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Message-ID: <5e19ec93-8307-47c2-bb13-3ddf7150624e@amd.com>
Date: Sat, 15 Feb 2025 01:04:11 +0530
From: Shivank Garg <shivankg@....com>
To: Suren Baghdasaryan <surenb@...gle.com>, akpm@...ux-foundation.org
Cc: peterz@...radead.org, willy@...radead.org, liam.howlett@...cle.com,
lorenzo.stoakes@...cle.com, david.laight.linux@...il.com, mhocko@...e.com,
vbabka@...e.cz, hannes@...xchg.org, mjguzik@...il.com,
oliver.sang@...el.com, mgorman@...hsingularity.net, david@...hat.com,
peterx@...hat.com, oleg@...hat.com, dave@...olabs.net, paulmck@...nel.org,
brauner@...nel.org, dhowells@...hat.com, hdanton@...a.com, hughd@...gle.com,
lokeshgidra@...gle.com, minchan@...gle.com, jannh@...gle.com,
shakeel.butt@...ux.dev, souravpanda@...gle.com, pasha.tatashin@...een.com,
klarasmodin@...il.com, richard.weiyang@...il.com, corbet@....net,
linux-doc@...r.kernel.org, linux-mm@...ck.org, linux-kernel@...r.kernel.org,
kernel-team@...roid.com
Subject: Re: [PATCH v10 00/18] reimplement per-vma lock as a refcount
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@....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
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