memcg: implement mem_cgroup_css_from_page() (ad7fa852) · Commits · 戴 / test

Implement mem_cgroup_css_from_page() which returns the cgroup_subsys_state of the memcg associated with a given page on the default hierarchy. This will be used by cgroup writeback support. This function assumes that page->mem_cgroup association doesn't change until the page is released, which is true on the default hierarchy as long as replace_page_cache_page() is not used. As the only user of replace_page_cache_page() is FUSE which won't support cgroup writeback for the time being, this works for now, and replace_page_cache_page() will soon be updated so that the invariant actually holds. Note that the RCU protected page->mem_cgroup access is consistent with other usages across memcg but ultimately incorrect. These unlocked accesses are missing required barriers. page->mem_cgroup should be made an RCU pointer and updated and accessed using RCU operations. v4: Instead of triggering WARN, return the root css on the traditional hierarchies. This makes the function a lot easier to deal with especially as there's no light way to synchronize against hierarchy rebinding. v3: s/mem_cgroup_migrate()/mem_cgroup_css_from_page()/ v2: Trigger WARN if the function is used on the traditional hierarchies and add comment about the assumed invariant. Signed-off-by:

Tejun Heo <tj@kernel.org> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Michal Hocko <mhocko@suse.cz> Signed-off-by:

Jens Axboe <axboe@fb.com>

include/linux/memcontrol.h

+1 −0

Original line number	Diff line number	Diff line
		@@ -115,6 +115,7 @@ static inline bool mm_match_cgroup(struct mm_struct *mm,
		}

		extern struct cgroup_subsys_state mem_cgroup_css(struct mem_cgroup memcg);
		extern struct cgroup_subsys_state mem_cgroup_css_from_page(struct page page);

		struct mem_cgroup mem_cgroup_iter(struct mem_cgroup ,
		struct mem_cgroup *,

mm/memcontrol.c

+33 −0

Original line number	Diff line number	Diff line
		@@ -598,6 +598,39 @@ struct cgroup_subsys_state mem_cgroup_css(struct mem_cgroup memcg)
		return &memcg->css;
		}

		/**
		* mem_cgroup_css_from_page - css of the memcg associated with a page
		* @page: page of interest
		*
		* If memcg is bound to the default hierarchy, css of the memcg associated
		* with @page is returned. The returned css remains associated with @page
		* until it is released.
		*
		* If memcg is bound to a traditional hierarchy, the css of root_mem_cgroup
		* is returned.
		*
		* XXX: The above description of behavior on the default hierarchy isn't
		* strictly true yet as replace_page_cache_page() can modify the
		* association before @page is released even on the default hierarchy;
		* however, the current and planned usages don't mix the the two functions
		* and replace_page_cache_page() will soon be updated to make the invariant
		* actually true.
		*/
		struct cgroup_subsys_state mem_cgroup_css_from_page(struct page page)
		{
		struct mem_cgroup *memcg;

		rcu_read_lock();

		memcg = page->mem_cgroup;

		if (!memcg \|\| !cgroup_on_dfl(memcg->css.cgroup))
		memcg = root_mem_cgroup;

		rcu_read_unlock();
		return &memcg->css;
		}

		static struct mem_cgroup_per_zone *
		mem_cgroup_page_zoneinfo(struct mem_cgroup memcg, struct page page)
		{

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