>From 26bab580abfc441c841c1983469b8b86f5a8ef5c Mon Sep 17 00:00:00 2001
From: Tejun Heo <tj@xxxxxxxxxx>
Date: Wed, 27 May 2015 12:08:29 -0400
Implement mem_cgroup_css_from_page() which returns the
cgroup_subsys_state of the memcg associated with a given page. 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 mem_cgroup_migrate() is not used. As the only user of
mem_cgroup_migrate() is FUSE which won't support cgroup writeback for
the time being, this works for now, and mem_cgroup_migrate() will soon
be updated so that the invariant actually holds.
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@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxx>
---
Added WARN and comments. No functional change. git branches updated
accordingly.
Thanks.
include/linux/memcontrol.h | 1 +
mm/memcontrol.c | 31 +++++++++++++++++++++++++++++++
2 files changed, 32 insertions(+)
diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 294498f..637ef62 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -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 *,
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index b22a92b..c76b85c 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -598,6 +598,37 @@ 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
+ *
+ * This function is guaranteed to return a valid cgroup_subsys_state and
+ * the returned css remains associated with @page until it is released.
+ *
+ * This can only be used on the default hierarchy as @page's memcg
+ * association may change on the traditional hierarchies. Use
+ * try_get_mem_cgroup_from_page() instead on the traditional hierarchies.
+ *
+ * XXX: The above comment isn't true yet as mem_cgroup_migrate() 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 mem_cgroup_migrate() will soon be updated to
+ * make the invariant actually true.
+ */
+struct cgroup_subsys_state *mem_cgroup_css_from_page(struct page *page)
+{
+ struct cgroup_subsys_state *css;
+
+ if (page->mem_cgroup)
+ css = &page->mem_cgroup->css;
+ else
+ css = &root_mem_cgroup->css;
+
+ WARN_ON_ONCE(!cgroup_on_dfl(css->cgroup));
+
+ return css;
+}
+
static struct mem_cgroup_per_zone *
mem_cgroup_page_zoneinfo(struct mem_cgroup *memcg, struct page *page)
{
--
2.4.0
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