[PATCH v3 10/11] mm: vmalloc: Set nr_nodes based on CPUs in a system

["Uladzislau Rezki (Sony)" <urezki@gmail.com>]

A number of nodes which are used in the alloc/free paths is
set based on num_possible_cpus() in a system. Please note a
high limit threshold though is fixed and corresponds to 128
nodes.

For 32-bit or single core systems an access to a global vmap
heap is not balanced. Such small systems do not suffer from
lock contentions due to low number of CPUs. In such case the
nr_nodes is equal to 1.

Test on AMD Ryzen Threadripper 3970X 32-Core Processor:
sudo ./test_vmalloc.sh run_test_mask=7 nr_threads=64

<default perf>
 94.41%     0.89%  [kernel]        [k] _raw_spin_lock
 93.35%    93.07%  [kernel]        [k] native_queued_spin_lock_slowpath
 76.13%     0.28%  [kernel]        [k] __vmalloc_node_range
 72.96%     0.81%  [kernel]        [k] alloc_vmap_area
 56.94%     0.00%  [kernel]        [k] __get_vm_area_node
 41.95%     0.00%  [kernel]        [k] vmalloc
 37.15%     0.01%  [test_vmalloc]  [k] full_fit_alloc_test
 35.17%     0.00%  [kernel]        [k] ret_from_fork_asm
 35.17%     0.00%  [kernel]        [k] ret_from_fork
 35.17%     0.00%  [kernel]        [k] kthread
 35.08%     0.00%  [test_vmalloc]  [k] test_func
 34.45%     0.00%  [test_vmalloc]  [k] fix_size_alloc_test
 28.09%     0.01%  [test_vmalloc]  [k] long_busy_list_alloc_test
 23.53%     0.25%  [kernel]        [k] vfree.part.0
 21.72%     0.00%  [kernel]        [k] remove_vm_area
 20.08%     0.21%  [kernel]        [k] find_unlink_vmap_area
  2.34%     0.61%  [kernel]        [k] free_vmap_area_noflush
<default perf>
   vs
<patch-series perf>
 82.32%     0.22%  [test_vmalloc]  [k] long_busy_list_alloc_test
 63.36%     0.02%  [kernel]        [k] vmalloc
 63.34%     2.64%  [kernel]        [k] __vmalloc_node_range
 30.42%     4.46%  [kernel]        [k] vfree.part.0
 28.98%     2.51%  [kernel]        [k] __alloc_pages_bulk
 27.28%     0.19%  [kernel]        [k] __get_vm_area_node
 26.13%     1.50%  [kernel]        [k] alloc_vmap_area
 21.72%    21.67%  [kernel]        [k] clear_page_rep
 19.51%     2.43%  [kernel]        [k] _raw_spin_lock
 16.61%    16.51%  [kernel]        [k] native_queued_spin_lock_slowpath
 13.40%     2.07%  [kernel]        [k] free_unref_page
 10.62%     0.01%  [kernel]        [k] remove_vm_area
  9.02%     8.73%  [kernel]        [k] insert_vmap_area
  8.94%     0.00%  [kernel]        [k] ret_from_fork_asm
  8.94%     0.00%  [kernel]        [k] ret_from_fork
  8.94%     0.00%  [kernel]        [k] kthread
  8.29%     0.00%  [test_vmalloc]  [k] test_func
  7.81%     0.05%  [test_vmalloc]  [k] full_fit_alloc_test
  5.30%     4.73%  [kernel]        [k] purge_vmap_node
  4.47%     2.65%  [kernel]        [k] free_vmap_area_noflush
<patch-series perf>

confirms that a native_queued_spin_lock_slowpath goes down to
16.51% percent from 93.07%.

The throughput is ~12x higher:

urezki@pc638:~$ time sudo ./test_vmalloc.sh run_test_mask=7 nr_threads=64
Run the test with following parameters: run_test_mask=7 nr_threads=64
Done.
Check the kernel ring buffer to see the summary.

real    10m51.271s
user    0m0.013s
sys     0m0.187s
urezki@pc638:~$

urezki@pc638:~$ time sudo ./test_vmalloc.sh run_test_mask=7 nr_threads=64
Run the test with following parameters: run_test_mask=7 nr_threads=64
Done.
Check the kernel ring buffer to see the summary.

real    0m51.301s
user    0m0.015s
sys     0m0.040s
urezki@pc638:~$

Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
---
 mm/vmalloc.c | 29 +++++++++++++++++++++++------
 1 file changed, 23 insertions(+), 6 deletions(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 0c671cb96151..ef534c76daef 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -4879,10 +4879,27 @@ static void vmap_init_free_space(void)
 static void vmap_init_nodes(void)
 {
 	struct vmap_node *vn;
-	int i, j;
+	int i, n;
+
+#if BITS_PER_LONG == 64
+	/* A high threshold of max nodes is fixed and bound to 128. */
+	n = clamp_t(unsigned int, num_possible_cpus(), 1, 128);
+
+	if (n > 1) {
+		vn = kmalloc_array(n, sizeof(*vn), GFP_NOWAIT | __GFP_NOWARN);
+		if (vn) {
+			/* Node partition is 16 pages. */
+			vmap_zone_size = (1 << 4) * PAGE_SIZE;
+			nr_vmap_nodes = n;
+			vmap_nodes = vn;
+		} else {
+			pr_err("Failed to allocate an array. Disable a node layer\n");
+		}
+	}
+#endif
 
-	for (i = 0; i < nr_vmap_nodes; i++) {
-		vn = &vmap_nodes[i];
+	for (n = 0; n < nr_vmap_nodes; n++) {
+		vn = &vmap_nodes[n];
 		vn->busy.root = RB_ROOT;
 		INIT_LIST_HEAD(&vn->busy.head);
 		spin_lock_init(&vn->busy.lock);
@@ -4891,9 +4908,9 @@ static void vmap_init_nodes(void)
 		INIT_LIST_HEAD(&vn->lazy.head);
 		spin_lock_init(&vn->lazy.lock);
 
-		for (j = 0; j < MAX_VA_SIZE_PAGES; j++) {
-			INIT_LIST_HEAD(&vn->pool[j].head);
-			WRITE_ONCE(vn->pool[j].len, 0);
+		for (i = 0; i < MAX_VA_SIZE_PAGES; i++) {
+			INIT_LIST_HEAD(&vn->pool[i].head);
+			WRITE_ONCE(vn->pool[i].len, 0);
 		}
 
 		spin_lock_init(&vn->pool_lock);
-- 
2.39.2