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authorTejun Heo <tj@kernel.org>2015-05-27 20:00:02 -0400
committerJens Axboe <axboe@fb.com>2015-06-02 08:33:34 -0600
commitad7fa852d3d2816d68a138ebc5bc8967aeb7fd86 (patch)
tree11c52a605228523e1f0009192ae4f16ed83b5aeb /mm
parent1d933cf096e3aea15f1aec8297657b7a846fab63 (diff)
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memcg: implement mem_cgroup_css_from_page()
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>
Diffstat (limited to 'mm')
-rw-r--r--mm/memcontrol.c33
1 files changed, 33 insertions, 0 deletions
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index b22a92b37480..5c270a03729c 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -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)
{