| Message ID | 20250213224655.1680278-1-surenb@google.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | reimplement per-vma lock as a refcount | expand |
On 2/14/2025 4:16 AM, Suren Baghdasaryan wrote: > Back when per-vma locks were introduces, vm_lock was moved out of > vm_area_struct in [1] because of the performance regression caused by > false cacheline sharing. Recent investigation [2] revealed that the > regressions is limited to a rather old Broadwell microarchitecture and > even there it can be mitigated by disabling adjacent cacheline > prefetching, see [3]. > Splitting single logical structure into multiple ones leads to more > complicated management, extra pointer dereferences and overall less > maintainable code. When that split-away part is a lock, it complicates > things even further. With no performance benefits, there are no reasons > for this split. Merging the vm_lock back into vm_area_struct also allows > vm_area_struct to use SLAB_TYPESAFE_BY_RCU later in this patchset. > This patchset: > 1. moves vm_lock back into vm_area_struct, aligning it at the cacheline > boundary and changing the cache to be cacheline-aligned to minimize > cacheline sharing; > 2. changes vm_area_struct initialization to mark new vma as detached until > it is inserted into vma tree; > 3. replaces vm_lock and vma->detached flag with a reference counter; > 4. regroups vm_area_struct members to fit them into 3 cachelines; > 5. changes vm_area_struct cache to SLAB_TYPESAFE_BY_RCU to allow for their > reuse and to minimize call_rcu() calls. > > Pagefault microbenchmarks show performance improvement: > Hmean faults/cpu-1 507926.5547 ( 0.00%) 506519.3692 * -0.28%* > Hmean faults/cpu-4 479119.7051 ( 0.00%) 481333.6802 * 0.46%* > Hmean faults/cpu-7 452880.2961 ( 0.00%) 455845.6211 * 0.65%* > Hmean faults/cpu-12 347639.1021 ( 0.00%) 352004.2254 * 1.26%* > Hmean faults/cpu-21 200061.2238 ( 0.00%) 229597.0317 * 14.76%* > Hmean faults/cpu-30 145251.2001 ( 0.00%) 164202.5067 * 13.05%* > Hmean faults/cpu-48 106848.4434 ( 0.00%) 120641.5504 * 12.91%* > Hmean faults/cpu-56 92472.3835 ( 0.00%) 103464.7916 * 11.89%* > Hmean faults/sec-1 507566.1468 ( 0.00%) 506139.0811 * -0.28%* > Hmean faults/sec-4 1880478.2402 ( 0.00%) 1886795.6329 * 0.34%* > Hmean faults/sec-7 3106394.3438 ( 0.00%) 3140550.7485 * 1.10%* > Hmean faults/sec-12 4061358.4795 ( 0.00%) 4112477.0206 * 1.26%* > Hmean faults/sec-21 3988619.1169 ( 0.00%) 4577747.1436 * 14.77%* > Hmean faults/sec-30 3909839.5449 ( 0.00%) 4311052.2787 * 10.26%* > Hmean faults/sec-48 4761108.4691 ( 0.00%) 5283790.5026 * 10.98%* > Hmean faults/sec-56 4885561.4590 ( 0.00%) 5415839.4045 * 10.85%* I tested this patch-series on AMD EPYC Zen 5 system (2-socket, 64-core per socket with SMT Enabled, 4 NUMA nodes) using mmtests's PFT (config-workload-pft-threads) on mm-unstable. I see significant performance improvement for higher thread count: mm-unstable mm-unstable -6.14-rc2-vanilla1 -6.14-rc2-v10-per-vma-lock Hmean faults/cpu-1 1933589.0920 ( 0.00%) 1950506.1985 ( 0.87%) Hmean faults/cpu-4 722834.4269 ( 0.00%) 657946.3257 ( -8.98%) Hmean faults/cpu-7 373210.8410 ( 0.00%) 358995.9493 ( -3.81%) Hmean faults/cpu-12 216267.7580 ( 0.00%) 211032.8119 ( -2.42%) Hmean faults/cpu-21 153080.2758 ( 0.00%) 150207.3115 ( -1.88%) Hmean faults/cpu-30 143142.8874 ( 0.00%) 142904.3981 ( -0.17%) Hmean faults/cpu-48 135825.2524 ( 0.00%) 158502.4303 * 16.70%* Hmean faults/cpu-79 111892.4921 ( 0.00%) 141725.6864 * 26.66%* Hmean faults/cpu-110 96905.8995 ( 0.00%) 114238.6961 * 17.89%* Hmean faults/cpu-128 89136.8524 ( 0.00%) 107620.7035 * 20.74%* Hmean faults/sec-1 1933283.3273 ( 0.00%) 1950224.2371 ( 0.88%) Hmean faults/sec-4 2859235.5825 ( 0.00%) 2611293.1103 ( -8.67%) Hmean faults/sec-7 2580415.8792 ( 0.00%) 2497936.1104 ( -3.20%) Hmean faults/sec-12 2560172.2303 ( 0.00%) 2516697.9056 ( -1.70%) Hmean faults/sec-21 3080686.9599 ( 0.00%) 3038393.3328 ( -1.37%) Hmean faults/sec-30 4174290.0462 ( 0.00%) 4168318.6202 ( -0.14%) Hmean faults/sec-48 6318251.1880 ( 0.00%) 7323087.0849 * 15.90%* Hmean faults/sec-79 8502378.1341 ( 0.00%) 10761979.4193 * 26.58%* Hmean faults/sec-110 10131823.3341 ( 0.00%) 12318722.2392 * 21.58%* Hmean faults/sec-128 10584693.5966 ( 0.00%) 13354652.5141 * 26.17%* Slight degradation at 4 and 7 can be ignored due to high variance: HCoeffVar faults/cpu-4 8.7568 ( 0.00%) 11.4420 ( -30.66%) HCoeffVar faults/cpu-7 3.3204 ( 0.00%) 3.4852 ( -4.96%) Please consider my: Tested-by: Shivank Garg <shivankg@amd.com> Best Regards, Shivank Garg > > Changes since v9 [4]: > PATCH [4/18] > - Change VM_BUG_ON_VMA() to WARN_ON_ONCE() in vma_assert_{attached|detached}, > per Lorenzo Stoakes > - Rename vma_iter_store() into vma_iter_store_new(), per Lorenzo Stoakes > - Expand changelog, per Lorenzo Stoakes > - Update vma tests to check for vma detached state correctness, > per Lorenzo Stoakes > > PATCH [5/18] > - Add Reviewed-by, per Lorenzo Stoakes > > PATCH [6/18] > - Add Acked-by, per Lorenzo Stoakes > > PATCH [7/18] > - Refactor the code, per Lorenzo Stoakes > - Remove Vlastimil's Acked-by since code is changed > > PATCH [8/18] > - Drop inline for mmap_init_lock(), per Lorenzo Stoakes > - Add Reviewed-by, per Lorenzo Stoakes > > PATCH [9/18] > - Add Reviewed-by, per Lorenzo Stoakes > > PATCH [10/18] > - New patch to add refcount_add_not_zero_acquire/refcount_set_release > - Add Acked-by #slab, per Vlastimil Babka > > PATCH [11/18] > - Change refcount limit to be used with xxx_acquire functions > > PATCH [12/18] > - Use __refcount_inc_not_zero_limited_acquire() in vma_start_read(), > per Hillf Danton > - Refactor vma_assert_locked() to avoid vm_refcnt read when CONFIG_DEBUG_VM=n, > per Mateusz Guzik > - Update changelog, per Wei Yang > - Change vma_start_read() to return EAGAIN if vma got isolated and changed > lock_vma_under_rcu() back to detect this condition, per Wei Yang > - Change VM_BUG_ON_VMA() to WARN_ON_ONCE() when checking vma detached state, > per Lorenzo Stoakes > - Remove Vlastimil's Reviewed-by since code is changed > > PATCH [13/18] > - Update vm_area_struct for tests, per Lorenzo Stoakes > - Add Reviewed-by, per Lorenzo Stoakes > > PATCH [14/18] > - Minimized duplicate code, per Lorenzo Stoakes > > PATCH [15/18] > - Add Reviewed-by, per Lorenzo Stoakes > > PATCH [17/18] > - Use refcount_set_release() in vma_mark_attached(), per Will Deacon > > PATCH [18/18] > - Updated documenation, per Lorenzo Stoakes > - Add Reviewed-by, per Lorenzo Stoakes > > [1] https://lore.kernel.org/all/20230227173632.3292573-34-surenb@google.com/ > [2] https://lore.kernel.org/all/ZsQyI%2F087V34JoIt@xsang-OptiPlex-9020/ > [3] https://lore.kernel.org/all/CAJuCfpEisU8Lfe96AYJDZ+OM4NoPmnw9bP53cT_kbfP_pR+-2g@mail.gmail.com/ > [4] https://lore.kernel.org/all/20250111042604.3230628-1-surenb@google.com/ > > Patchset applies over mm-unstable > > Suren Baghdasaryan (18): > mm: introduce vma_start_read_locked{_nested} helpers > mm: move per-vma lock into vm_area_struct > mm: mark vma as detached until it's added into vma tree > mm: introduce vma_iter_store_attached() to use with attached vmas > mm: mark vmas detached upon exit > types: move struct rcuwait into types.h > mm: allow vma_start_read_locked/vma_start_read_locked_nested to fail > mm: move mmap_init_lock() out of the header file > mm: uninline the main body of vma_start_write() > refcount: provide ops for cases when object's memory can be reused > refcount: introduce __refcount_{add|inc}_not_zero_limited_acquire > mm: replace vm_lock and detached flag with a reference count > mm: move lesser used vma_area_struct members into the last cacheline > mm/debug: print vm_refcnt state when dumping the vma > mm: remove extra vma_numab_state_init() call > mm: prepare lock_vma_under_rcu() for vma reuse possibility > mm: make vma cache SLAB_TYPESAFE_BY_RCU > docs/mm: document latest changes to vm_lock > > Documentation/RCU/whatisRCU.rst | 10 + > Documentation/core-api/refcount-vs-atomic.rst | 37 +++- > Documentation/mm/process_addrs.rst | 44 +++-- > include/linux/mm.h | 176 ++++++++++++++---- > include/linux/mm_types.h | 75 ++++---- > include/linux/mmap_lock.h | 6 - > include/linux/rcuwait.h | 13 +- > include/linux/refcount.h | 125 +++++++++++++ > include/linux/slab.h | 15 +- > include/linux/types.h | 12 ++ > kernel/fork.c | 129 ++++++------- > mm/debug.c | 6 + > mm/init-mm.c | 1 + > mm/memory.c | 106 ++++++++++- > mm/mmap.c | 3 +- > mm/nommu.c | 4 +- > mm/userfaultfd.c | 38 ++-- > mm/vma.c | 27 ++- > mm/vma.h | 15 +- > tools/include/linux/refcount.h | 5 + > tools/testing/vma/linux/atomic.h | 6 + > tools/testing/vma/vma.c | 42 ++++- > tools/testing/vma/vma_internal.h | 127 ++++++------- > 23 files changed, 702 insertions(+), 320 deletions(-) > > > base-commit: 47aa60e930fe7fc2a945e4406e3ad1dfa73bb47c
Back when per-vma locks were introduces, vm_lock was moved out of vm_area_struct in [1] because of the performance regression caused by false cacheline sharing. Recent investigation [2] revealed that the regressions is limited to a rather old Broadwell microarchitecture and even there it can be mitigated by disabling adjacent cacheline prefetching, see [3]. Splitting single logical structure into multiple ones leads to more complicated management, extra pointer dereferences and overall less maintainable code. When that split-away part is a lock, it complicates things even further. With no performance benefits, there are no reasons for this split. Merging the vm_lock back into vm_area_struct also allows vm_area_struct to use SLAB_TYPESAFE_BY_RCU later in this patchset. This patchset: 1. moves vm_lock back into vm_area_struct, aligning it at the cacheline boundary and changing the cache to be cacheline-aligned to minimize cacheline sharing; 2. changes vm_area_struct initialization to mark new vma as detached until it is inserted into vma tree; 3. replaces vm_lock and vma->detached flag with a reference counter; 4. regroups vm_area_struct members to fit them into 3 cachelines; 5. changes vm_area_struct cache to SLAB_TYPESAFE_BY_RCU to allow for their reuse and to minimize call_rcu() calls. Pagefault microbenchmarks show performance improvement: Hmean faults/cpu-1 507926.5547 ( 0.00%) 506519.3692 * -0.28%* Hmean faults/cpu-4 479119.7051 ( 0.00%) 481333.6802 * 0.46%* Hmean faults/cpu-7 452880.2961 ( 0.00%) 455845.6211 * 0.65%* Hmean faults/cpu-12 347639.1021 ( 0.00%) 352004.2254 * 1.26%* Hmean faults/cpu-21 200061.2238 ( 0.00%) 229597.0317 * 14.76%* Hmean faults/cpu-30 145251.2001 ( 0.00%) 164202.5067 * 13.05%* Hmean faults/cpu-48 106848.4434 ( 0.00%) 120641.5504 * 12.91%* Hmean faults/cpu-56 92472.3835 ( 0.00%) 103464.7916 * 11.89%* Hmean faults/sec-1 507566.1468 ( 0.00%) 506139.0811 * -0.28%* Hmean faults/sec-4 1880478.2402 ( 0.00%) 1886795.6329 * 0.34%* Hmean faults/sec-7 3106394.3438 ( 0.00%) 3140550.7485 * 1.10%* Hmean faults/sec-12 4061358.4795 ( 0.00%) 4112477.0206 * 1.26%* Hmean faults/sec-21 3988619.1169 ( 0.00%) 4577747.1436 * 14.77%* Hmean faults/sec-30 3909839.5449 ( 0.00%) 4311052.2787 * 10.26%* Hmean faults/sec-48 4761108.4691 ( 0.00%) 5283790.5026 * 10.98%* Hmean faults/sec-56 4885561.4590 ( 0.00%) 5415839.4045 * 10.85%* Changes since v9 [4]: PATCH [4/18] - Change VM_BUG_ON_VMA() to WARN_ON_ONCE() in vma_assert_{attached|detached}, per Lorenzo Stoakes - Rename vma_iter_store() into vma_iter_store_new(), per Lorenzo Stoakes - Expand changelog, per Lorenzo Stoakes - Update vma tests to check for vma detached state correctness, per Lorenzo Stoakes PATCH [5/18] - Add Reviewed-by, per Lorenzo Stoakes PATCH [6/18] - Add Acked-by, per Lorenzo Stoakes PATCH [7/18] - Refactor the code, per Lorenzo Stoakes - Remove Vlastimil's Acked-by since code is changed PATCH [8/18] - Drop inline for mmap_init_lock(), per Lorenzo Stoakes - Add Reviewed-by, per Lorenzo Stoakes PATCH [9/18] - Add Reviewed-by, per Lorenzo Stoakes PATCH [10/18] - New patch to add refcount_add_not_zero_acquire/refcount_set_release - Add Acked-by #slab, per Vlastimil Babka PATCH [11/18] - Change refcount limit to be used with xxx_acquire functions PATCH [12/18] - Use __refcount_inc_not_zero_limited_acquire() in vma_start_read(), per Hillf Danton - Refactor vma_assert_locked() to avoid vm_refcnt read when CONFIG_DEBUG_VM=n, per Mateusz Guzik - Update changelog, per Wei Yang - Change vma_start_read() to return EAGAIN if vma got isolated and changed lock_vma_under_rcu() back to detect this condition, per Wei Yang - Change VM_BUG_ON_VMA() to WARN_ON_ONCE() when checking vma detached state, per Lorenzo Stoakes - Remove Vlastimil's Reviewed-by since code is changed PATCH [13/18] - Update vm_area_struct for tests, per Lorenzo Stoakes - Add Reviewed-by, per Lorenzo Stoakes PATCH [14/18] - Minimized duplicate code, per Lorenzo Stoakes PATCH [15/18] - Add Reviewed-by, per Lorenzo Stoakes PATCH [17/18] - Use refcount_set_release() in vma_mark_attached(), per Will Deacon PATCH [18/18] - Updated documenation, per Lorenzo Stoakes - Add Reviewed-by, per Lorenzo Stoakes [1] https://lore.kernel.org/all/20230227173632.3292573-34-surenb@google.com/ [2] https://lore.kernel.org/all/ZsQyI%2F087V34JoIt@xsang-OptiPlex-9020/ [3] https://lore.kernel.org/all/CAJuCfpEisU8Lfe96AYJDZ+OM4NoPmnw9bP53cT_kbfP_pR+-2g@mail.gmail.com/ [4] https://lore.kernel.org/all/20250111042604.3230628-1-surenb@google.com/ Patchset applies over mm-unstable Suren Baghdasaryan (18): mm: introduce vma_start_read_locked{_nested} helpers mm: move per-vma lock into vm_area_struct mm: mark vma as detached until it's added into vma tree mm: introduce vma_iter_store_attached() to use with attached vmas mm: mark vmas detached upon exit types: move struct rcuwait into types.h mm: allow vma_start_read_locked/vma_start_read_locked_nested to fail mm: move mmap_init_lock() out of the header file mm: uninline the main body of vma_start_write() refcount: provide ops for cases when object's memory can be reused refcount: introduce __refcount_{add|inc}_not_zero_limited_acquire mm: replace vm_lock and detached flag with a reference count mm: move lesser used vma_area_struct members into the last cacheline mm/debug: print vm_refcnt state when dumping the vma mm: remove extra vma_numab_state_init() call mm: prepare lock_vma_under_rcu() for vma reuse possibility mm: make vma cache SLAB_TYPESAFE_BY_RCU docs/mm: document latest changes to vm_lock Documentation/RCU/whatisRCU.rst | 10 + Documentation/core-api/refcount-vs-atomic.rst | 37 +++- Documentation/mm/process_addrs.rst | 44 +++-- include/linux/mm.h | 176 ++++++++++++++---- include/linux/mm_types.h | 75 ++++---- include/linux/mmap_lock.h | 6 - include/linux/rcuwait.h | 13 +- include/linux/refcount.h | 125 +++++++++++++ include/linux/slab.h | 15 +- include/linux/types.h | 12 ++ kernel/fork.c | 129 ++++++------- mm/debug.c | 6 + mm/init-mm.c | 1 + mm/memory.c | 106 ++++++++++- mm/mmap.c | 3 +- mm/nommu.c | 4 +- mm/userfaultfd.c | 38 ++-- mm/vma.c | 27 ++- mm/vma.h | 15 +- tools/include/linux/refcount.h | 5 + tools/testing/vma/linux/atomic.h | 6 + tools/testing/vma/vma.c | 42 ++++- tools/testing/vma/vma_internal.h | 127 ++++++------- 23 files changed, 702 insertions(+), 320 deletions(-) base-commit: 47aa60e930fe7fc2a945e4406e3ad1dfa73bb47c