Subject: Re: [PATCH net-next v7 0/6] neighbour: Improve neigh_flush_dev performance

From: Stanislav Fomichev <[email-masked]>
Date: Tue, 22 Oct 2024 16:48:40 -0700

On 10/22, Gilad Naaman wrote:
> This patchsets improves the performance of neigh_flush_dev.
> 
> Currently, the only way to implement it requires traversing
> all neighbours known to the kernel, across all network-namespaces.
> 
> This means that some flows are slowed down as a function of neighbour-scale,
> even if the specific link they're handling has little to no neighbours.
> 
> In order to solve this, this patchset adds a netdev->neighbours list,
> as well as making the original linked-list doubly-, so that it is
> possible to unlink neighbours without traversing the hash-bucket to
> obtain the previous neighbour.
> 
> The original use-case we encountered was mass-deletion of links (12K
> VLANs) while there are 50K ARPs and 50K NDPs in the system; though the
> slowdowns would also appear when the links are set down.
> 
> Changes in v7:
> 
>  - Fix crash due to use of poisoned hlist_node
>  - Apply samx-tree formatting
> 
> Gilad Naaman (6):
>   neighbour: Add hlist_node to struct neighbour
>   neighbour: Define neigh_for_each_in_bucket
>   neighbour: Convert seq_file functions to use hlist
>   neighbour: Convert iteration to use hlist+macro
>   neighbour: Remove bare neighbour::next pointer
>   neighbour: Create netdev->neighbour association
> 
>  .../networking/net_cachelines/net_device.rst  |   1 +
>  include/linux/netdevice.h                     |   7 +
>  include/net/neighbour.h                       |  24 +-
>  include/net/neighbour_tables.h                |  12 +
>  net/core/neighbour.c                          | 337 ++++++++----------
>  net/ipv4/arp.c                                |   2 +-
>  6 files changed, 174 insertions(+), 209 deletions(-)
>  create mode 100644 include/net/neighbour_tables.h

Looks like the test is still unhappy. Can you try to run it on your side
before reposting? Or does it look good?

[  110.442590][    C2] page: refcount:1 mapcount:0 mapping:0000000000000000 index:0x1 pfn:0x5191
[  110.443219][    C2] head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
[  110.443498][    C2] flags: 0x80000000000040(head|node=0|zone=1)
[  110.443752][    C2] page_type: f5(slab)
[  110.443897][    C2] raw: 0080000000000003 ffffea0000146401 ffffffffffffffff 0000000000000000
[  110.444236][    C2] raw: 0000000000000008 0000000000000000 00000000ffffffff 0000000000000000
[  110.444546][    C2] head: 0080000000000040 ffff8880010433c0 ffffea0000256410 ffff8880010410e8
[  110.444862][    C2] head: 0000000000000000 0000000000020002 00000001f5000000 0000000000000000
[  110.445175][    C2] head: 0080000000000003 ffffea0000146401 ffffffffffffffff 0000000000000000
[  110.445890][    C2] head: 0000000000000008 0000000000000000 00000000ffffffff 0000000000000000
[  110.446197][    C2] page dumped because: VM_BUG_ON_PAGE(page_ref_count(page) == 0)
[  110.446558][    C2] ------------[ cut here ]------------
[  110.446754][    C2] kernel BUG at include/linux/mm.h:1140!
[  110.446972][    C2] Oops: invalid opcode: 0000 [#1] PREEMPT SMP KASAN NOPTI
[  110.447210][    C2] CPU: 2 UID: 0 PID: 29 Comm: ksoftirqd/2 Not tainted 6.12.0-rc3-virtme #1
[  110.447528][    C2] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[  110.447928][    C2] RIP: 0010:__free_pages+0x1e4/0x220
[  110.448128][    C2] Code: 0f 94 c3 e9 ba fe ff ff 48 c7 c6 a0 18 58 92 4c 89 e7 e8 df bf f4 ff 90 0f 0b 48 c7 c6 40 29 58 92 4c 89 e7 e8 cd bf f4 ff 90 <0f> 0b 48 89 ef e8 72 03 09 00 e9 c5 fe ff ff e8 98 03 09 00 e9 35
[  110.448803][    C2] RSP: 0018:ffffc90000217cb0 EFLAGS: 00010246
[  110.449040][    C2] RAX: 000000000000003e RBX: 0000000000000000 RCX: 1ffffffff263b43c
[  110.449304][    C2] RDX: 0000000000000000 RSI: 0000000000000004 RDI: 0000000000000001
[  110.449565][    C2] RBP: ffffea0000146474 R08: 0000000000000000 R09: fffffbfff263b43c
[  110.449840][    C2] R10: 0000000000000003 R11: 205d324320202020 R12: ffffea0000146440
[  110.450101][    C2] R13: ffffc90000217d78 R14: 0000000000000000 R15: 0000000000000008
[  110.450399][    C2] FS:  0000000000000000(0000) GS:ffff888036100000(0000) knlGS:0000000000000000
[  110.450787][    C2] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  110.451008][    C2] CR2: 00007f9289e72270 CR3: 000000000a73a005 CR4: 0000000000772ef0
[  110.451274][    C2] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  110.451564][    C2] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  110.451860][    C2] PKRU: 55555554
[  110.452015][    C2] Call Trace:
[  110.452167][    C2]  <TASK>
[  110.452282][    C2]  ? die+0x37/0x90
[  110.452440][    C2]  ? do_trap+0x1a3/0x260
[  110.452589][    C2]  ? __free_pages+0x1e4/0x220
[  110.452786][    C2]  ? do_error_trap+0xbe/0x180
[  110.452970][    C2]  ? __free_pages+0x1e4/0x220
[  110.453152][    C2]  ? __free_pages+0x1e4/0x220
[  110.453342][    C2]  ? handle_invalid_op+0x2c/0x40
[  110.453527][    C2]  ? __free_pages+0x1e4/0x220
[  110.453709][    C2]  ? exc_invalid_op+0x30/0x50
[  110.453934][    C2]  ? asm_exc_invalid_op+0x1a/0x20
[  110.454126][    C2]  ? __free_pages+0x1e4/0x220
[  110.454321][    C2]  ? rcu_do_batch+0x34d/0xf20
[  110.454528][    C2]  neigh_hash_free_rcu+0xb7/0xe0
[  110.454728][    C2]  rcu_do_batch+0x34f/0xf20
[  110.454913][    C2]  ? __pfx___lock_release+0x10/0x10
[  110.455108][    C2]  ? __pfx_rcu_do_batch+0x10/0x10
[  110.455350][    C2]  ? lockdep_hardirqs_on_prepare+0x12b/0x410
[  110.455604][    C2]  rcu_core+0x2bd/0x4f0
[  110.455773][    C2]  handle_softirqs+0x1f6/0x5c0
[  110.455965][    C2]  ? __pfx_run_ksoftirqd+0x10/0x10
[  110.456152][    C2]  run_ksoftirqd+0x33/0x60
[  110.456342][    C2]  smpboot_thread_fn+0x306/0x850
[  110.456533][    C2]  ? __pfx_smpboot_thread_fn+0x10/0x10
[  110.456719][    C2]  ? __pfx_smpboot_thread_fn+0x10/0x10
[  110.456903][    C2]  kthread+0x28a/0x350
[  110.457041][    C2]  ? __pfx_kthread+0x10/0x10
[  110.457369][    C2]  ret_from_fork+0x31/0x70
[  110.457566][    C2]  ? __pfx_kthread+0x10/0x10
[  110.457748][    C2]  ret_from_fork_asm+0x1a/0x30
[  110.457944][    C2]  </TASK>

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pw-bot: cr