Messages in this thread |  | | Date | Thu, 1 Oct 2020 13:27:13 -0400 | From | Johannes Weiner <> | Subject | Re: [PATCH v4 4/4] mm: convert page kmemcg type to a page memcg flag |
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On Thu, Oct 01, 2020 at 07:00:36PM +0200, Michal Koutný wrote: > Hi. > > On Wed, Sep 30, 2020 at 05:27:10PM -0700, Roman Gushchin <guro@fb.com> wrote: > > @@ -369,8 +371,12 @@ enum page_memcg_data_flags { > > */ > > static inline struct mem_cgroup *page_memcg(struct page *page) > > { > > + unsigned long memcg_data = page->memcg_data; > > + > > VM_BUG_ON_PAGE(PageSlab(page), page); > > - return (struct mem_cgroup *)page->memcg_data; > > + VM_BUG_ON_PAGE(memcg_data & MEMCG_DATA_OBJCGS, page); > > + > > + return (struct mem_cgroup *)(memcg_data & ~MEMCG_DATA_FLAGS_MASK); > > } > Shouldn't this change go also into page_memcg_rcu()? (I don't think the > current single user (workingset_activation() would pass a non-slab > kernel page but for consistency sake.)
+1
> Alternatively, I'm thinking why (in its single use) is there > page_memcg_rcu() a separate function to page_memcg() (cross memcg page > migration?).
It goes back to commit 55779ec759ccc3c12b917b3712a7716e1140c652.
The activation code is the only path where page migration is not excluded. Because unlike with page state statistics, we don't really mind a race when counting an activation event.
I do think there is a bug, though: mem_cgroup_move_account() should use WRITE_ONCE() on page->mem_cgroup.
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