fs, mm: account buffer_head to kmemcg

The buffer_head can consume a significant amount of system memory and is
directly related to the amount of page cache.  In our production
environment we have observed that a lot of machines are spending a
significant amount of memory as buffer_head and can not be left as
system memory overhead.

Charging buffer_head is not as simple as adding __GFP_ACCOUNT to the
allocation.  The buffer_heads can be allocated in a memcg different from
the memcg of the page for which buffer_heads are being allocated.  One
concrete example is memory reclaim.  The reclaim can trigger I/O of
pages of any memcg on the system.  So, the right way to charge
buffer_head is to extract the memcg from the page for which buffer_heads
are being allocated and then use targeted memcg charging API.

[shakeelb@google.com: use __GFP_ACCOUNT for directed memcg charging]
  Link: http://lkml.kernel.org/r/20180702220208.213380-1-shakeelb@google.com
Link: http://lkml.kernel.org/r/20180627191250.209150-3-shakeelb@google.com
Signed-off-by: Shakeel Butt <shakeelb@google.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Amir Goldstein <amir73il@gmail.com>
Cc: Greg Thelen <gthelen@google.com>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 22 insertions, 0 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index bf9cf738c836..c071af193986 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -714,6 +714,28 @@ struct mem_cgroup *get_mem_cgroup_from_mm(struct mm_struct *mm)
 EXPORT_SYMBOL(get_mem_cgroup_from_mm);
 
 /**
+ * get_mem_cgroup_from_page: Obtain a reference on given page's memcg.
+ * @page: page from which memcg should be extracted.
+ *
+ * Obtain a reference on page->memcg and returns it if successful. Otherwise
+ * root_mem_cgroup is returned.
+ */
+struct mem_cgroup *get_mem_cgroup_from_page(struct page *page)
+{
+	struct mem_cgroup *memcg = page->mem_cgroup;
+
+	if (mem_cgroup_disabled())
+		return NULL;
+
+	rcu_read_lock();
+	if (!memcg || !css_tryget_online(&memcg->css))
+		memcg = root_mem_cgroup;
+	rcu_read_unlock();
+	return memcg;
+}
+EXPORT_SYMBOL(get_mem_cgroup_from_page);
+
+/**
  * If current->active_memcg is non-NULL, do not fallback to current->mm->memcg.
  */
 static __always_inline struct mem_cgroup *get_mem_cgroup_from_current(void)