[PATCH 2/3] mm/page_owner: add compact mode filter

[Zhen Ni]

Add compact mode functionality to reduce page_owner output size by
printing only the stack handle instead of the full stack trace.

Example output:
  Page allocated via order 0, mask 0x42800(GFP_NOWAIT|__GFP_COMP),
  pid 1, tgid 1 (systemd), ts 349667370 ns
  PFN 0xa00a2 type Unmovable Block 1280 type Unmovable
  Flags 0x33fffe0000004124(referenced|lru|active|private|node=3|zone=0|
lastcpupid=0x1ffff)
  handle: 17432583
  Charged to memcg /

Compact mode significantly reduces output size while preserving all
other page allocation information, making it easier to analyze large
volumes of page owner data.The correspondence between handles and stack
traces can be obtained through the show_stacks_handles interface.

Signed-off-by: Zhen Ni <zhen.ni@xxxxxxxxxxxx>
---
 mm/page_owner.c | 29 ++++++++++++++++++++++++++++-
 1 file changed, 28 insertions(+), 1 deletion(-)

diff --git a/mm/page_owner.c b/mm/page_owner.c
index 6811439bf9e4..214b58eef3d8 100644
--- a/mm/page_owner.c
+++ b/mm/page_owner.c
@@ -585,7 +585,14 @@ print_page_owner(char __user *buf, size_t count, unsigned long pfn,
 			migratetype_names[pageblock_mt],
 			&page->flags);
 
-	ret += stack_depot_snprint(handle, kbuf + ret, count - ret, 0);
+	/* Compact mode: print handle instead of full stack trace */
+	if (READ_ONCE(owner_filter.compact)) {
+		ret += scnprintf(kbuf + ret, count - ret,
+				"handle: %d\n", handle);
+	} else {
+		ret += stack_depot_snprint(handle, kbuf + ret, count - ret, 0);
+	}
+
 	if (ret >= count)
 		goto err;
 
@@ -980,6 +987,24 @@ static int page_owner_threshold_set(void *data, u64 val)
 DEFINE_SIMPLE_ATTRIBUTE(page_owner_threshold_fops, &page_owner_threshold_get,
 			&page_owner_threshold_set, "%llu");
 
+static int page_owner_compact_get(void *data, u64 *val)
+{
+	*val = READ_ONCE(owner_filter.compact);
+	return 0;
+}
+
+static int page_owner_compact_set(void *data, u64 val)
+{
+	if (val != 0 && val != 1)
+		return -EINVAL;
+	WRITE_ONCE(owner_filter.compact, val);
+	return 0;
+}
+
+DEFINE_SIMPLE_ATTRIBUTE(page_owner_compact_fops,
+			&page_owner_compact_get,
+			&page_owner_compact_set, "%lld");
+
 
 static int __init pageowner_init(void)
 {
@@ -993,6 +1018,8 @@ static int __init pageowner_init(void)
 	debugfs_create_file("page_owner", 0400, NULL, NULL, &page_owner_fops);
 
 	filter_dir = debugfs_create_dir("page_owner_filter", NULL);
+	debugfs_create_file("compact", 0600, filter_dir, NULL,
+			    &page_owner_compact_fops);
 
 	dir = debugfs_create_dir("page_owner_stacks", NULL);
 	debugfs_create_file("show_stacks", 0400, dir,
-- 
2.20.1