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

[Uladzislau Rezki <urezki@gmail.com>]

Hello, Andrew!

> 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 even though it is a bit outdated(it follows v1), it still gives a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
> 
It would be good if this series somehow could be tested having some runtime
from the people. So far there was a warning from the test robot:

https://lore.kernel.org/lkml/202308292228.RRrGUYyB-lkp@intel.com/T/#m397b3834cb3b7a0a53b8dffb3624384c8e278007

<snip>
urezki@pc638:~/data/raid0/coding/linux.git$ git diff
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 08990f630c21..7105d7bcd37e 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -4778,7 +4778,7 @@ static void vmap_init_free_space(void)
         *  |<--------------------------------->|
         */
        for (busy = vmlist; busy; busy = busy->next) {
-               if (busy->addr - vmap_start > 0) {
+               if ((unsigned long) busy->addr - vmap_start > 0) {
                        free = kmem_cache_zalloc(vmap_area_cachep, GFP_NOWAIT);
                        if (!WARN_ON_ONCE(!free)) {
                                free->va_start = vmap_start;
urezki@pc638:~/data/raid0/coding/linux.git$
<snip>

This extra patch has to be applied to fix the warning. 

From my side i have tested it as much as i can. Can it be plugged
into linux-next to get some runtime? Or is there any other way you
prefer to go?

Thank you in advance!

--
Uladzislau Rezki