On Wed, Sep 30, 2020 at 05:27:10PM -0700, Roman Gushchin wrote: > PageKmemcg flag is currently defined as a page type (like buddy, > offline, table and guard). Semantically it means that the page > was accounted as a kernel memory by the page allocator and has > to be uncharged on the release. > > As a side effect of defining the flag as a page type, the accounted > page can't be mapped to userspace (look at page_has_type() and > comments above). In particular, this blocks the accounting of > vmalloc-backed memory used by some bpf maps, because these maps > do map the memory to userspace. > > One option is to fix it by complicating the access to page->mapcount, > which provides some free bits for page->page_type. > > But it's way better to move this flag into page->memcg_data flags. > Indeed, the flag makes no sense without enabled memory cgroups > and memory cgroup pointer set in particular. > > This commit replaces PageKmemcg() and __SetPageKmemcg() with > PageMemcgKmem() and an open-coded OR operation setting the memcg > pointer with the MEMCG_DATA_KMEM bit. __ClearPageKmemcg() can be > simple deleted, as the whole memcg_data is zeroed at once. > > As a bonus, on !CONFIG_MEMCG build the PageMemcgKmem() check will > be compiled out. > > Signed-off-by: Roman Gushchin <guro@xxxxxx> Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
