linux-kernel - Re: [PATCH v2 0/9] Mitigate a vmap lock contention v2

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Date:   Wed, 6 Sep 2023 21:04:26 +0100
From:   Lorenzo Stoakes <lstoakes@...il.com>
To:     "Uladzislau Rezki (Sony)" <urezki@...il.com>
Cc:     linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>, Baoquan He <bhe@...hat.com>,
        Christoph Hellwig <hch@...radead.org>,
        Matthew Wilcox <willy@...radead.org>,
        "Liam R . Howlett" <Liam.Howlett@...cle.com>,
        Dave Chinner <david@...morbit.com>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Oleksiy Avramchenko <oleksiy.avramchenko@...y.com>
Subject: Re: [PATCH v2 0/9] Mitigate a vmap lock contention v2

On Tue, Aug 29, 2023 at 10:11:33AM +0200, Uladzislau Rezki (Sony) wrote:
> 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:

Will take a look when I get a chance at v3 as I gather you're spinning
another version :)

Cheers!

>
> 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 even though it is a bit outdated(it follows v1), it still gives a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
>