On Fri, Mar 19, 2021 at 9:39 AM Muchun Song <songmuchun@xxxxxxxxxxxxx> wrote: > > Since Roman series "The new cgroup slab memory controller" applied. All > slab objects are charged via the new APIs of obj_cgroup. The new APIs > introduce a struct obj_cgroup to charge slab objects. It prevents > long-living objects from pinning the original memory cgroup in the memory. > But there are still some corner objects (e.g. allocations larger than > order-1 page on SLUB) which are not charged via the new APIs. Those > objects (include the pages which are allocated from buddy allocator > directly) are charged as kmem pages which still hold a reference to > the memory cgroup. > > We want to reuse the obj_cgroup APIs to charge the kmem pages. > If we do that, we should store an object cgroup pointer to > page->memcg_data for the kmem pages. > > Finally, page->memcg_data will have 3 different meanings. > > 1) For the slab pages, page->memcg_data points to an object cgroups > vector. > > 2) For the kmem pages (exclude the slab pages), page->memcg_data > points to an object cgroup. > > 3) For the user pages (e.g. the LRU pages), page->memcg_data points > to a memory cgroup. > > We do not change the behavior of page_memcg() and page_memcg_rcu(). > They are also suitable for LRU pages and kmem pages. Why? > > Because memory allocations pinning memcgs for a long time - it exists > at a larger scale and is causing recurring problems in the real world: > page cache doesn't get reclaimed for a long time, or is used by the > second, third, fourth, ... instance of the same job that was restarted > into a new cgroup every time. Unreclaimable dying cgroups pile up, > waste memory, and make page reclaim very inefficient. > > We can convert LRU pages and most other raw memcg pins to the objcg > direction to fix this problem, and then the page->memcg will always > point to an object cgroup pointer. At that time, LRU pages and kmem > pages will be treated the same. The implementation of page_memcg() > will remove the kmem page check. > > This patch aims to charge the kmem pages by using the new APIs of > obj_cgroup. Finally, the page->memcg_data of the kmem page points to > an object cgroup. We can use the __page_objcg() to get the object > cgroup associated with a kmem page. Or we can use page_memcg() > to get the memory cgroup associated with a kmem page, but caller must > ensure that the returned memcg won't be released (e.g. acquire the > rcu_read_lock or css_set_lock). > > Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx> > Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx> Reviewed-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
