On Mon, Jan 27, 2025 at 9:27 PM Shivank Garg <shivankg@xxxxxxx> wrote: > > Hi Suren, > > I tested the 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) benchmark on > mm-unstable. > > On 1/11/2025 9:55 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%* > > Results: > mm-unstable-vanilla mm-unstable-v9-pervma-lock > Hmean faults/cpu-1 2018530.3023 ( 0.00%) 2051456.8039 ( 1.63%) > Hmean faults/cpu-4 718869.0234 ( 0.00%) 720985.6986 ( 0.29%) > Hmean faults/cpu-7 377965.1187 ( 0.00%) 368305.2802 ( -2.56%) > Hmean faults/cpu-12 215502.5334 ( 0.00%) 212764.0061 ( -1.27%) > Hmean faults/cpu-21 149946.1873 ( 0.00%) 150688.2173 ( 0.49%) > Hmean faults/cpu-30 142379.7863 ( 0.00%) 143677.5012 ( 0.91%) > Hmean faults/cpu-48 139625.5003 ( 0.00%) 156217.1383 * 11.88%* > Hmean faults/cpu-79 119093.6132 ( 0.00%) 140501.1787 * 17.98%* > Hmean faults/cpu-110 102446.6879 ( 0.00%) 114128.7155 ( 11.40%) > Hmean faults/cpu-128 96640.4022 ( 0.00%) 109474.8875 ( 13.28%) > Hmean faults/sec-1 2018197.4666 ( 0.00%) 2051119.1375 ( 1.63%) > Hmean faults/sec-4 2853494.9619 ( 0.00%) 2865639.8350 ( 0.43%) > Hmean faults/sec-7 2631049.4283 ( 0.00%) 2564037.1696 ( -2.55%) > Hmean faults/sec-12 2570378.4204 ( 0.00%) 2540353.2525 ( -1.17%) > Hmean faults/sec-21 3018640.3933 ( 0.00%) 3014396.9773 ( -0.14%) > Hmean faults/sec-30 4150723.9209 ( 0.00%) 4167550.4070 ( 0.41%) > Hmean faults/sec-48 6459327.6559 ( 0.00%) 7217660.4385 * 11.74%* > Hmean faults/sec-79 8977397.1421 ( 0.00%) 10695351.6214 * 19.14%* > Hmean faults/sec-110 10590055.2262 ( 0.00%) 12309035.9250 ( 16.23%) > Hmean faults/sec-128 11448246.6485 ( 0.00%) 13554648.3823 ( 18.40%) Hi Shivank, Thank you for providing more test results! This looks quite good! > > Please add my: > Tested-by: Shivank Garg <shivankg@xxxxxxx> > > I would be happy to test future versions if needed. That would be very much appreciated! I'll CC you on the next version. Thanks, Suren. > > Thanks, > Shivank > > > > > > > Changes since v8 [4]: > > - Change subject for the cover letter, per Vlastimil Babka > > - Added Reviewed-by and Acked-by, per Vlastimil Babka > > - Added static check for no-limit case in __refcount_add_not_zero_limited, > > per David Laight > > - Fixed vma_refcount_put() to call rwsem_release() unconditionally, > > per Hillf Danton and Vlastimil Babka > > - Use a copy of vma->vm_mm in vma_refcount_put() in case vma is freed from > > under us, per Vlastimil Babka > > - Removed extra rcu_read_lock()/rcu_read_unlock() in vma_end_read(), > > per Vlastimil Babka > > - Changed __vma_enter_locked() parameter to centralize refcount logic, > > per Vlastimil Babka > > - Amended description in vm_lock replacement patch explaining the effects > > of the patch on vm_area_struct size, per Vlastimil Babka > > - Added vm_area_struct member regrouping patch [5] into the series > > - Renamed vma_copy() into vm_area_init_from(), per Liam R. Howlett > > - Added a comment for vm_area_struct to update vm_area_init_from() when > > adding new members, per Vlastimil Babka > > - Updated a comment about unstable src->shared.rb when copying a vma in > > vm_area_init_from(), per Vlastimil Babka > > > > [1] https://lore.kernel.org/all/20230227173632.3292573-34-surenb@xxxxxxxxxx/ > > [2] https://lore.kernel.org/all/ZsQyI%2F087V34JoIt@xsang-OptiPlex-9020/ > > [3] https://lore.kernel.org/all/CAJuCfpEisU8Lfe96AYJDZ+OM4NoPmnw9bP53cT_kbfP_pR+-2g@xxxxxxxxxxxxxx/ > > [4] https://lore.kernel.org/all/20250109023025.2242447-1-surenb@xxxxxxxxxx/ > > [5] https://lore.kernel.org/all/20241111205506.3404479-5-surenb@xxxxxxxxxx/ > > > > Patchset applies over mm-unstable after reverting v8 > > (current SHA range: 235b5129cb7b - 9e6b24c58985) > > > > Suren Baghdasaryan (17): > > 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: introduce __refcount_{add|inc}_not_zero_limited > > 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/mm/process_addrs.rst | 44 ++++---- > > include/linux/mm.h | 156 ++++++++++++++++++++++------- > > include/linux/mm_types.h | 75 +++++++------- > > include/linux/mmap_lock.h | 6 -- > > include/linux/rcuwait.h | 13 +-- > > include/linux/refcount.h | 24 ++++- > > include/linux/slab.h | 6 -- > > include/linux/types.h | 12 +++ > > kernel/fork.c | 129 +++++++++++------------- > > mm/debug.c | 12 +++ > > mm/init-mm.c | 1 + > > mm/memory.c | 97 ++++++++++++++++-- > > mm/mmap.c | 3 +- > > mm/userfaultfd.c | 32 +++--- > > mm/vma.c | 23 ++--- > > mm/vma.h | 15 ++- > > tools/testing/vma/linux/atomic.h | 5 + > > tools/testing/vma/vma_internal.h | 93 ++++++++--------- > > 18 files changed, 465 insertions(+), 281 deletions(-) > > >
