[PATCH v2 0/9] Mitigate a vmap lock contention v2

Uladzislau Rezki (Sony)
2023-08-29T08:12:38Z

Hello, folk!

This is the v2, the series which tends to minimize the vmap
lock contention. It is based on the tag: v6.5-rc6. Here you
can find a documentation about it:

wget ftp://vps418301.ovh.net/incoming/Fix_a_vmalloc_lock_contention_in_SMP_env_v2.pdf

even though it is a bit outdated(it follows v1), it still gives a
good overview on the problem and how it can be solved. On demand
and by request i can update it.

The v1 is here: https://lore.kernel.org/linux-mm/ZIAqojPKjChJTssg@pc636/T/

Delta v1 -> v2:
- open coded locking;
- switch to array of nodes instead of per-cpu definition;
- density is 2 cores per one node(not equal to number of CPUs);
- VAs first go back(free path) to an owner node and later to
a global heap if a block is fully freed, nid is saved in va->flags;
- add helpers to drain lazily-freed areas faster, if high pressure;
- picked al Reviewed-by.

Test on AMD Ryzen Threadripper 3970X 32-Core Processor:
sudo ./test_vmalloc.sh run_test_mask=127 nr_threads=64

<v6.5-rc6 perf>
94.17% 0.90% [kernel] [k] _raw_spin_lock
93.27% 93.05% [kernel] [k] native_queued_spin_lock_slowpath
74.69% 0.25% [kernel] [k] __vmalloc_node_range
72.64% 0.01% [kernel] [k] __get_vm_area_node
72.04% 0.89% [kernel] [k] alloc_vmap_area
42.17% 0.00% [kernel] [k] vmalloc
32.53% 0.00% [kernel] [k] __vmalloc_node
24.91% 0.25% [kernel] [k] vfree
24.32% 0.01% [kernel] [k] remove_vm_area
22.63% 0.21% [kernel] [k] find_unlink_vmap_area
15.51% 0.00% [unknown] [k] 0xffffffffc09a74ac
14.35% 0.00% [kernel] [k] ret_from_fork_asm
14.35% 0.00% [kernel] [k] ret_from_fork
14.35% 0.00% [kernel] [k] kthread
<v6.5-rc6 perf>
vs
<v6.5-rc6+v2 perf>
74.32% 2.42% [kernel] [k] __vmalloc_node_range
69.58% 0.01% [kernel] [k] vmalloc
54.21% 1.17% [kernel] [k] __alloc_pages_bulk
48.13% 47.91% [kernel] [k] clear_page_orig
43.60% 0.01% [unknown] [k] 0xffffffffc082f16f
32.06% 0.00% [kernel] [k] ret_from_fork_asm
32.06% 0.00% [kernel] [k] ret_from_fork
32.06% 0.00% [kernel] [k] kthread
31.30% 0.00% [unknown] [k] 0xffffffffc082f889
22.98% 4.16% [kernel] [k] vfree
14.36% 0.28% [kernel] [k] __get_vm_area_node
13.43% 3.35% [kernel] [k] alloc_vmap_area
10.86% 0.04% [kernel] [k] remove_vm_area
8.89% 2.75% [kernel] [k] _raw_spin_lock
7.19% 0.00% [unknown] [k] 0xffffffffc082fba3
6.65% 1.37% [kernel] [k] free_unref_page
6.13% 6.11% [kernel] [k] native_queued_spin_lock_slowpath
<v6.5-rc6+v2 perf>

On smaller systems, for example, 8xCPU Hikey960 board the
contention is not that high and is approximately ~16 percent.

Uladzislau Rezki (Sony) (9):
mm: vmalloc: Add va_alloc() helper
mm: vmalloc: Rename adjust_va_to_fit_type() function
mm: vmalloc: Move vmap_init_free_space() down in vmalloc.c
mm: vmalloc: Remove global vmap_area_root rb-tree
mm: vmalloc: Remove global purge_vmap_area_root rb-tree
mm: vmalloc: Offload free_vmap_area_lock lock
mm: vmalloc: Support multiple nodes in vread_iter
mm: vmalloc: Support multiple nodes in vmallocinfo
mm: vmalloc: Set nr_nodes/node_size based on CPU-cores

mm/vmalloc.c | 929 +++++++++++++++++++++++++++++++++++++--------------
1 file changed, 683 insertions(+), 246 deletions(-)

--
2.30.2