On Wed, Dec 01, 2021 at 07:15:00PM +0100, Vlastimil Babka wrote:
> page->memcg_data is used with MEMCG_DATA_OBJCGS flag only for slab pages
> so convert all the related infrastructure to struct slab.
>
> To avoid include cycles, move the inline definitions of slab_objcgs() and
> slab_objcgs_check() from memcontrol.h to mm/slab.h.
>
> This is not just mechanistic changing of types and names. Now in
> mem_cgroup_from_obj() we use PageSlab flag to decide if we interpret the page
> as slab, instead of relying on MEMCG_DATA_OBJCGS bit checked in
> page_objcgs_check() (now slab_objcgs_check()). Similarly in
> memcg_slab_free_hook() where we can encounter kmalloc_large() pages (here the
> PageSlab flag check is implied by virt_to_slab()).
Yup, this is great.
> @@ -2865,24 +2865,31 @@ int memcg_alloc_page_obj_cgroups(struct page *page, struct kmem_cache *s,
> */
> struct mem_cgroup *mem_cgroup_from_obj(void *p)
> {
> - struct page *page;
> + struct folio *folio;
>
> if (mem_cgroup_disabled())
> return NULL;
>
> - page = virt_to_head_page(p);
> + folio = virt_to_folio(p);
>
> /*
> * Slab objects are accounted individually, not per-page.
> * Memcg membership data for each individual object is saved in
> * the page->obj_cgroups.
> */
> - if (page_objcgs_check(page)) {
> + if (folio_test_slab(folio)) {
> + struct obj_cgroup **objcgs;
> struct obj_cgroup *objcg;
> + struct slab *slab;
> unsigned int off;
>
> - off = obj_to_index(page->slab_cache, page_slab(page), p);
> - objcg = page_objcgs(page)[off];
> + slab = folio_slab(folio);
> + objcgs = slab_objcgs_check(slab);
AFAICS the change to the _check() variant was accidental.
folio_test_slab() makes sure it's a slab page, so the legit options
for memcg_data are NULL or |MEMCG_DATA_OBJCGS; using slab_objcgs()
here would include the proper asserts, like page_objcgs() used to.
