[PATCH v3 09/11] mm, swap: add debugfs counters for vswap

Add /sys/kernel/debug/vswap/ with two counters:

* used: virtual swap slots (pages) currently allocated
* alloc_reject: cumulative pages that failed to get a vswap slot

Signed-off-by: Nhat Pham <[email protected]>
---
 mm/swapfile.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 1a2d9d9625fc..b4d7af21ca1c 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -7,6 +7,7 @@
  */
 
 #include <linux/blkdev.h>
+#include <linux/debugfs.h>
 #include <linux/mm.h>
 #include <linux/sched/mm.h>
 #include <linux/sched/task.h>
@@ -133,6 +134,9 @@ static DEFINE_PER_CPU(struct percpu_swap_cluster, percpu_swap_cluster) = {
 	.lock = INIT_LOCAL_LOCK(),
 };
 
+static atomic_t __maybe_unused vswap_used = ATOMIC_INIT(0);
+static atomic_t __maybe_unused vswap_alloc_reject = ATOMIC_INIT(0);
+
 #ifdef CONFIG_VSWAP
 static int sysctl_vswap_enabled = IS_ENABLED(CONFIG_VSWAP_DEFAULT_ON);
 
@@ -2056,11 +2060,13 @@ static bool vswap_alloc(struct folio *folio)
 	if (folio_test_swapcache(folio)) {
 		/* alloc_swap_scan_cluster updated percpu offset already */
 		local_unlock(&percpu_vswap_cluster.lock);
+		atomic_add(folio_nr_pages(folio), &vswap_used);
 		return true;
 	}
 
 	this_cpu_write(percpu_vswap_cluster.offset[order], SWAP_ENTRY_INVALID);
 	local_unlock(&percpu_vswap_cluster.lock);
+	atomic_add(folio_nr_pages(folio), &vswap_alloc_reject);
 	return false;
 }
 #endif
@@ -2665,8 +2671,10 @@ void __swap_cluster_free_entries(struct swap_info_struct *si,
 
 	VM_WARN_ON(ci->count < nr_pages);
 
-	if (is_vswap)
+	if (is_vswap) {
 		__vswap_release_backing(ci, ci_start, nr_pages);
+		atomic_sub(nr_pages, &vswap_used);
+	}
 
 	ci->count -= nr_pages;
 	do {
@@ -4862,6 +4870,7 @@ static const struct ctl_table vswap_sysctls[] = {
 static int __init vswap_init(void)
 {
 	struct swap_info_struct *si;
+	struct dentry *root;
 	unsigned long maxpages;
 	int err;
 
@@ -4896,6 +4905,10 @@ static int __init vswap_init(void)
 
 	register_sysctl_init("vm", vswap_sysctls);
 
+	root = debugfs_create_dir("vswap", NULL);
+	debugfs_create_atomic_t("used", 0444, root, &vswap_used);
+	debugfs_create_atomic_t("alloc_reject", 0444, root, &vswap_alloc_reject);
+
 	pr_info("vswap: created virtual swap device (%lu pages)\n", maxpages);
 	return 0;
 
-- 
2.53.0-Meta