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Message-ID: <20250111042604.3230628-1-surenb@google.com>
Date: Fri, 10 Jan 2025 20:25:47 -0800
From: Suren Baghdasaryan <surenb@...gle.com>
To: 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, surenb@...gle.com
Subject: [PATCH v9 00/17] reimplement per-vma lock as a refcount
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 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@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/20250109023025.2242447-1-surenb@google.com/
[5] https://lore.kernel.org/all/20241111205506.3404479-5-surenb@google.com/
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(-)
--
2.47.1.613.gc27f4b7a9f-goog
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