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From:   Oscar Salvador <osalvador@suse.de>
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        Michal Hocko <mhocko@suse.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Waiman Long <longman@redhat.com>,
        Suren Baghdasaryan <surenb@google.com>,
        Marco Elver <elver@google.com>,
        Andrey Konovalov <andreyknvl@gmail.com>,
        Eric Dumazet <edumazet@google.com>,
        Alexander Potapenko <glider@google.com>,
        Oscar Salvador <osalvador@suse.de>
Subject: [PATCH v5 3/3] mm,page_owner: Filter out stacks by a threshold counter
Date:   Tue, 16 May 2023 20:25:37 +0200
Message-Id: <20230516182537.3139-4-osalvador@suse.de>
In-Reply-To: <20230516182537.3139-1-osalvador@suse.de>
References: <20230516182537.3139-1-osalvador@suse.de>
MIME-Version: 1.0
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We want to be able to filter out the output on a threshold basis,
in this way we can get rid of a lot of noise and focus only on those
stacks which have an allegedly high counter.

We can control the threshold value by a new file called
'page_owner_threshold', which is 0 by default.

Signed-off-by: Oscar Salvador <osalvador@suse.de>
---
 lib/stackdepot.c |  5 ++++-
 mm/page_owner.c  | 21 +++++++++++++++++++++
 2 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/lib/stackdepot.c b/lib/stackdepot.c
index c4af2e946500..7053221ce1d8 100644
--- a/lib/stackdepot.c
+++ b/lib/stackdepot.c
@@ -488,6 +488,9 @@ static struct stack_record *stack_depot_getstack(depot_stack_handle_t handle)
 }
 
 #ifdef CONFIG_PAGE_OWNER
+
+extern unsigned long page_owner_stack_threshold;
+
 void *stack_start(struct seq_file *m, loff_t *ppos)
 {
 	unsigned long *table = m->private;
@@ -543,7 +546,7 @@ int stack_print(struct seq_file *m, void *v)
 
 	if (!stack->size || stack->size < 0 ||
 	    stack->size > PAGE_SIZE || stack->handle.valid != 1 ||
-	    refcount_read(&stack->count) < 1)
+	    refcount_read(&stack->count) < page_owner_stack_threshold)
 		return 0;
 
 	buf = kzalloc(PAGE_SIZE, GFP_KERNEL);
diff --git a/mm/page_owner.c b/mm/page_owner.c
index 2d97f6b34ea6..28c519fc9372 100644
--- a/mm/page_owner.c
+++ b/mm/page_owner.c
@@ -743,6 +743,23 @@ const struct file_operations page_owner_stack_operations = {
 	.release        = seq_release,
 };
 
+unsigned long page_owner_stack_threshold;
+
+int page_owner_threshold_get(void *data, u64 *val)
+{
+	*val = page_owner_stack_threshold;
+	return 0;
+}
+
+int page_owner_threshold_set(void *data, u64 val)
+{
+	page_owner_stack_threshold = val;
+	return 0;
+}
+
+DEFINE_SIMPLE_ATTRIBUTE(proc_page_owner_threshold, &page_owner_threshold_get,
+			&page_owner_threshold_set, "%llu");
+
 static int __init pageowner_init(void)
 {
 	if (!static_branch_unlikely(&page_owner_inited)) {
@@ -755,6 +772,10 @@ static int __init pageowner_init(void)
 
 	debugfs_create_file("page_owner_stacks", 0400, NULL, NULL,
 			     &page_owner_stack_operations);
+	debugfs_create_file("page_owner_threshold", 0600, NULL, NULL,
+			    &proc_page_owner_threshold);
+
+	page_owner_stack_threshold = 0;
 
 	return 0;
 }
-- 
2.35.3