[PATCH -mm 4/6] memcg: interface to charge the right cgroup of asynchronous i/o activity

[Andrea Righi]

Implement get_cgroup_from_page() / put_cgroup_from_page() in the cgroup memory
controller to retrieve the owner of a page during writes in submit_bio()
processed asynchronously by kernel threads (i.e. pdflush).

Note: right now this is no more than a hack to keep the things simpler; in
perspective this functionality could/should be provided by bio-cgroup [1],
instead of directly use the memcg page-tracking functionality.

[1] http://people.valinux.co.jp/~ryov/bio-cgroup/

Signed-off-by: Andrea Righi <righi.andrea@xxxxxxxxx>
---
 include/linux/memcontrol.h |    3 +++
 mm/memcontrol.c            |   26 ++++++++++++++++++++++++++
 2 files changed, 29 insertions(+), 0 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index ee1b2fc..92dfd40 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -50,6 +50,9 @@ int task_in_mem_cgroup(struct task_struct *task, const struct mem_cgroup *mem);
 
 extern struct mem_cgroup *mem_cgroup_from_task(struct task_struct *p);
 
+extern struct cgroup *get_cgroup_from_page(struct page *page);
+extern void put_cgroup_from_page(struct page *page);
+
 #define mm_match_cgroup(mm, cgroup)	\
 	((cgroup) == mem_cgroup_from_task((mm)->owner))
 
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 2979d22..5321b8b 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -279,6 +279,32 @@ static void unlock_page_cgroup(struct page *page)
 	bit_spin_unlock(PAGE_CGROUP_LOCK_BIT, &page->page_cgroup);
 }
 
+struct cgroup *get_cgroup_from_page(struct page *page)
+{
+	struct page_cgroup *pc;
+	struct cgroup *cgrp = NULL;
+
+	lock_page_cgroup(page);
+	pc = page_get_page_cgroup(page);
+	if (pc) {
+		css_get(&pc->mem_cgroup->css);
+		cgrp = pc->mem_cgroup->css.cgroup;
+	}
+	unlock_page_cgroup(page);
+	return cgrp;
+}
+
+void put_cgroup_from_page(struct page *page)
+{
+	struct page_cgroup *pc;
+
+	lock_page_cgroup(page);
+	pc = page_get_page_cgroup(page);
+	if (pc)
+		css_put(&pc->mem_cgroup->css);
+	unlock_page_cgroup(page);
+}
+
 static void __mem_cgroup_remove_list(struct mem_cgroup_per_zone *mz,
 			struct page_cgroup *pc)
 {
-- 
1.5.4.3

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