On 12/14/21 15:43, Johannes Weiner wrote:
> 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.
Well spotted. On closer look, it's actually the same in
memcg_slab_free_hook() where I also added a folio_test_slab() as part of
virt_to_slab(). In fact it means page_objcgs_check() can be just deleted
instead of replaced by slab_objcgs_check(). Thanks!
