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

Uladzislau Rezki
2023-09-04T14:56:02Z

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 even though it is a bit outdated(it follows v1), it still gives a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