- 06 Apr, 2023 40 commits
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Raghavendra K T authored
During Numa scanning make sure only relevant vmas of the tasks are scanned. Before: All the tasks of a process participate in scanning the vma even if they do not access vma in it's lifespan. Now: Except cases of first few unconditional scans, if a process do not touch vma (exluding false positive cases of PID collisions) tasks no longer scan all vma Logic used: 1) 6 bits of PID used to mark active bit in vma numab status during fault to remember PIDs accessing vma. (Thanks Mel) 2) Subsequently in scan path, vma scanning is skipped if current PID had not accessed vma. 3) First two times we do allow unconditional scan to preserve earlier behaviour of scanning. Acknowledgement to Bharata B Rao <bharata@amd.com> for initial patch to store pid information and Peter Zijlstra <peterz@infradead.org> (Usage of test and set bit) Link: https://lkml.kernel.org/r/092f03105c7c1d3450f4636b1ea350407f07640e.1677672277.git.raghavendra.kt@amd.comSigned-off-by:
Raghavendra K T <raghavendra.kt@amd.com> Suggested-by:
Mel Gorman <mgorman@techsingularity.net> Cc: David Hildenbrand <david@redhat.com> Cc: Disha Talreja <dishaa.talreja@amd.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: Mike Rapoport <rppt@kernel.org> Signed-off-by:
Andrew Morton <akpm@linux-foundation.org>
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Mel Gorman authored
Pach series "sched/numa: Enhance vma scanning", v3. The patchset proposes one of the enhancements to numa vma scanning suggested by Mel. This is continuation of [3]. Reposting the rebased patchset to akpm mm-unstable tree (March 1) Existing mechanism of scan period involves, scan period derived from per-thread stats. Process Adaptive autoNUMA [1] proposed to gather NUMA fault stats at per-process level to capture aplication behaviour better. During that course of discussion, Mel proposed several ideas to enhance current numa balancing. One of the suggestion was below Track what threads access a VMA. The suggestion was to use an unsigned long pid_mask and use the lower bits to tag approximately what threads access a VMA. Skip VMAs that did not trap a fault. This would be approximate because of PID collisions but would reduce scanning of areas the thread is not interested in. The above suggestion intends not to penalize threads that has no interest in the vma, thus reduce scanning overhead. V3 changes are mostly based on PeterZ comments (details below in changes) Summary of patchset: Current patchset implements: 1. Delay the vma scanning logic for newly created VMA's so that additional overhead of scanning is not incurred for short lived tasks (implementation by Mel) 2. Store the information of tasks accessing VMA in 2 windows. It is regularly cleared in (4*sysctl_numa_balancing_scan_delay) interval. The above time is derived from experimenting (Suggested by PeterZ) to balance between frequent clearing vs obsolete access data 3. hash_32 used to encode task index accessing VMA information 4. VMA's acess information is used to skip scanning for the tasks which had not accessed VMA Changes since V2: patch1: - Renaming of structure, macro to function, - Add explanation to heuristics - Adding more details from result (PeterZ) Patch2: - Usage of test and set bit (PeterZ) - Move storing access PID info to numa_migrate_prep() - Add a note on fainess among tasks allowed to scan (PeterZ) Patch3: - Maintain two windows of access PID information (PeterZ supported implementation and Gave idea to extend to N if needed) Patch4: - Apply hash_32 function to track VMA accessing PIDs (PeterZ) Changes since RFC V1: - Include Mel's vma scan delay patch - Change the accessing pid store logic (Thanks Mel) - Fencing structure / code to NUMA_BALANCING (David, Mel) - Adding clearing access PID logic (Mel) - Descriptive change log ( Mike Rapoport) Things to ponder over: ========================================== - Improvement to clearing accessing PIDs logic (discussed in-detail in patch3 itself (Done in this patchset by implementing 2 window history) - Current scan period is not changed in the patchset, so we do see frequent tries to scan. Relaxing scan period dynamically could improve results further. [1] sched/numa: Process Adaptive autoNUMA Link: https://lore.kernel.org/lkml/20220128052851.17162-1-bharata@amd.com/T/ [2] RFC V1 Link: https://lore.kernel.org/all/cover.1673610485.git.raghavendra.kt@amd.com/ [3] V2 Link: https://lore.kernel.org/lkml/cover.1675159422.git.raghavendra.kt@amd.com/ Results: Summary: Huge autonuma cost reduction seen in mmtest. Kernbench improvement is more than 5% and huge system time (80%+) improvement from mmtest autonuma. (dbench had huge std deviation to post) kernbench =========== 6.2.0-mmunstable-base 6.2.0-mmunstable-patched Amean user-256 22002.51 ( 0.00%) 22649.95 * -2.94%* Amean syst-256 10162.78 ( 0.00%) 8214.13 * 19.17%* Amean elsp-256 160.74 ( 0.00%) 156.92 * 2.38%* Duration User 66017.43 67959.84 Duration System 30503.15 24657.03 Duration Elapsed 504.61 493.12 6.2.0-mmunstable-base 6.2.0-mmunstable-patched Ops NUMA alloc hit 1738835089.00 1738780310.00 Ops NUMA alloc local 1738834448.00 1738779711.00 Ops NUMA base-page range updates 477310.00 392566.00 Ops NUMA PTE updates 477310.00 392566.00 Ops NUMA hint faults 96817.00 87555.00 Ops NUMA hint local faults % 10150.00 2192.00 Ops NUMA hint local percent 10.48 2.50 Ops NUMA pages migrated 86660.00 85363.00 Ops AutoNUMA cost 489.07 442.14 autonumabench =============== 6.2.0-mmunstable-base 6.2.0-mmunstable-patched Amean syst-NUMA01 399.50 ( 0.00%) 52.05 * 86.97%* Amean syst-NUMA01_THREADLOCAL 0.21 ( 0.00%) 0.22 * -5.41%* Amean syst-NUMA02 0.80 ( 0.00%) 0.78 * 2.68%* Amean syst-NUMA02_SMT 0.65 ( 0.00%) 0.68 * -3.95%* Amean elsp-NUMA01 313.26 ( 0.00%) 313.11 * 0.05%* Amean elsp-NUMA01_THREADLOCAL 1.06 ( 0.00%) 1.08 * -1.76%* Amean elsp-NUMA02 3.19 ( 0.00%) 3.24 * -1.52%* Amean elsp-NUMA02_SMT 3.72 ( 0.00%) 3.61 * 2.92%* Duration User 396433.47 324835.96 Duration System 2808.70 376.66 Duration Elapsed 2258.61 2258.12 6.2.0-mmunstable-base 6.2.0-mmunstable-patched Ops NUMA alloc hit 59921806.00 49623489.00 Ops NUMA alloc miss 0.00 0.00 Ops NUMA interleave hit 0.00 0.00 Ops NUMA alloc local 59920880.00 49622594.00 Ops NUMA base-page range updates 152259275.00 50075.00 Ops NUMA PTE updates 152259275.00 50075.00 Ops NUMA PMD updates 0.00 0.00 Ops NUMA hint faults 154660352.00 39014.00 Ops NUMA hint local faults % 138550501.00 23139.00 Ops NUMA hint local percent 89.58 59.31 Ops NUMA pages migrated 8179067.00 14147.00 Ops AutoNUMA cost 774522.98 195.69 This patch (of 4): Currently whenever a new task is created we wait for sysctl_numa_balancing_scan_delay to avoid unnessary scanning overhead. Extend the same logic to new or very short-lived VMAs. [raghavendra.kt@amd.com: add initialization in vm_area_dup())] Link: https://lkml.kernel.org/r/cover.1677672277.git.raghavendra.kt@amd.com Link: https://lkml.kernel.org/r/7a6fbba87c8b51e67efd3e74285bb4cb311a16ca.1677672277.git.raghavendra.kt@amd.comSigned-off-by:
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Heiko Carstens authored
Attempt VMA lock-based page fault handling first, and fall back to the existing mmap_lock-based handling if that fails. This is the s390 variant of "x86/mm: try VMA lock-based page fault handling first". Link: https://lkml.kernel.org/r/20230314132808.1266335-1-hca@linux.ibm.comSigned-off-by:
Heiko Carstens <hca@linux.ibm.com> Cc: Alexander Gordeev <agordeev@linux.ibm.com> Cc: Christian Borntraeger <borntraeger@linux.ibm.com> Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com> Cc: Suren Baghdasaryan <surenb@google.com> Cc: Sven Schnelle <svens@linux.ibm.com> Cc: Vasily Gorbik <gor@linux.ibm.com> Signed-off-by:
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Suren Baghdasaryan authored
vma->lock being part of the vm_area_struct causes performance regression during page faults because during contention its count and owner fields are constantly updated and having other parts of vm_area_struct used during page fault handling next to them causes constant cache line bouncing. Fix that by moving the lock outside of the vm_area_struct. All attempts to keep vma->lock inside vm_area_struct in a separate cache line still produce performance regression especially on NUMA machines. Smallest regression was achieved when lock is placed in the fourth cache line but that bloats vm_area_struct to 256 bytes. Considering performance and memory impact, separate lock looks like the best option. It increases memory footprint of each VMA but that can be optimized later if the new size causes issues. Note that after this change vma_init() does not allocate or initialize vma->lock anymore. A number of drivers allocate a pseudo VMA on the stack but they never use the VMA's lock, therefore it does not need to be allocated. The future drivers which might need the VMA lock should use vm_area_alloc()/vm_area_free() to allocate the VMA. Link: https://lkml.kernel.org/r/20230227173632.3292573-34-surenb@google.comSigned-off-by:
Suren Baghdasaryan <surenb@google.com> Signed-off-by:
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Suren Baghdasaryan authored
call_rcu() can take a long time when callback offloading is enabled. Its use in the vm_area_free can cause regressions in the exit path when multiple VMAs are being freed. Because exit_mmap() is called only after the last mm user drops its refcount, the page fault handlers can't be racing with it. Any other possible user like oom-reaper or process_mrelease are already synchronized using mmap_lock. Therefore exit_mmap() can free VMAs directly, without the use of call_rcu(). Expose __vm_area_free() and use it from exit_mmap() to avoid possible call_rcu() floods and performance regressions caused by it. Link: https://lkml.kernel.org/r/20230227173632.3292573-33-surenb@google.comSigned-off-by:
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Laurent Dufour authored
Attempt VMA lock-based page fault handling first, and fall back to the existing mmap_lock-based handling if that fails. Copied from "x86/mm: try VMA lock-based page fault handling first" [ldufour@linux.ibm.com: powerpc/mm: fix mmap_lock bad unlock] Link: https://lkml.kernel.org/r/20230306154244.17560-1-ldufour@linux.ibm.com Link: https://lore.kernel.org/linux-mm/842502FB-F99C-417C-9648-A37D0ECDC9CE@linux.ibm.com Link: https://lkml.kernel.org/r/20230227173632.3292573-32-surenb@google.comSigned-off-by:
Laurent Dufour <ldufour@linux.ibm.com> Signed-off-by:
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Suren Baghdasaryan authored
Attempt VMA lock-based page fault handling first, and fall back to the existing mmap_lock-based handling if that fails. Link: https://lkml.kernel.org/r/20230227173632.3292573-31-surenb@google.comSigned-off-by:
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Suren Baghdasaryan authored
Attempt VMA lock-based page fault handling first, and fall back to the existing mmap_lock-based handling if that fails. Link: https://lkml.kernel.org/r/20230227173632.3292573-30-surenb@google.comSigned-off-by:
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Suren Baghdasaryan authored
Add a new CONFIG_PER_VMA_LOCK_STATS config option to dump extra statistics about handling page fault under VMA lock. Link: https://lkml.kernel.org/r/20230227173632.3292573-29-surenb@google.comSigned-off-by:
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Suren Baghdasaryan authored
Due to the possibility of handle_userfault dropping mmap_lock, avoid fault handling under VMA lock and retry holding mmap_lock. This can be handled more gracefully in the future. Link: https://lkml.kernel.org/r/20230227173632.3292573-28-surenb@google.comSigned-off-by:
Peter Xu <peterx@redhat.com> Signed-off-by:
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Suren Baghdasaryan authored
Due to the possibility of do_swap_page dropping mmap_lock, abort fault handling under VMA lock and retry holding mmap_lock. This can be handled more gracefully in the future. Link: https://lkml.kernel.org/r/20230227173632.3292573-27-surenb@google.comSigned-off-by:
Laurent Dufour <laurent.dufour@fr.ibm.com> Signed-off-by:
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Suren Baghdasaryan authored
Add a new flag to distinguish page faults handled under protection of per-vma lock. [surenb@google.com: document FAULT_FLAG_VMA_LOCK flag] Link: https://lkml.kernel.org/r/20230301022720.1380780-2-surenb@google.com Link: https://lore.kernel.org/all/20230301113648.7c279865@canb.auug.org.au/ Link: https://lkml.kernel.org/r/20230227173632.3292573-26-surenb@google.comSigned-off-by:
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Suren Baghdasaryan authored
When vma->anon_vma is not set, page fault handler will set it by either reusing anon_vma of an adjacent VMA if VMAs are compatible or by allocating a new one. find_mergeable_anon_vma() walks VMA tree to find a compatible adjacent VMA and that requires not only the faulting VMA to be stable but also the tree structure and other VMAs inside that tree. Therefore locking just the faulting VMA is not enough for this search. Fall back to taking mmap_lock when vma->anon_vma is not set. This situation happens only on the first page fault and should not affect overall performance. Link: https://lkml.kernel.org/r/20230227173632.3292573-25-surenb@google.comSigned-off-by:
Hyeonggon Yoo <42.hyeyoo@gmail.com> Signed-off-by:
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Suren Baghdasaryan authored
Introduce lock_vma_under_rcu function to lookup and lock a VMA during page fault handling. When VMA is not found, can't be locked or changes after being locked, the function returns NULL. The lookup is performed under RCU protection to prevent the found VMA from being destroyed before the VMA lock is acquired. VMA lock statistics are updated according to the results. For now only anonymous VMAs can be searched this way. In other cases the function returns NULL. Link: https://lkml.kernel.org/r/20230227173632.3292573-24-surenb@google.comSigned-off-by:
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Suren Baghdasaryan authored
Per-vma locking mechanism will search for VMA under RCU protection and then after locking it, has to ensure it was not removed from the VMA tree after we found it. To make this check efficient, introduce a vma->detached flag to mark VMAs which were removed from the VMA tree. Link: https://lkml.kernel.org/r/20230227173632.3292573-23-surenb@google.comSigned-off-by:
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Suren Baghdasaryan authored
Page fault handlers might need to fire MMU notifications while a new notifier is being registered. Modify mm_take_all_locks to write-lock all VMAs and prevent this race with page fault handlers that would hold VMA locks. VMAs are locked before i_mmap_rwsem and anon_vma to keep the same locking order as in page fault handlers. Link: https://lkml.kernel.org/r/20230227173632.3292573-22-surenb@google.comSigned-off-by:
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Suren Baghdasaryan authored
Assert there are no holders of VMA lock for reading when it is about to be destroyed. Link: https://lkml.kernel.org/r/20230227173632.3292573-21-surenb@google.comSigned-off-by:
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Suren Baghdasaryan authored
Normally free_pgtables needs to lock affected VMAs except for the case when VMAs were isolated under VMA write-lock. munmap() does just that, isolating while holding appropriate locks and then downgrading mmap_lock and dropping per-VMA locks before freeing page tables. Add a parameter to free_pgtables for such scenario. Link: https://lkml.kernel.org/r/20230227173632.3292573-20-surenb@google.comSigned-off-by:
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Suren Baghdasaryan authored
Write-locking VMAs before isolating them ensures that page fault handlers don't operate on isolated VMAs. [surenb@google.com: mm/nommu: remove unnecessary VMA locking] Link: https://lkml.kernel.org/r/20230301190457.1498985-1-surenb@google.com Link: https://lore.kernel.org/all/Y%2F8CJQGNuMUTdLwP@localhost/ Link: https://lkml.kernel.org/r/20230227173632.3292573-19-surenb@google.comSigned-off-by:
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Suren Baghdasaryan authored
Write-lock VMA as locked before copying it and when copy_vma produces a new VMA. Link: https://lkml.kernel.org/r/20230227173632.3292573-18-surenb@google.comSigned-off-by:
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Suren Baghdasaryan authored
Write-lock all VMAs which might be affected by a merge, split, expand or shrink operations. All these operations use vma_prepare() before making the modifications, therefore it provides a centralized place to perform VMA locking. [surenb@google.com: remove unnecessary vp->vma check in vma_prepare] Link: https://lkml.kernel.org/r/20230301022720.1380780-1-surenb@google.com Link: https://lore.kernel.org/r/202302281802.J93Nma7q-lkp@intel.com/ Link: https://lkml.kernel.org/r/20230227173632.3292573-17-surenb@google.comSigned-off-by:
David Hildenbrand <david@redhat.com> Reviewed-by:
Liam R. Howlett <Liam.Howlett@oracle.com> Cc: David Howells <dhowells@redhat.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Laurent Dufour <laurent.dufour@fr.ibm.com> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Pavel Tatashin <pasha.tatashin@soleen.com> Cc: Stephen Rothwell <sfr@canb.auug.org.au> Cc: Yu Zhao <yuzhao@google.com> Signed-off-by:
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Suren Baghdasaryan authored
Protect VMA from concurrent page fault handler while collapsing a huge page. Page fault handler needs a stable PMD to use PTL and relies on per-VMA lock to prevent concurrent PMD changes. pmdp_collapse_flush(), set_huge_pmd() and collapse_and_free_pmd() can modify a PMD, which will not be detected by a page fault handler without proper locking. Before this patch, page tables can be walked under any one of the mmap_lock, the mapping lock, and the anon_vma lock; so when khugepaged unlinks and frees page tables, it must ensure that all of those either are locked or don't exist. This patch adds a fourth lock under which page tables can be traversed, and so khugepaged must also lock out that one. [surenb@google.com: vm_lock/i_mmap_rwsem inversion in retract_page_tables] Link: https://lkml.kernel.org/r/20230303213250.3555716-1-surenb@google.com [surenb@google.com: build fix] Link: https://lkml.kernel.org/r/CAJuCfpFjWhtzRE1X=J+_JjgJzNKhq-=JT8yTBSTHthwp0pqWZw@mail.gmail.com Link: https://lkml.kernel.org/r/20230227173632.3292573-16-surenb@google.comSigned-off-by:
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Suren Baghdasaryan authored
vma_prepare() acquires all locks required before VMA modifications. Move vma_prepare() before vma_adjust_trans_huge() so that VMA is locked before any modification. Link: https://lkml.kernel.org/r/20230227173632.3292573-15-surenb@google.comSigned-off-by:
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Suren Baghdasaryan authored
Updates to vm_flags have to be done with VMA marked as being written for preventing concurrent page faults or other modifications. Link: https://lkml.kernel.org/r/20230227173632.3292573-14-surenb@google.comSigned-off-by:
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Suren Baghdasaryan authored
Introduce per-VMA locking. The lock implementation relies on a per-vma and per-mm sequence counters to note exclusive locking: - read lock - (implemented by vma_start_read) requires the vma (vm_lock_seq) and mm (mm_lock_seq) sequence counters to differ. If they match then there must be a vma exclusive lock held somewhere. - read unlock - (implemented by vma_end_read) is a trivial vma->lock unlock. - write lock - (vma_start_write) requires the mmap_lock to be held exclusively and the current mm counter is assigned to the vma counter. This will allow multiple vmas to be locked under a single mmap_lock write lock (e.g. during vma merging). The vma counter is modified under exclusive vma lock. - write unlock - (vma_end_write_all) is a batch release of all vma locks held. It doesn't pair with a specific vma_start_write! It is done before exclusive mmap_lock is released by incrementing mm sequence counter (mm_lock_seq). - write downgrade - if the mmap_lock is downgraded to the read lock, all vma write locks are released as well (effectivelly same as write unlock). Link: https://lkml.kernel.org/r/20230227173632.3292573-13-surenb@google.comSigned-off-by: -
Suren Baghdasaryan authored
Move mmap_lock assert function definitions up so that they can be used by other mmap_lock routines. Link: https://lkml.kernel.org/r/20230227173632.3292573-12-surenb@google.comSigned-off-by:
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Michel Lespinasse authored
This prepares for page faults handling under VMA lock, looking up VMAs under protection of an rcu read lock, instead of the usual mmap read lock. Link: https://lkml.kernel.org/r/20230227173632.3292573-11-surenb@google.comSigned-off-by:
Michel Lespinasse <michel@lespinasse.org> Signed-off-by:
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Suren Baghdasaryan authored
Patch series "Per-VMA locks", v4. LWN article describing the feature: https://lwn.net/Articles/906852/ Per-vma locks idea that was discussed during SPF [1] discussion at LSF/MM last year [2], which concluded with suggestion that “a reader/writer semaphore could be put into the VMA itself; that would have the effect of using the VMA as a sort of range lock. There would still be contention at the VMA level, but it would be an improvement.” This patchset implements this suggested approach. When handling page faults we lookup the VMA that contains the faulting page under RCU protection and try to acquire its lock. If that fails we fall back to using mmap_lock, similar to how SPF handled this situation. One notable way the implementation deviates from the proposal is the way VMAs are read-locked. During some of mm updates, multiple VMAs need to be locked until the end of the update (e.g. vma_merge, split_vma, etc). Tracking all the locked VMAs, avoiding recursive locks, figuring out when it's safe to unlock previously locked VMAs would make the code more complex. So, instead of the usual lock/unlock pattern, the proposed solution marks a VMA as locked and provides an efficient way to: 1. Identify locked VMAs. 2. Unlock all locked VMAs in bulk. We also postpone unlocking the locked VMAs until the end of the update, when we do mmap_write_unlock. Potentially this keeps a VMA locked for longer than is absolutely necessary but it results in a big reduction of code complexity. Read-locking a VMA is done using two sequence numbers - one in the vm_area_struct and one in the mm_struct. VMA is considered read-locked when these sequence numbers are equal. To read-lock a VMA we set the sequence number in vm_area_struct to be equal to the sequence number in mm_struct. To unlock all VMAs we increment mm_struct's seq number. This allows for an efficient way to track locked VMAs and to drop the locks on all VMAs at the end of the update. The patchset implements per-VMA locking only for anonymous pages which are not in swap and avoids userfaultfs as their implementation is more complex. Additional support for file-back page faults, swapped and user pages can be added incrementally. Performance benchmarks show similar although slightly smaller benefits as with SPF patchset (~75% of SPF benefits). Still, with lower complexity this approach might be more desirable. Since RFC was posted in September 2022, two separate Google teams outside of Android evaluated the patchset and confirmed positive results. Here are the known usecases when per-VMA locks show benefits: Android: Apps with high number of threads (~100) launch times improve by up to 20%. Each thread mmaps several areas upon startup (Stack and Thread-local storage (TLS), thread signal stack, indirect ref table), which requires taking mmap_lock in write mode. Page faults take mmap_lock in read mode. During app launch, both thread creation and page faults establishing the active workinget are happening in parallel and that causes lock contention between mm writers and readers even if updates and page faults are happening in different VMAs. Per-vma locks prevent this contention by providing more granular lock. Google Fibers: We have several dynamically sized thread pools that spawn new threads under increased load and reduce their number when idling. For example, Google's in-process scheduling/threading framework, UMCG/Fibers, is backed by such a thread pool. When idling, only a small number of idle worker threads are available; when a spike of incoming requests arrive, each request is handled in its own "fiber", which is a work item posted onto a UMCG worker thread; quite often these spikes lead to a number of new threads spawning. Each new thread needs to allocate and register an RSEQ section on its TLS, then register itself with the kernel as a UMCG worker thread, and only after that it can be considered by the in-process UMCG/Fiber scheduler as available to do useful work. In short, during an incoming workload spike new threads have to be spawned, and they perform several syscalls (RSEQ registration, UMCG worker registration, memory allocations) before they can actually start doing useful work. Removing any bottlenecks on this thread startup path will greatly improve our services' latencies when faced with request/workload spikes. At high scale, mmap_lock contention during thread creation and stack page faults leads to user-visible multi-second serving latencies in a similar pattern to Android app startup. Per-VMA locking patchset has been run successfully in limited experiments with user-facing production workloads. In these experiments, we observed that the peak thread creation rate was high enough that thread creation is no longer a bottleneck. TCP zerocopy receive: From the point of view of TCP zerocopy receive, the per-vma lock patch is massively beneficial. In today's implementation, a process with N threads where N - 1 are performing zerocopy receive and 1 thread is performing madvise() with the write lock taken (e.g. needs to change vm_flags) will result in all N -1 receive threads blocking until the madvise is done. Conversely, on a busy process receiving a lot of data, an madvise operation that does need to take the mmap lock in write mode will need to wait for all of the receives to be done - a lose:lose proposition. Per-VMA locking _removes_ by definition this source of contention entirely. There are other benefits for receive as well, chiefly a reduction in cacheline bouncing across receiving threads for locking/unlocking the single mmap lock. On an RPC style synthetic workload with 4KB RPCs: 1a) The find+lock+unlock VMA path in the base case, without the per-vma lock patchset, is about 0.7% of cycles as measured by perf. 1b) mmap_read_lock + mmap_read_unlock in the base case is about 0.5% cycles overall - most of this is within the TCP read hotpath (a small fraction is 'other' usage in the system). 2a) The find+lock+unlock VMA path, with the per-vma patchset and a trivial patch written to take advantage of it in TCP, is about 0.4% of cycles (down from 0.7% above) 2b) mmap_read_lock + mmap_read_unlock in the per-vma patchset is < 0.1% cycles and is out of the TCP read hotpath entirely (down from 0.5% before, the remaining usage is the 'other' usage in the system). So, in addition to entirely removing an onerous source of contention, it also reduces the CPU cycles of TCP receive zerocopy by about 0.5%+ (compared to overall cycles in perf) for the 'small' RPC scenario. In https://lkml.kernel.org/r/87fsaqouyd.fsf_-_@stealth, Punit demonstrated throughput improvements of as much as 188% from this patchset. This patch (of 25): This configuration variable will be used to build the support for VMA locking during page fault handling. This is enabled on supported architectures with SMP and MMU set. The architecture support is needed since the page fault handler is called from the architecture's page faulting code which needs modifications to handle faults under VMA lock. Link: https://lkml.kernel.org/r/20230227173632.3292573-1-surenb@google.com Link: https://lkml.kernel.org/r/20230227173632.3292573-10-surenb@google.comSigned-off-by:
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Matthew Wilcox (Oracle) authored
Prevent filesystems from doing things which sleep in their map_pages method. This is in preparation for a pagefault path protected only by RCU. Link: https://lkml.kernel.org/r/20230327174515.1811532-4-willy@infradead.orgSigned-off-by:
Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Darrick J. Wong <djwong@kernel.org> Cc: Dave Chinner <david@fromorbit.com> Cc: David Howells <dhowells@redhat.com> Signed-off-by:
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Matthew Wilcox (Oracle) authored
For the map_pages() method, we need a test that does not sleep. The page fault handler will continue to call the fault() method where we can sleep and do the full revalidation there. Link: https://lkml.kernel.org/r/20230327174515.1811532-3-willy@infradead.orgSigned-off-by:
David Howells <dhowells@redhat.com> Tested-by:
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Matthew Wilcox (Oracle) authored
Patch series "Prevent ->map_pages from sleeping", v2. In preparation for a larger patch series which will handle (some, easy) page faults protected only by RCU, change the two filesystems which have sleeping locks to not take them and hold the RCU lock around calls to ->map_page to prevent other filesystems from adding sleeping locks. This patch (of 3): XFS doesn't actually need to be holding the XFS_MMAPLOCK_SHARED to do this. filemap_map_pages() cannot bring new folios into the page cache and the folio lock is taken during filemap_map_pages() which provides sufficient protection against a truncation or hole punch. Link: https://lkml.kernel.org/r/20230327174515.1811532-1-willy@infradead.org Link: https://lkml.kernel.org/r/20230327174515.1811532-2-willy@infradead.orgSigned-off-by:
Dave Chinner <dchinner@redhat.com> Cc: Darrick J. Wong <djwong@kernel.org> Cc: David Howells <dhowells@redhat.com> Signed-off-by:
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Thomas Weißschuh authored
Since commit ee6d3dd4 ("driver core: make kobj_type constant.") the driver core allows the usage of const struct kobj_type. Take advantage of this to constify the structure definition to prevent modification at runtime. These structures were not constified in commit e56397e8 ("mm/damon/sysfs: make kobj_type structures constant") as they didn't exist when that patch was written. Link: https://lkml.kernel.org/r/20230324-b4-kobj_type-damon2-v1-1-48ddbf1c8fcf@weissschuh.netSigned-off-by:
Thomas Weißschuh <linux@weissschuh.net> Reviewed-by:
SeongJae Park <sj@kernel.org> Reviewed-by:
Muhammad Usama Anjum <usama.anjum@collabora.com> Signed-off-by:
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Chaitanya S Prakash authored
The kernel's default behaviour is to obstruct the allocation of high virtual address as it handles memory overcommit in a heuristic manner. Setting the parameter as OVERCOMMIT_ALWAYS, ensures kernel isn't susceptible to the availability of a platform's physical memory when denying a memory allocation request. Link: https://lkml.kernel.org/r/20230323060121.1175830-4-chaitanyas.prakash@arm.comSigned-off-by:
Chaitanya S Prakash <chaitanyas.prakash@arm.com> Cc: David Hildenbrand <david@redhat.com> Cc: Shuah Khan <shuah@kernel.org> Signed-off-by:
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Chaitanya S Prakash authored
Although there is a provision for 52 bit VA on arm64 platform, it remains unutilised and higher addresses are not allocated. In order to accommodate 4PB [2^52] virtual address space where supported, NR_CHUNKS_HIGH is changed accordingly. Array holding addresses is changed from static allocation to dynamic allocation to accommodate its voluminous nature which otherwise might overflow the stack. Link: https://lkml.kernel.org/r/20230323060121.1175830-3-chaitanyas.prakash@arm.comSigned-off-by:
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Chaitanya S Prakash authored
Patch series "selftests: Fix virtual address range for arm64", v2. When the virtual address range selftest is run on arm64 and x86 platforms, it is observed that both the low and high VA range iterations are skipped when the MAP_CHUNK_SIZE is set to 16GB. The MAP_CHUNK_SIZE is changed to 1GB to resolve this issue, following which support for arm64 platform is added by changing the NR_CHUNKS_HIGH for aarch64 to accommodate up to 4PB of virtual address space allocation requests. Dynamic memory allocation of array holding addresses is introduced to prevent overflow of the stack. Finally, the overcommit_policy is set as OVERCOMMIT_ALWAYS to prevent the kernel from denying a memory allocation request based on a platform's physical memory availability. This patch (of 3): mmap() fails to allocate 16GB virtual space chunk, skipping both low and high VA range iterations. Hence, reduce MAP_CHUNK_SIZE to 1GB and update relevant macros as required. Link: https://lkml.kernel.org/r/20230323060121.1175830-1-chaitanyas.prakash@arm.com Link: https://lkml.kernel.org/r/20230323060121.1175830-2-chaitanyas.prakash@arm.comSigned-off-by:
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Wenchao Hao authored
After commit cb6c33d4 ("cma: tracing: print alloc result in trace_cma_alloc_finish"), cma_alloc_class has only one event which is cma_alloc_busy_retry. So we can remove the cma_alloc_class. Link: https://lkml.kernel.org/r/20230323114136.177677-1-haowenchao2@huawei.comSigned-off-by:
Wenchao Hao <haowenchao2@huawei.com> Acked-by:
Steven Rostedt (Google) <rostedt@goodmis.org> Cc: Feilong Lin <linfeilong@huawei.com> Cc: Hongxiang Lou <louhongxiang@huawei.com> Cc: Masami Hiramatsu <mhiramat@kernel.org> Signed-off-by:
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Tomas Krcka authored
Turn a pr_info() into a pr_debug() to prevent dmesg spamming on systems where memory hotplug is a frequent operation. Link: https://lkml.kernel.org/r/20230323174349.35990-1-krckatom@amazon.deSigned-off-by:
Tomas Krcka <krckatom@amazon.de> Suggested-by:
Jan H. Schönherr <jschoenh@amazon.de> Acked-by:
Pasha Tatashin <pasha.tatashin@soleen.com> Signed-off-by:
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Lorenzo Stoakes authored
Rather than setting err = -1 and only resetting if we hit merge cases, explicitly check the non-mergeable case to make it abundantly clear that we only proceed with the rest if something is mergeable, default err to 0 and only update if an error might occur. Move the merge_prev, merge_next cases closer to the logic determining curr, next and reorder initial variables so they are more logically grouped. This has no functional impact. Link: https://lkml.kernel.org/r/99259fbc6403e80e270e1cc4612abbc8620b121b.1679516210.git.lstoakes@gmail.comSigned-off-by:
Lorenzo Stoakes <lstoakes@gmail.com> Reviewed-by:
Vlastimil Babka <vbabka@suse.cz> Cc: David Hildenbrand <david@redhat.com> Cc: Liam R. Howlett <Liam.Howlett@oracle.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Vernon Yang <vernon2gm@gmail.com> Signed-off-by:
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Lorenzo Stoakes authored
Previously, vma was an uninitialised variable which was only definitely assigned as a result of the logic covering all possible input cases - for it to have remained uninitialised, prev would have to be NULL, and next would _have_ to be mergeable. The value of res defaults to NULL, so we can neatly eliminate the assignment to res and vma in the if (prev) block and ensure that both res and vma are both explicitly assigned, by just setting both to prev. In addition we add an explanation as to under what circumstances both might change, and since we absolutely do rely on addr == curr->vm_start should curr exist, assert that this is the case. Link: https://lkml.kernel.org/r/83938bed24422cbe5954bbf491341674becfe567.1679516210.git.lstoakes@gmail.comSigned-off-by:
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Lorenzo Stoakes authored
Use find_vma_intersection() and vma_lookup() to both simplify the logic and to fold the end == next->vm_start condition into one block. This groups all of the simple range checks together and establishes the invariant that, if prev, curr or next are non-NULL then their positions are as expected. This has no functional impact. Link: https://lkml.kernel.org/r/c6d960641b4ba58fa6ad3d07bf68c27d847963c8.1679516210.git.lstoakes@gmail.comSigned-off-by:
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