On Fri, Oct 2, 2020 at 10:26 AM Roman Gushchin <guro@xxxxxx> wrote: > > Currently there are many open-coded reads of the page->mem_cgroup > pointer, as well as a couple of read helpers, which are barely used. > > It creates an obstacle on a way to reuse some bits of the pointer > for storing additional bits of information. In fact, we already do > this for slab pages, where the last bit indicates that a pointer has > an attached vector of objcg pointers instead of a regular memcg > pointer. > > This commits uses 2 existing helpers and introduces a new helper to > converts all read sides to calls of these helpers: > struct mem_cgroup *page_memcg(struct page *page); > struct mem_cgroup *page_memcg_rcu(struct page *page); > struct mem_cgroup *page_memcg_check(struct page *page); > > page_memcg_check() is intended to be used in cases when the page > can be a slab page and have a memcg pointer pointing at objcg vector. > It does check the lowest bit, and if set, returns NULL. > page_memcg() contains a VM_BUG_ON_PAGE() check for the page not > being a slab page. > > To make sure nobody uses a direct access, struct page's > mem_cgroup/obj_cgroups is converted to unsigned long memcg_data. > > Signed-off-by: Roman Gushchin <guro@xxxxxx> > Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx> Reviewed-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
