[PATCH v11 00/26] Speculative page faults
Laurent Dufour
ldufour at linux.vnet.ibm.com
Thu Aug 23 00:23:04 AEST 2018
On 03/08/2018 08:36, Song, HaiyanX wrote:
> Hi Laurent,
Hi Haiyan,
Sorry for the late answer, I was off a couple of days.
>
> Thanks for your analysis for the last perf results.
> Your mentioned ," the major differences at the head of the perf report is the 92% testcase which is weirdly not reported
> on the head side", which is a bug of 0-day,and it caused the item is not counted in perf.
>
> I've triggered the test page_fault2 and page_fault3 again only with thread mode of will-it-scale on 0-day (on the same test box,every case tested 3 times).
> I checked the perf report have no above mentioned problem.
>
> I have compared them, found some items have difference, such as below case:
> page_fault2-thp-always: handle_mm_fault, base: 45.22% head: 29.41%
> page_fault3-thp-always: handle_mm_fault, base: 22.95% head: 14.15%
These would mean that the system spends lees time running handle_mm_fault()
when SPF is in the picture in this 2 cases which is good. This should lead to
better results with the SPF series, and I can't find any values higher on the
head side.
>
> So i attached the perf result in mail again, could your have a look again for checking the difference between base and head commit.
I took a close look to all the perf result you sent, but I can't identify any
major difference. But the compiler optimization is getting rid of the
handle_pte_fault() symbol on the base kernel which add complexity to check the
differences.
To get rid of that, I'm proposing that you applied the attached patch to the
spf kernel. This patch is allowing to turn on/off the SPF handler through
/proc/sys/vm/speculative_page_fault.
This should ease the testing by limiting the reboot and avoid kernel's symbols
mismatch. Obviously there is still a small overhead due to the check but it
should not be viewable.
With this patch applied you can simply run
echo 1 > /proc/sys/vm/speculative_page_fault
to run a test with the speculative page fault handler activated. Or run
echo 0 > /proc/sys/vm/speculative_page_fault
to run a test without it.
I'm really sorry to asking that again, but could please run the test
page_fault3_base_THP-Always with and without SPF and capture the perf output.
I think we should focus on that test which showed the biggest regression.
Thanks,
Laurent.
>
> Thanks,
> Haiyan, Song
>
> ________________________________________
> From: owner-linux-mm at kvack.org [owner-linux-mm at kvack.org] on behalf of Laurent Dufour [ldufour at linux.vnet.ibm.com]
> Sent: Tuesday, July 17, 2018 5:36 PM
> To: Song, HaiyanX
> Cc: akpm at linux-foundation.org; mhocko at kernel.org; peterz at infradead.org; kirill at shutemov.name; ak at linux.intel.com; dave at stgolabs.net; jack at suse.cz; Matthew Wilcox; khandual at linux.vnet.ibm.com; aneesh.kumar at linux.vnet.ibm.com; benh at kernel.crashing.org; mpe at ellerman.id.au; paulus at samba.org; Thomas Gleixner; Ingo Molnar; hpa at zytor.com; Will Deacon; Sergey Senozhatsky; sergey.senozhatsky.work at 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 at vger.kernel.org; linux-mm at kvack.org; haren at linux.vnet.ibm.com; npiggin at gmail.com; bsingharora at gmail.com; paulmck at linux.vnet.ibm.com; Tim Chen; linuxppc-dev at lists.ozlabs.org; x86 at kernel.org
> Subject: Re: [PATCH v11 00/26] Speculative page faults
>
> On 13/07/2018 05:56, Song, HaiyanX wrote:
>> Hi Laurent,
>
> Hi Haiyan,
>
> Thanks a lot for sharing this perf reports.
>
> I looked at them closely, and I've to admit that I was not able to found a
> major difference between the base and the head report, except that
> handle_pte_fault() is no more in-lined in the head one.
>
> As expected, __handle_speculative_fault() is never traced since these tests are
> dealing with file mapping, not handled in the speculative way.
>
> When running these test did you seen a major differences in the test's result
> between base and head ?
>
> From the number of cycles counted, the biggest difference is page_fault3 when
> run with the THP enabled:
> BASE HEAD Delta
> page_fault2_base_thp_never 1142252426747 1065866197589 -6.69%
> page_fault2_base_THP-Alwasys 1124844374523 1076312228927 -4.31%
> page_fault3_base_thp_never 1099387298152 1134118402345 3.16%
> page_fault3_base_THP-Always 1059370178101 853985561949 -19.39%
>
>
> The very weird thing is the difference of the delta cycles reported between
> thp never and thp always, because the speculative way is aborted when checking
> for the vma->ops field, which is the same in both case, and the thp is never
> checked. So there is no code covering differnce, on the speculative path,
> between these 2 cases. This leads me to think that there are other interactions
> interfering in the measure.
>
> Looking at the perf-profile_page_fault3_*_THP-Always, the major differences at
> the head of the perf report is the 92% testcase which is weirdly not reported
> on the head side :
> 92.02% 22.33% page_fault3_processes [.] testcase
> 92.02% testcase
>
> Then the base reported 37.67% for __do_page_fault() where the head reported
> 48.41%, but the only difference in this function, between base and head, is the
> call to handle_speculative_fault(). But this is a macro checking for the fault
> flags, and mm->users and then calling __handle_speculative_fault() if needed.
> So this can't explain this difference, except if __handle_speculative_fault()
> is inlined in __do_page_fault().
> Is this the case on your build ?
>
> Haiyan, do you still have the output of the test to check those numbers too ?
>
> Cheers,
> Laurent
>
>> I attached the perf-profile.gz file for case page_fault2 and page_fault3. These files were captured during test the related test case.
>> Please help to check on these data if it can help you to find the higher change. Thanks.
>>
>> File name perf-profile_page_fault2_head_THP-Always.gz, means the perf-profile result get from page_fault2
>> tested for head commit (a7a8993bfe3ccb54ad468b9f1799649e4ad1ff12) with THP_always configuration.
>>
>> Best regards,
>> Haiyan Song
>>
>> ________________________________________
>> From: owner-linux-mm at kvack.org [owner-linux-mm at kvack.org] on behalf of Laurent Dufour [ldufour at linux.vnet.ibm.com]
>> Sent: Thursday, July 12, 2018 1:05 AM
>> To: Song, HaiyanX
>> Cc: akpm at linux-foundation.org; mhocko at kernel.org; peterz at infradead.org; kirill at shutemov.name; ak at linux.intel.com; dave at stgolabs.net; jack at suse.cz; Matthew Wilcox; khandual at linux.vnet.ibm.com; aneesh.kumar at linux.vnet.ibm.com; benh at kernel.crashing.org; mpe at ellerman.id.au; paulus at samba.org; Thomas Gleixner; Ingo Molnar; hpa at zytor.com; Will Deacon; Sergey Senozhatsky; sergey.senozhatsky.work at 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 at vger.kernel.org; linux-mm at kvack.org; haren at linux.vnet.ibm.com; npiggin at gmail.com; bsingharora at gmail.com; paulmck at linux.vnet.ibm.com; Tim Chen; linuxppc-dev at lists.ozlabs.org; x86 at kernel.org
>> Subject: Re: [PATCH v11 00/26] Speculative page faults
>>
>> Hi Haiyan,
>>
>> Do you get a chance to capture some performance cycles on your system ?
>> I still can't get these numbers on my hardware.
>>
>> Thanks,
>> Laurent.
>>
>> On 04/07/2018 09:51, Laurent Dufour wrote:
>>> On 04/07/2018 05:23, Song, HaiyanX wrote:
>>>> Hi Laurent,
>>>>
>>>>
>>>> For the test result on Intel 4s skylake platform (192 CPUs, 768G Memory), the below test cases all were run 3 times.
>>>> I check the test results, only page_fault3_thread/enable THP have 6% stddev for head commit, other tests have lower stddev.
>>>
>>> Repeating the test only 3 times seems a bit too low to me.
>>>
>>> I'll focus on the higher change for the moment, but I don't have access to such
>>> a hardware.
>>>
>>> Is possible to provide a diff between base and SPF of the performance cycles
>>> measured when running page_fault3 and page_fault2 when the 20% change is detected.
>>>
>>> Please stay focus on the test case process to see exactly where the series is
>>> impacting.
>>>
>>> Thanks,
>>> Laurent.
>>>
>>>>
>>>> And I did not find other high variation on test case result.
>>>>
>>>> a). Enable THP
>>>> testcase base stddev change head stddev metric
>>>> page_fault3/enable THP 10519 ± 3% -20.5% 8368 ±6% will-it-scale.per_thread_ops
>>>> page_fault2/enalbe THP 8281 ± 2% -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
>>>>
>>>>
>>>> Best regards,
>>>> Haiyan Song
>>>> ________________________________________
>>>> From: Laurent Dufour [ldufour at linux.vnet.ibm.com]
>>>> Sent: Monday, July 02, 2018 4:59 PM
>>>> To: Song, HaiyanX
>>>> Cc: akpm at linux-foundation.org; mhocko at kernel.org; peterz at infradead.org; kirill at shutemov.name; ak at linux.intel.com; dave at stgolabs.net; jack at suse.cz; Matthew Wilcox; khandual at linux.vnet.ibm.com; aneesh.kumar at linux.vnet.ibm.com; benh at kernel.crashing.org; mpe at ellerman.id.au; paulus at samba.org; Thomas Gleixner; Ingo Molnar; hpa at zytor.com; Will Deacon; Sergey Senozhatsky; sergey.senozhatsky.work at 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 at vger.kernel.org; linux-mm at kvack.org; haren at linux.vnet.ibm.com; npiggin at gmail.com; bsingharora at gmail.com; paulmck at linux.vnet.ibm.com; Tim Chen; linuxppc-dev at lists.ozlabs.org; x86 at kernel.org
>>>> Subject: Re: [PATCH v11 00/26] Speculative page faults
>>>>
>>>> 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 at kvack.org [owner-linux-mm at kvack.org] on behalf of Laurent Dufour [ldufour at linux.vnet.ibm.com]
>>>>> Sent: Monday, May 28, 2018 4:54 PM
>>>>> To: Song, HaiyanX
>>>>> Cc: akpm at linux-foundation.org; mhocko at kernel.org; peterz at infradead.org; kirill at shutemov.name; ak at linux.intel.com; dave at stgolabs.net; jack at suse.cz; Matthew Wilcox; khandual at linux.vnet.ibm.com; aneesh.kumar at linux.vnet.ibm.com; benh at kernel.crashing.org; mpe at ellerman.id.au; paulus at samba.org; Thomas Gleixner; Ingo Molnar; hpa at zytor.com; Will Deacon; Sergey Senozhatsky; sergey.senozhatsky.work at 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 at vger.kernel.org; linux-mm at kvack.org; haren at linux.vnet.ibm.com; npiggin at gmail.com; bsingharora at gmail.com; paulmck at linux.vnet.ibm.com; Tim Chen; linuxppc-dev at lists.ozlabs.org; x86 at 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 at kvack.org [owner-linux-mm at kvack.org] on behalf of Laurent Dufour [ldufour at linux.vnet.ibm.com]
>>>>>>>> Sent: Thursday, May 17, 2018 7:06 PM
>>>>>>>> To: akpm at linux-foundation.org; mhocko at kernel.org; peterz at infradead.org; kirill at shutemov.name; ak at linux.intel.com; dave at stgolabs.net; jack at suse.cz; Matthew Wilcox; khandual at linux.vnet.ibm.com; aneesh.kumar at linux.vnet.ibm.com; benh at kernel.crashing.org; mpe at ellerman.id.au; paulus at samba.org; Thomas Gleixner; Ingo Molnar; hpa at zytor.com; Will Deacon; Sergey Senozhatsky; sergey.senozhatsky.work at 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 at vger.kernel.org; linux-mm at kvack.org; haren at linux.vnet.ibm.com; npiggin at gmail.com; bsingharora at gmail.com; paulmck at linux.vnet.ibm.com; Tim Chen; linuxppc-dev at lists.ozlabs.org; x86 at 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
>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>>
>>>>>
>>>>
>>>>
>>>
>>
>
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