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charset=us-ascii Content-Disposition: inline In-Reply-To: <20200127173453.2089565-17-guro@fb.com> X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, Jan 27, 2020 at 09:34:41AM -0800, Roman Gushchin wrote: > Allocate and release memory to store obj_cgroup pointers for each > non-root slab page. Reuse page->mem_cgroup pointer to store a pointer > to the allocated space. > > To distinguish between obj_cgroups and memcg pointers in case > when it's not obvious which one is used (as in page_cgroup_ino()), > let's always set the lowest bit in the obj_cgroup case. > > Signed-off-by: Roman Gushchin > --- > include/linux/mm.h | 25 ++++++++++++++++++-- > include/linux/mm_types.h | 5 +++- > mm/memcontrol.c | 5 ++-- > mm/slab.c | 3 ++- > mm/slab.h | 51 +++++++++++++++++++++++++++++++++++++++- > mm/slub.c | 2 +- > 6 files changed, 83 insertions(+), 8 deletions(-) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index 080f8ac8bfb7..65224becc4ca 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -1264,12 +1264,33 @@ static inline void set_page_links(struct page *page, enum zone_type zone, > #ifdef CONFIG_MEMCG > static inline struct mem_cgroup *page_memcg(struct page *page) > { > - return page->mem_cgroup; > + struct mem_cgroup *memcg = page->mem_cgroup; > + > + /* > + * The lowest bit set means that memcg isn't a valid memcg pointer, > + * but a obj_cgroups pointer. In this case the page is shared and > + * isn't charged to any specific memory cgroup. Return NULL. > + */ > + if ((unsigned long) memcg & 0x1UL) > + memcg = NULL; > + > + return memcg; That should really WARN instead of silently returning NULL. Which callsite optimistically asks a page's cgroup when it has no idea whether that page is actually a userpage or not? > static inline struct mem_cgroup *page_memcg_rcu(struct page *page) > { > + struct mem_cgroup *memcg = READ_ONCE(page->mem_cgroup); > + > WARN_ON_ONCE(!rcu_read_lock_held()); > - return READ_ONCE(page->mem_cgroup); > + > + /* > + * The lowest bit set means that memcg isn't a valid memcg pointer, > + * but a obj_cgroups pointer. In this case the page is shared and > + * isn't charged to any specific memory cgroup. Return NULL. > + */ > + if ((unsigned long) memcg & 0x1UL) > + memcg = NULL; > + > + return memcg; Same here. > } > #else > static inline struct mem_cgroup *page_memcg(struct page *page) > diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h > index 270aa8fd2800..5102f00f3336 100644 > --- a/include/linux/mm_types.h > +++ b/include/linux/mm_types.h > @@ -198,7 +198,10 @@ struct page { > atomic_t _refcount; > > #ifdef CONFIG_MEMCG > - struct mem_cgroup *mem_cgroup; > + union { > + struct mem_cgroup *mem_cgroup; > + struct obj_cgroup **obj_cgroups; > + }; Since you need the casts in both cases anyway, it's safer (and simpler) to do unsigned long mem_cgroup; to prevent accidental direct derefs in future code. Otherwise, this patch looks good to me!