org; x86@kernel.org
>>>> Subject: [PATCH v11 00/26] Speculative page faults
>>>>
>>>> This is a port on kernel 4.17 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, this is done by introducing a rwlock
>>>> which protects the access to the mm_rb tree. Previously this was done using
>>>> SRCU but it was introducing a lot of scheduling to process the VMA's
>>>> freeing operation which was hitting the performance by 20% as reported by
>>>> Kemi Wang [2]. Using a rwlock to protect access to the mm_rb tree is
>>>> limiting the locking contention to these operations which are expected to
>>>> be in a O(log n) order. In addition to ensure that the VMA is not freed in
>>>> our back a reference count is added and 2 services (get_vma() and
>>>> put_vma()) are introduced to handle the reference count. Once a VMA is
>>>> fetched from the RB tree using get_vma(), it must be later freed using
>>>> put_vma(). I can't see anymore the overhead I got while will-it-scale
>>>> benchmark anymore.
>>>>
>>>> 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 has been 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 lockings 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.
>>>>
>>>> The locking of the PTE is done with interrupts disabled, this allows
>>>> checking for the PMD to ensure that there is not an ongoing collapsing
>>>> operation. Since khugepaged is firstly set the PMD to pmd_none and then is
>>>> waiting for the other CPU to have caught the IPI interrupt, if the pmd is
>>>> valid at the time the PTE is locked, we have the guarantee that the
>>>> collapsing operation will have to wait on the PTE lock to move forward.
>>>> This allows the SPF handler to map the PTE safely. If the PMD value is
>>>> different from the one recorded at the beginning of the SPF operation, the
>>>> classic page fault handler will be called to handle the operation while
>>>> holding the mmap_sem. As the PTE lock is done with the interrupts disabled,
>>>> the lock is done using spin_trylock() to avoid dead lock when handling a
>>>> page fault while a TLB invalidate is requested by another CPU holding the
>>>> PTE.
>>>>
>>>> In pseudo code, this could be seen as:
>>>>     speculative_page_fault()
>>>>     {
>>>>             vma = get_vma()
>>>>             check vma sequence count
>>>>             check vma's support
>>>>             disable interrupt
>>>>                   check pgd,p4d,...,pte
>>>>                   save pmd and pte in vmf
>>>>                   save vma sequence counter in vmf
>>>>             enable interrupt
>>>>             check vma sequence count
>>>>             handle_pte_fault(vma)
>>>>                     ..
>>>>                     page = alloc_page()
>>>>                     pte_map_lock()
>>>>                             disable interrupt
>>>>                                     abort if sequence counter has changed
>>>>                                     abort if pmd or pte has changed
>>>>                                     pte map and lock
>>>>                             enable interrupt
>>>>                     if abort
>>>>                        free page
>>>>                        abort
>>>>                     ...
>>>>     }
>>>>
>>>>     arch_fault_handler()
>>>>     {
>>>>             if (speculative_page_fault(&vma))
>>>>                goto done
>>>>     again:
>>>>             lock(mmap_sem)
>>>>             vma = find_vma();
>>>>             handle_pte_fault(vma);
>>>>             if retry
>>>>                unlock(mmap_sem)
>>>>                goto again;
>>>>     done:
>>>>             handle fault error
>>>>     }
>>>>
>>>> Support for THP is not done because when checking for the PMD, we can be
>>>> confused by an in progress collapsing operation done by khugepaged. The
>>>> issue is that pmd_none() could be true either if the PMD is not already
>>>> populated or if the underlying PTE are in the way to be collapsed. So we
>>>> cannot safely allocate a PMD if pmd_none() is true.
>>>>
>>>> This series add a new software performance event named 'speculative-faults'
>>>> or 'spf'. It counts the number of successful page fault event handled
>>>> speculatively. When recording 'faults,spf' events, the faults one is
>>>> counting the total number of page fault events while 'spf' is only counting
>>>> the part of the faults processed speculatively.
>>>>
>>>> There are some trace events introduced by this series. They allow
>>>> identifying why the page faults were not processed speculatively. This
>>>> doesn't take in account the faults generated by a monothreaded process
>>>> which directly processed while holding the mmap_sem. This trace events are
>>>> grouped in a system named 'pagefault', they are:
>>>>  - pagefault:spf_vma_changed : if the VMA has been changed in our back
>>>>  - pagefault:spf_vma_noanon : the vma->anon_vma field was not yet set.
>>>>  - pagefault:spf_vma_notsup : the VMA's type is not supported
>>>>  - pagefault:spf_vma_access : the VMA's access right are not respected
>>>>  - pagefault:spf_pmd_changed : the upper PMD pointer has changed in our
>>>>    back.
>>>>
>>>> To record all the related events, the easier is to run perf with the
>>>> following arguments :
>>>> $ perf stat -e 'faults,spf,pagefault:*' <command>
>>>>
>>>> There is also a dedicated vmstat counter showing the number of successful
>>>> page fault handled speculatively. I can be seen this way:
>>>> $ grep speculative_pgfault /proc/vmstat
>>>>
>>>> This series builds on top of v4.16-mmotm-2018-04-13-17-28 and is functional
>>>> on x86, PowerPC and arm64.
>>>>
>>>> ---------------------
>>>> Real Workload results
>>>>
>>>> As mentioned in previous email, we did non official runs using a "popular
>>>> in memory multithreaded database product" on 176 cores SMT8 Power system
>>>> which showed a 30% improvements in the number of transaction processed per
>>>> second. This run has been done on the v6 series, but changes introduced in
>>>> this new version should not impact the performance boost seen.
>>>>
>>>> Here are the perf data captured during 2 of these runs on top of the v8
>>>> series:
>>>>                 vanilla         spf
>>>> faults          89.418          101.364         +13%
>>>> spf                n/a           97.989
>>>>
>>>> With the SPF kernel, most of the page fault were processed in a speculative
>>>> way.
>>>>
>>>> Ganesh Mahendran had backported the series on top of a 4.9 kernel and gave
>>>> it a try on an android device. He reported that the application launch time
>>>> was improved in average by 6%, and for large applications (~100 threads) by
>>>> 20%.
>>>>
>>>> Here are the launch time Ganesh mesured on Android 8.0 on top of a Qcom
>>>> MSM845 (8 cores) with 6GB (the less is better):
>>>>
>>>> Application                             4.9     4.9+spf delta
>>>> com.tencent.mm                          416     389     -7%
>>>> com.eg.android.AlipayGphone             1135    986     -13%
>>>> com.tencent.mtt                         455     454     0%
>>>> com.qqgame.hlddz                        1497    1409    -6%
>>>> com.autonavi.minimap                    711     701     -1%
>>>> com.tencent.tmgp.sgame                  788     748     -5%
>>>> com.immomo.momo                         501     487     -3%
>>>> com.tencent.peng                        2145    2112    -2%
>>>> com.smile.gifmaker                      491     461     -6%
>>>> com.baidu.BaiduMap                      479     366     -23%
>>>> com.taobao.taobao                       1341    1198    -11%
>>>> com.baidu.searchbox                     333     314     -6%
>>>> com.tencent.mobileqq                    394     384     -3%
>>>> com.sina.weibo                          907     906     0%
>>>> com.youku.phone                         816     731     -11%
>>>> com.happyelements.AndroidAnimal.qq      763     717     -6%
>>>> com.UCMobile                            415     411     -1%
>>>> com.tencent.tmgp.ak                     1464    1431    -2%
>>>> com.tencent.qqmusic                     336     329     -2%
>>>> com.sankuai.meituan                     1661    1302    -22%
>>>> com.netease.cloudmusic                  1193    1200    1%
>>>> air.tv.douyu.android                    4257    4152    -2%
>>>>
>>>> ------------------
>>>> Benchmarks results
>>>>
>>>> Base kernel is v4.17.0-rc4-mm1
>>>> SPF is BASE + this series
>>>>
>>>> Kernbench:
>>>> ----------
>>>> Here are the results on a 16 CPUs X86 guest using kernbench on a 4.15
>>>> kernel (kernel is build 5 times):
>>>>
>>>> Average Half load -j 8
>>>>                  Run    (std deviation)
>>>>                  BASE                   SPF
>>>> Elapsed Time     1448.65 (5.72312)      1455.84 (4.84951)       0.50%
>>>> User    Time     10135.4 (30.3699)      10148.8 (31.1252)       0.13%
>>>> System  Time     900.47  (2.81131)      923.28  (7.52779)       2.53%
>>>> Percent CPU      761.4   (1.14018)      760.2   (0.447214)      -0.16%
>>>> Context Switches 85380   (3419.52)      84748   (1904.44)       -0.74%
>>>> Sleeps           105064  (1240.96)      105074  (337.612)       0.01%
>>>>
>>>> Average Optimal load -j 16
>>>>                  Run    (std deviation)
>>>>                  BASE                   SPF
>>>> Elapsed Time     920.528 (10.1212)      927.404 (8.91789)       0.75%
>>>> User    Time     11064.8 (981.142)      11085   (990.897)       0.18%
>>>> System  Time     979.904 (84.0615)      1001.14 (82.5523)       2.17%
>>>> Percent CPU      1089.5  (345.894)      1086.1  (343.545)       -0.31%
>>>> Context Switches 159488  (78156.4)      158223  (77472.1)       -0.79%
>>>> Sleeps           110566  (5877.49)      110388  (5617.75)       -0.16%
>>>>
>>>>
>>>> During a run on the SPF, perf events were captured:
>>>>  Performance counter stats for '../kernbench -M':
>>>>          526743764      faults
>>>>                210      spf
>>>>                  3      pagefault:spf_vma_changed
>>>>                  0      pagefault:spf_vma_noanon
>>>>               2278      pagefault:spf_vma_notsup
>>>>                  0      pagefault:spf_vma_access
>>>>                  0      pagefault:spf_pmd_changed
>>>>
>>>> Very few speculative page faults were recorded as most of the processes
>>>> involved are monothreaded (sounds that on this architecture some threads
>>>> were created during the kernel build processing).
>>>>
>>>> Here are the kerbench results on a 80 CPUs Power8 system:
>>>>
>>>> Average Half load -j 40
>>>>                  Run    (std deviation)
>>>>                  BASE                   SPF
>>>> Elapsed Time     117.152 (0.774642)     117.166 (0.476057)      0.01%
>>>> User    Time     4478.52 (24.7688)      4479.76 (9.08555)       0.03%
>>>> System  Time     131.104 (0.720056)     134.04  (0.708414)      2.24%
>>>> Percent CPU      3934    (19.7104)      3937.2  (19.0184)       0.08%
>>>> Context Switches 92125.4 (576.787)      92581.6 (198.622)       0.50%
>>>> Sleeps           317923  (652.499)      318469  (1255.59)       0.17%
>>>>
>>>> Average Optimal load -j 80
>>>>                  Run    (std deviation)
>>>>                  BASE                   SPF
>>>> Elapsed Time     107.73  (0.632416)     107.31  (0.584936)      -0.39%
>>>> User    Time     5869.86 (1466.72)      5871.71 (1467.27)       0.03%
>>>> System  Time     153.728 (23.8573)      157.153 (24.3704)       2.23%
>>>> Percent CPU      5418.6  (1565.17)      5436.7  (1580.91)       0.33%
>>>> Context Switches 223861  (138865)       225032  (139632)        0.52%
>>>> Sleeps           330529  (13495.1)      332001  (14746.2)       0.45%
>>>>
>>>> During a run on the SPF, perf events were captured:
>>>>  Performance counter stats for '../kernbench -M':
>>>>          116730856      faults
>>>>                  0      spf
>>>>                  3      pagefault:spf_vma_changed
>>>>                  0      pagefault:spf_vma_noanon
>>>>                476      pagefault:spf_vma_notsup
>>>>                  0      pagefault:spf_vma_access
>>>>                  0      pagefault:spf_pmd_changed
>>>>
>>>> Most of the processes involved are monothreaded so SPF is not activated but
>>>> there is no impact on the performance.
>>>>
>>>> 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 -mTt <nrcpus>'. To get
>>>> consistent result I repeated the test 100 times and measure the average
>>>> result. The number is the record processes per second, the higher is the
>>>> best.
>>>>
>>>>                 BASE            SPF             delta
>>>> 16 CPUs x86 VM  742.57          1490.24         100.69%
>>>> 80 CPUs P8 node 13105.4         24174.23        84.46%
>>>>
>>>> Here are the performance counter read during a run on a 16 CPUs x86 VM:
>>>>  Performance counter stats for './ebizzy -mTt 16':
>>>>            1706379      faults
>>>>            1674599      spf
>>>>              30588      pagefault:spf_vma_changed
>>>>                  0      pagefault:spf_vma_noanon
>>>>                363      pagefault:spf_vma_notsup
>>>>                  0      pagefault:spf_vma_access
>>>>                  0      pagefault:spf_pmd_changed
>>>>
>>>> And the ones captured during a run on a 80 CPUs Power node:
>>>>  Performance counter stats for './ebizzy -mTt 80':
>>>>            1874773      faults
>>>>            1461153      spf
>>>>             413293      pagefault:spf_vma_changed
>>>>                  0      pagefault:spf_vma_noanon
>>>>                200      pagefault:spf_vma_notsup
>>>>                  0      pagefault:spf_vma_access
>>>>                  0      pagefault:spf_pmd_changed
>>>>
>>>> In ebizzy's case most of the page fault were handled in a speculative way,
>>>> leading the ebizzy performance boost.
>>>>
>>>> ------------------
>>>> Changes since v10 (https://lkml.org/lkml/2018/4/17/572):
>>>>  - Accounted for all review feedbacks from Punit Agrawal, Ganesh Mahendran
>>>>    and Minchan Kim, hopefully.
>>>>  - Remove unneeded check on CONFIG_SPECULATIVE_PAGE_FAULT in
>>>>    __do_page_fault().
>>>>  - Loop in pte_spinlock() and pte_map_lock() when pte try lock fails
>>>>    instead
>>>>    of aborting the speculative page fault handling. Dropping the now
>>>> useless
>>>>    trace event pagefault:spf_pte_lock.
>>>>  - No more try to reuse the fetched VMA during the speculative page fault
>>>>    handling when retrying is needed. This adds a lot of complexity and
>>>>    additional tests done didn't show a significant performance improvement.
>>>>  - Convert IS_ENABLED(CONFIG_NUMA) back to #ifdef due to build error.
>>>>
>>>> [1] http://linux-kernel.2935.n7.nabble.com/RFC-PATCH-0-6-Another-go-at-speculative-page-faults-tt965642.html#none
>>>> [2] https://patchwork.kernel.org/patch/9999687/
>>>>
>>>>
>>>> Laurent Dufour (20):
>>>>   mm: introduce CONFIG_SPECULATIVE_PAGE_FAULT
>>>>   x86/mm: define ARCH_SUPPORTS_SPECULATIVE_PAGE_FAULT
>>>>   powerpc/mm: set ARCH_SUPPORTS_SPECULATIVE_PAGE_FAULT
>>>>   mm: introduce pte_spinlock for FAULT_FLAG_SPECULATIVE
>>>>   mm: make pte_unmap_same compatible with SPF
>>>>   mm: introduce INIT_VMA()
>>>>   mm: protect VMA modifications using VMA sequence count
>>>>   mm: protect mremap() against SPF hanlder
>>>>   mm: protect SPF handler against anon_vma changes
>>>>   mm: cache some VMA fields in the vm_fault structure
>>>>   mm/migrate: Pass vm_fault pointer to migrate_misplaced_page()
>>>>   mm: introduce __lru_cache_add_active_or_unevictable
>>>>   mm: introduce __vm_normal_page()
>>>>   mm: introduce __page_add_new_anon_rmap()
>>>>   mm: protect mm_rb tree with a rwlock
>>>>   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
>>>>   mm: add speculative page fault vmstats
>>>>   powerpc/mm: add speculative page fault
>>>>
>>>> Mahendran Ganesh (2):
>>>>   arm64/mm: define ARCH_SUPPORTS_SPECULATIVE_PAGE_FAULT
>>>>   arm64/mm: add speculative page fault
>>>>
>>>> Peter Zijlstra (4):
>>>>   mm: prepare for FAULT_FLAG_SPECULATIVE
>>>>   mm: VMA sequence count
>>>>   mm: provide speculative fault infrastructure
>>>>   x86/mm: add speculative pagefault handling
>>>>
>>>>  arch/arm64/Kconfig                    |   1 +
>>>>  arch/arm64/mm/fault.c                 |  12 +
>>>>  arch/powerpc/Kconfig                  |   1 +
>>>>  arch/powerpc/mm/fault.c               |  16 +
>>>>  arch/x86/Kconfig                      |   1 +
>>>>  arch/x86/mm/fault.c                   |  27 +-
>>>>  fs/exec.c                             |   2 +-
>>>>  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                    | 136 +++++++-
>>>>  include/linux/mm_types.h              |   7 +
>>>>  include/linux/pagemap.h               |   4 +-
>>>>  include/linux/rmap.h                  |  12 +-
>>>>  include/linux/swap.h                  |  10 +-
>>>>  include/linux/vm_event_item.h         |   3 +
>>>>  include/trace/events/pagefault.h      |  80 +++++
>>>>  include/uapi/linux/perf_event.h       |   1 +
>>>>  kernel/fork.c                         |   5 +-
>>>>  mm/Kconfig                            |  22 ++
>>>>  mm/huge_memory.c                      |   6 +-
>>>>  mm/hugetlb.c                          |   2 +
>>>>  mm/init-mm.c                          |   3 +
>>>>  mm/internal.h                         |  20 ++
>>>>  mm/khugepaged.c                       |   5 +
>>>>  mm/madvise.c                          |   6 +-
>>>>  mm/memory.c                           | 612 +++++++++++++++++++++++++++++-----
>>>>  mm/mempolicy.c                        |  51 ++-
>>>>  mm/migrate.c                          |   6 +-
>>>>  mm/mlock.c                            |  13 +-
>>>>  mm/mmap.c                             | 229 ++++++++++---
>>>>  mm/mprotect.c                         |   4 +-
>>>>  mm/mremap.c                           |  13 +
>>>>  mm/nommu.c                            |   2 +-
>>>>  mm/rmap.c                             |   5 +-
>>>>  mm/swap.c                             |   6 +-
>>>>  mm/swap_state.c                       |   8 +-
>>>>  mm/vmstat.c                           |   5 +-
>>>>  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 +
>>>>  44 files changed, 1161 insertions(+), 211 deletions(-)
>>>>  create mode 100644 include/trace/events/pagefault.h
>>>>
>>>> --
>>>> 2.7.4
>>>>
>>>>
>>>
>>
>