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[148.163.156.1]) by mx.google.com with ESMTPS id u51si27256edm.51.2019.04.16.06.46.47 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 16 Apr 2019 06:46:47 -0700 (PDT) Received-SPF: pass (google.com: domain of ldufour@linux.ibm.com designates 148.163.156.1 as permitted sender) client-ip=148.163.156.1; Authentication-Results: mx.google.com; spf=pass (google.com: domain of ldufour@linux.ibm.com designates 148.163.156.1 as permitted sender) smtp.mailfrom=ldufour@linux.ibm.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=ibm.com Received: from pps.filterd (m0098394.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.27/8.16.0.27) with SMTP id x3GDkLQ2129886 for ; Tue, 16 Apr 2019 09:46:45 -0400 Received: from e06smtp03.uk.ibm.com (e06smtp03.uk.ibm.com [195.75.94.99]) by mx0a-001b2d01.pphosted.com with ESMTP id 2rwe6cnnfa-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Tue, 16 Apr 2019 09:46:36 -0400 Received: from localhost by e06smtp03.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! 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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Tue, 16 Apr 2019 14:45:27 +0100 Received: from d06av22.portsmouth.uk.ibm.com (d06av22.portsmouth.uk.ibm.com [9.149.105.58]) by b06cxnps3074.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x3GDjPGb56099060 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 16 Apr 2019 13:45:25 GMT Received: from d06av22.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 3386F4C046; Tue, 16 Apr 2019 13:45:25 +0000 (GMT) Received: from d06av22.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 25CF34C050; Tue, 16 Apr 2019 13:45:23 +0000 (GMT) Received: from nimbus.lab.toulouse-stg.fr.ibm.com (unknown [9.101.4.33]) by d06av22.portsmouth.uk.ibm.com (Postfix) with ESMTP; Tue, 16 Apr 2019 13:45:23 +0000 (GMT) From: Laurent Dufour 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 , aneesh.kumar@linux.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 , kemi.wang@intel.com, Daniel Jordan , David Rientjes , Jerome Glisse , Ganesh Mahendran , Minchan Kim , Punit Agrawal , vinayak menon , Yang Shi , zhong jiang , Haiyan Song , Balbir Singh , sj38.park@gmail.com, Michel Lespinasse , Mike Rapoport Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, haren@linux.vnet.ibm.com, npiggin@gmail.com, paulmck@linux.vnet.ibm.com, Tim Chen , linuxppc-dev@lists.ozlabs.org, x86@kernel.org Subject: [PATCH v12 00/31] Speculative page faults Date: Tue, 16 Apr 2019 15:44:51 +0200 X-Mailer: git-send-email 2.21.0 MIME-Version: 1.0 X-TM-AS-GCONF: 00 x-cbid: 19041613-0012-0000-0000-0000030F6EEC X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19041613-0013-0000-0000-00002147A847 Message-Id: <20190416134522.17540-1-ldufour@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-04-16_05:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1904160093 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: X-Virus-Scanned: ClamAV using ClamSMTP This is a port on kernel 5.1 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 of page fault is named speculative page fault. If the speculative page fault fails because a concurrency has been detected or because underlying PMD or PTE tables are not yet allocating, it is failing its processing and a regular 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 protecting the MM RB tree with RCU and by using a reference counter on each VMA. When fetching a VMA under the RCU protection, the VMA's reference counter is incremented to ensure that the VMA will not freed in our back during the SPF processing. Once that processing is done the VMA's reference counter is decremented. To ensure that a VMA is still present when walking the RB tree locklessly, the VMA's reference counter is incremented when that VMA is linked in the RB tree. When the VMA is unlinked from the RB tree, its reference counter will be decremented at the end of the RCU grace period, ensuring it will be available during this time. This means that the VMA freeing could be delayed and could delay the file closing for file mapping. Since the SPF handler is not able to manage file mapping, file is closed synchronously and not during the RCU cleaning. This is safe since the page fault handler is aborting if a file pointer is associated to the VMA. Using RCU fixes the overhead seen by Haiyan Song using the will-it-scale benchmark [2]. 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 = find_vma_rcu() 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 ... put_vma(vma) } 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:*' 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 It is possible to deactivate the speculative page fault handler by echoing 0 in /proc/sys/vm/speculative_page_fault. This series builds on top of v5.1-rc4-mmotm-2019-04-09-17-51 and is functional on x86, PowerPC. I cross built it on arm64 but I was not able to test it. This series is also available on github [4]. --------------------- Real Workload results Test using a "popular in memory multithreaded database product" on 128cores SMT8 Power system are in progress and I will come back with performance mesurement as soon as possible. With the previous series we seen up to 30% improvements in the number of transaction processed per second, and we hope this will be the case with this series too. ------------------ Benchmarks results Base kernel is v5.1-rc4-mmotm-2019-04-09-17-51 SPF is BASE + this series Kernbench: ---------- Here are the results on a 48 CPUs X86 system using kernbench on a 5.0 kernel (kernel is build 5 times): Average Half load -j 24 Run (std deviation) BASE SPF Elapsed Time 56.52 (1.39185) 56.256 (1.15106) 0.47% User Time 980.018 (2.94734) 984.958 (1.98518) -0.50% System Time 130.744 (1.19148) 133.616 (0.873573) -2.20% Percent CPU 1965.6 (49.682) 1988.4 (40.035) -1.16% Context Switches 29926.6 (272.789) 30472.4 (109.569) -1.82% Sleeps 124793 (415.87) 125003 (591.008) -0.17% Average Optimal load -j 48 Run (std deviation) BASE SPF Elapsed Time 46.354 (0.917949) 45.968 (1.42786) 0.83% User Time 1193.42 (224.96) 1196.78 (223.28) -0.28% System Time 143.306 (13.2726) 146.177 (13.2659) -2.00% Percent CPU 2668.6 (743.157) 2699.9 (753.767) -1.17% Context Switches 62268.3 (34097.1) 62721.7 (33999.1) -0.73% Sleeps 132556 (8222.99) 132607 (8077.6) -0.04% During a run on the SPF, perf events were captured: Performance counter stats for '../kernbench -M': 525,873,132 faults 242 spf 0 pagefault:spf_vma_changed 0 pagefault:spf_vma_noanon 441 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 1024 CPUs Power8 VM: 5.1.0-rc4-mm1+ 5.1.0-rc4-mm1-spf-rcu+ Average Half load -j 512 Run (std deviation): Elapsed Time 52.52 (0.906697) 52.778 (0.510069) -0.49% User Time 3855.43 (76.378) 3890.44 (73.0466) -0.91% System Time 1977.24 (182.316) 1974.56 (166.097) 0.14% Percent CPU 11111.6 (540.461) 11115.2 (458.907) -0.03% Context Switches 83245.6 (3061.44) 83651.8 (1202.31) -0.49% Sleeps 613459 (23091.8) 628378 (27485.2) -2.43% Average Optimal load -j 1024 Run (std deviation): Elapsed Time 52.964 (0.572346) 53.132 (0.825694) -0.32% User Time 4058.22 (222.034) 4070.2 (201.646) -0.30% System Time 2672.81 (759.207) 2712.13 (797.292) -1.47% Percent CPU 12756.7 (1786.35) 12806.5 (1858.89) -0.39% Context Switches 88818.5 (6772) 87890.6 (5567.72) 1.04% Sleeps 618658 (20842.2) 636297 (25044) -2.85% During a run on the SPF, perf events were captured: Performance counter stats for '../kernbench -M': 149 375 832 faults 1 spf 0 pagefault:spf_vma_changed 0 pagefault:spf_vma_noanon 561 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 '. 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 24 CPUs x86 5492.69 9383.07 70.83% 1024 CPUS P8 VM 8476.74 17144.38 102% Here are the performance counter read during a run on a 48 CPUs x86 node: Performance counter stats for './ebizzy -mTt 48': 11,846,569 faults 10,886,706 spf 957,702 pagefault:spf_vma_changed 0 pagefault:spf_vma_noanon 815 pagefault:spf_vma_notsup 0 pagefault:spf_vma_access 0 pagefault:spf_pmd_changed And the ones captured during a run on a 1024 CPUs Power VM: Performance counter stats for './ebizzy -mTt 1024': 1 359 789 faults 1 284 910 spf 72 085 pagefault:spf_vma_changed 0 pagefault:spf_vma_noanon 2 669 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 v11 [3] - Check vm_ops.fault instead of vm_ops since now all the VMA as a vm_ops. - Abort speculative page fault when doing swap readhead because VMA's boundaries are not protected at this time. Doing this the first swap in is doing a readhead, the next fault should be handled in a speculative way as the page is present in the swap read page. - Handle a race between copy_pte_range() and the wp_page_copy called by the speculative page fault handler. - Ported to Kernel v5.0 - Moved VM_FAULT_PTNOTSAME define in mm_types.h - Use RCU to protect the MM RB tree instead of a rwlock. - Add a toggle interface: /proc/sys/vm/speculative_page_fault [1] https://lore.kernel.org/linux-mm/20141020215633.717315139@infradead.org/ [2] https://lore.kernel.org/linux-mm/9FE19350E8A7EE45B64D8D63D368C8966B847F54@SHSMSX101.ccr.corp.intel.com/ [3] https://lore.kernel.org/linux-mm/1526555193-7242-1-git-send-email-ldufour@linux.vnet.ibm.com/ [4] https://github.com/ldu4/linux/tree/spf-v12 Laurent Dufour (25): 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 against PTE changes done by dup_mmap() mm: protect the RB tree with a sequence lock mm: introduce vma reference counter mm: Introduce find_vma_rcu() mm: don't do swap readahead during speculative page fault 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 mm: Add a speculative page fault switch in sysctl 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 | 14 + fs/exec.c | 1 + 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 | 138 +++++- include/linux/mm_types.h | 16 +- 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 | 35 +- kernel/sysctl.c | 9 + mm/Kconfig | 22 + mm/huge_memory.c | 6 +- mm/hugetlb.c | 2 + mm/init-mm.c | 3 + mm/internal.h | 45 ++ mm/khugepaged.c | 5 + mm/madvise.c | 6 +- mm/memory.c | 631 ++++++++++++++++++++++---- mm/mempolicy.c | 51 ++- mm/migrate.c | 6 +- mm/mlock.c | 13 +- mm/mmap.c | 249 ++++++++-- mm/mprotect.c | 4 +- mm/mremap.c | 13 + mm/nommu.c | 1 + mm/rmap.c | 5 +- mm/swap.c | 6 +- mm/swap_state.c | 10 +- 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 + 45 files changed, 1277 insertions(+), 196 deletions(-) create mode 100644 include/trace/events/pagefault.h Reviewed-by: Michel Lespinasse