Let's count the number of CMA pages per zone and print them in
/proc/zoneinfo.

Having access to the total number of CMA pages per zone is helpful for
debugging purposes to know where exactly the CMA pages ended up, and to
figure out how many pages of a zone might behave differently, even after
some of these pages might already have been allocated.

As one example, CMA pages part of a kernel zone cannot be used for
ordinary kernel allocations but instead behave more like ZONE_MOVABLE.

For now, we are only able to get the global nr+free cma pages from
/proc/meminfo and the free cma pages per zone from /proc/zoneinfo.

Example after this patch when booting a 6 GiB QEMU VM with
"hugetlb_cma=2G":
  # cat /proc/zoneinfo | grep cma
          cma      0
        nr_free_cma  0
          cma      0
        nr_free_cma  0
          cma      524288
        nr_free_cma  493016
          cma      0
          cma      0
  # cat /proc/meminfo | grep Cma
  CmaTotal:        2097152 kB
  CmaFree:         1972064 kB

Note: We print even without CONFIG_CMA, just like "nr_free_cma"; this way,
      one can be sure when spotting "cma 0", that there are definetly no
      CMA pages located in a zone.

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Thomas Gleixner <redacted>
Cc: "Peter Zijlstra (Intel)" <peterz@infradead.org>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Wei Yang <redacted>
Cc: David Rientjes <rientjes@google.com>
Cc: linux-api@vger.kernel.org
Signed-off-by: David Hildenbrand <redacted>
---

The third time is the charm.

v2 -> v3:
- Print even without CONFIG_CMA. Use zone_cma_pages().
- Adjust patch description
- Dropped Oscar's RB due to the changes

v1 -> v2:
- Print/track only with CONFIG_CMA
- Extend patch description

---
 include/linux/mmzone.h | 15 +++++++++++++++
 mm/page_alloc.c        |  1 +
 mm/vmstat.c            |  6 ++++--
 3 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index ae588b2f87ef..caafd5e37080 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h

@@ -503,6 +503,9 @@ struct zone {
 	 * bootmem allocator):
 	 *	managed_pages = present_pages - reserved_pages;
 	 *
+	 * cma pages is present pages that are assigned for CMA use
+	 * (MIGRATE_CMA).
+	 *
 	 * So present_pages may be used by memory hotplug or memory power
 	 * management logic to figure out unmanaged pages by checking
 	 * (present_pages - managed_pages). And managed_pages should be used

@@ -527,6 +530,9 @@ struct zone {
 	atomic_long_t		managed_pages;
 	unsigned long		spanned_pages;
 	unsigned long		present_pages;
+#ifdef CONFIG_CMA
+	unsigned long		cma_pages;
+#endif
 
 	const char		*name;
 

@@ -624,6 +630,15 @@ static inline unsigned long zone_managed_pages(struct zone *zone)
 	return (unsigned long)atomic_long_read(&zone->managed_pages);
 }
 
+static inline unsigned long zone_cma_pages(struct zone *zone)
+{
+#ifdef CONFIG_CMA
+	return zone->cma_pages;
+#else
+	return 0;
+#endif
+}
+
 static inline unsigned long zone_end_pfn(const struct zone *zone)
 {
 	return zone->zone_start_pfn + zone->spanned_pages;

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index b031a5ae0bd5..9a82375bbcb2 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c

@@ -2168,6 +2168,7 @@ void __init init_cma_reserved_pageblock(struct page *page)
 	}
 
 	adjust_managed_page_count(page, pageblock_nr_pages);
+	page_zone(page)->cma_pages += pageblock_nr_pages;
 }
 #endif
 

diff --git a/mm/vmstat.c b/mm/vmstat.c
index 7758486097f9..b2537852d498 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c

@@ -1642,14 +1642,16 @@ static void zoneinfo_show_print(struct seq_file *m, pg_data_t *pgdat,
 		   "\n        high     %lu"
 		   "\n        spanned  %lu"
 		   "\n        present  %lu"
-		   "\n        managed  %lu",
+		   "\n        managed  %lu"
+		   "\n        cma      %lu",
 		   zone_page_state(zone, NR_FREE_PAGES),
 		   min_wmark_pages(zone),
 		   low_wmark_pages(zone),
 		   high_wmark_pages(zone),
 		   zone->spanned_pages,
 		   zone->present_pages,
-		   zone_managed_pages(zone));
+		   zone_managed_pages(zone),
+		   zone_cma_pages(zone));
 
 	seq_printf(m,
 		   "\n        protection: (%ld",

-- 
2.29.2