On Mon, Mar 1, 2021 at 7:03 PM Muchun Song [off-list ref] wrote:

On Tue, Mar 2, 2021 at 2:11 AM Shakeel Butt [off-list ref] wrote:

quoted

On Sun, Feb 28, 2021 at 10:25 PM Muchun Song [off-list ref] wrote:

quoted

We want to reuse the obj_cgroup APIs to reparent the kmem pages when
the memcg offlined. If we do this, we should store an object cgroup
pointer to page->memcg_data for the kmem pages.

Finally, page->memcg_data can 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.

Currently we always get the memcg associated with a page via page_memcg
or page_memcg_rcu. page_memcg_check is special, it has to be used in
cases when it's not known if a page has an associated memory cgroup
pointer or an object cgroups vector. Because the page->memcg_data of
the kmem page is not pointing to a memory cgroup in the later patch,
the page_memcg and page_memcg_rcu cannot be applicable for the kmem
pages. In this patch, we introduce page_memcg_kmem to get the memcg
associated with the kmem pages. And make page_memcg and page_memcg_rcu
no longer apply to the kmem pages.

In the end, there are 4 helpers to get the memcg associated with a
page. The usage is as follows.

  1) Get the memory cgroup associated with a non-kmem page (e.g. the LRU
     pages).

     - page_memcg()
     - page_memcg_rcu()

Can you rename these to page_memcg_lru[_rcu] to make them explicitly
for LRU pages?

Yes. Will do. Thanks.

Please follow Johannes' suggestion regarding page_memcg_kmem() and
then no need to rename these.