mm: remove references to folio in split_page_memcg()

We know that the passed in page is not part of a folio (it's a plain page
allocated with GFP_ACCOUNT), so we should get rid of the misleading
references to folios.

Introduce page_objcg() and page_set_objcg() helpers to make things more
clear.

Link: https://lkml.kernel.org/r/20250314133617.138071-4-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Acked-by: Roman Gushchin <roman.gushchin@linux.dev>
Cc: David Hildenbrand <david@redhat.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index fa7a3a1b710a42c7efae532a44efa53d28d72542..d95b1f4216ac49527554db5a2ab136b0935465e4 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2677,6 +2677,23 @@ out:
        return ret;
 }
 
+static struct obj_cgroup *page_objcg(const struct page *page)
+{
+       unsigned long memcg_data = page->memcg_data;
+
+       if (mem_cgroup_disabled() || !memcg_data)
+               return NULL;
+
+       VM_BUG_ON_PAGE((memcg_data & OBJEXTS_FLAGS_MASK) != MEMCG_DATA_KMEM,
+                       page);
+       return (struct obj_cgroup *)(memcg_data - MEMCG_DATA_KMEM);
+}
+
+static void page_set_objcg(struct page *page, const struct obj_cgroup *objcg)
+{
+       page->memcg_data = (unsigned long)objcg | MEMCG_DATA_KMEM;
+}
+
 /**
  * __memcg_kmem_charge_page: charge a kmem page to the current memory cgroup
  * @page: page to charge
@@ -2695,8 +2712,7 @@ int __memcg_kmem_charge_page(struct page *page, gfp_t gfp, int order)
                ret = obj_cgroup_charge_pages(objcg, gfp, 1 << order);
                if (!ret) {
                        obj_cgroup_get(objcg);
-                       page->memcg_data = (unsigned long)objcg |
-                               MEMCG_DATA_KMEM;
+                       page_set_objcg(page, objcg);
                        return 0;
                }
        }
@@ -3069,18 +3085,18 @@ void __memcg_slab_free_hook(struct kmem_cache *s, struct slab *slab,
  * The objcg is only set on the first page, so transfer it to all the
  * other pages.
  */
-void split_page_memcg(struct page *first, unsigned order)
+void split_page_memcg(struct page *page, unsigned order)
 {
-       struct folio *folio = page_folio(first);
+       struct obj_cgroup *objcg = page_objcg(page);
        unsigned int i, nr = 1 << order;
 
-       if (mem_cgroup_disabled() || !folio_memcg_charged(folio))
+       if (!objcg)
                return;
 
        for (i = 1; i < nr; i++)
-               folio_page(folio, i)->memcg_data = folio->memcg_data;
+               page_set_objcg(&page[i], objcg);
 
-       obj_cgroup_get_many(__folio_objcg(folio), nr - 1);
+       obj_cgroup_get_many(objcg, nr - 1);
 }
 
 void folio_split_memcg_refs(struct folio *folio, unsigned old_order,