[PATCH v2] mm: show_mem: show number of zspages in show_free_areas

[Thadeu Lima de Souza Cascardo <cascardo@igalia.com>]

When OOM is triggered, it will show where the pages might be for each zone.
When using zram or zswap, it might look like lots of pages are missing.
After this patch, zspages are shown as below.

[   48.792859] Node 0 DMA free:2812kB boost:0kB min:60kB low:72kB high:84kB reserved_highatomic:0KB free_highatomic:0KB active_anon:0kB inactive_anon:0kB active_file:0kB inactive_file:0kB unevictable:0kB writepending:0kB zspages:11160kB present:15992kB managed:15360kB mlocked:0kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB
[   48.792962] lowmem_reserve[]: 0 956 956 956 956
[   48.792988] Node 0 DMA32 free:3512kB boost:0kB min:3912kB low:4888kB high:5864kB reserved_highatomic:0KB free_highatomic:0KB active_anon:0kB inactive_anon:28kB active_file:8kB inactive_file:16kB unevictable:0kB writepending:0kB zspages:916780kB present:1032064kB managed:978944kB mlocked:0kB bounce:0kB free_pcp:500kB local_pcp:248kB free_cma:0kB
[   48.793118] lowmem_reserve[]: 0 0 0 0 0

Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@igalia.com>
---
v2:
- fix build when CONFIG_ZSMALLOC is not enabled
---
 mm/show_mem.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/mm/show_mem.c b/mm/show_mem.c
index 41999e94a56d623726ea92f3f38785e8b218afe5..c563d9adfa87765a8736e91c1f68d824b03eaea8 100644
--- a/mm/show_mem.c
+++ b/mm/show_mem.c
@@ -310,6 +310,7 @@ static void show_free_areas(unsigned int filter, nodemask_t *nodemask, int max_z
 			" inactive_file:%lukB"
 			" unevictable:%lukB"
 			" writepending:%lukB"
+			" zspages:%lukB"
 			" present:%lukB"
 			" managed:%lukB"
 			" mlocked:%lukB"
@@ -332,6 +333,11 @@ static void show_free_areas(unsigned int filter, nodemask_t *nodemask, int max_z
 			K(zone_page_state(zone, NR_ZONE_INACTIVE_FILE)),
 			K(zone_page_state(zone, NR_ZONE_UNEVICTABLE)),
 			K(zone_page_state(zone, NR_ZONE_WRITE_PENDING)),
+#if IS_ENABLED(CONFIG_ZSMALLOC)
+			K(zone_page_state(zone, NR_ZSPAGES)),
+#else
+			0UL,
+#endif
 			K(zone->present_pages),
 			K(zone_managed_pages(zone)),
 			K(zone_page_state(zone, NR_MLOCK)),

---
base-commit: b320789d6883cc00ac78ce83bccbfe7ed58afcf0
change-id: 20250902-show_mem_zspages-d090ea0bd1d4

Best regards,
-- 
Thadeu Lima de Souza Cascardo <cascardo@igalia.com>