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author | Tejun Heo <tj@kernel.org> | 2015-05-27 20:00:02 -0400 |
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committer | Jens Axboe <axboe@fb.com> | 2015-06-02 08:33:34 -0600 |
commit | ad7fa852d3d2816d68a138ebc5bc8967aeb7fd86 (patch) | |
tree | 11c52a605228523e1f0009192ae4f16ed83b5aeb /mm | |
parent | 1d933cf096e3aea15f1aec8297657b7a846fab63 (diff) | |
download | linux-ad7fa852d3d2816d68a138ebc5bc8967aeb7fd86.tar.gz linux-ad7fa852d3d2816d68a138ebc5bc8967aeb7fd86.tar.bz2 linux-ad7fa852d3d2816d68a138ebc5bc8967aeb7fd86.zip |
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.c | 33 |
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) { |