[PATCH 3/3] fs, mm: account buffer_head to kmemcg

Shakeel Butt
2018-06-19T05:13:56Z

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.

Signed-off-by: Shakeel Butt <shakeelb@google.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Greg Thelen <gthelen@google.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Andrew Morton <akpm@linux-foundation.org>
---
fs/buffer.c | 14 +++++++++++++-
include/linux/memcontrol.h | 7 +++++++
mm/memcontrol.c | 21 +++++++++++++++++++++
3 files changed, 41 insertions(+), 1 deletion(-)

diff --git a/fs/buffer.c b/fs/buffer.c
index 8194e3049fc5..26389b7a3cab 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -815,10 +815,17 @@ struct buffer_head *alloc_page_buffers(struct page *page, unsigned long size,
struct buffer_head *bh, *head;
gfp_t gfp = GFP_NOFS;
long offset;
+ struct mem_cgroup *old_memcg;
+ struct mem_cgroup *memcg = get_mem_cgroup_from_page(page);

if (retry)
gfp |= __GFP_NOFAIL;

+ if (memcg) {
+ gfp |= __GFP_ACCOUNT;
+ old_memcg = memalloc_memcg_save(memcg);
+ }
+
head = NULL;
offset = PAGE_SIZE;
while ((offset -= size) >= 0) {
@@ -835,6 +842,11 @@ struct buffer_head *alloc_page_buffers(struct page *page, unsigned long size,
/* Link the buffer to its page */
set_bh_page(bh, page, offset);
}
+out:
+ if (memcg) {
+ memalloc_memcg_restore(old_memcg);
+#ifdef CONFIG_MEMCG
+ css_put(&memcg->css);
+#endif
+ }
return head;
/*
* In case anything failed, we just free everything we got.
@@ -848,7 +860,7 @@ struct buffer_head *alloc_page_buffers(struct page *page, unsigned long size,
} while (head);
}

- return NULL;
+ goto out;
}
EXPORT_SYMBOL_GPL(alloc_page_buffers);

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 6c857be8a9b7..d53609978eb7 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -380,6 +380,8 @@ struct mem_cgroup *mem_cgroup_from_task(struct task_struct *p);

struct mem_cgroup *get_mem_cgroup_from_mm(struct mm_struct *mm);

+struct mem_cgroup *get_mem_cgroup_from_page(struct page *page);
+
static inline
struct mem_cgroup *mem_cgroup_from_css(struct cgroup_subsys_state *css){
return css ? container_of(css, struct mem_cgroup, css) : NULL;
@@ -864,6 +866,11 @@ static inline struct mem_cgroup *get_mem_cgroup_from_mm(struct mm_struct *mm)
return NULL;
}

+static inline struct mem_cgroup *get_mem_cgroup_from_page(struct page *page)
+{
+ return NULL;
+}
+
static inline void mem_cgroup_put(struct mem_cgroup *memcg)
{
}
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index c481e661e051..f9a9a79117b9 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -712,6 +712,27 @@ struct mem_cgroup *get_mem_cgroup_from_mm(struct mm_struct *mm)
return memcg;
}

+/**
+ * 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
+ * NULL is returned.
+ */
+struct mem_cgroup *get_mem_cgroup_from_page(struct page *page)
+{
+ struct mem_cgroup *memcg = page->mem_cgroup;
+
+ if (mem_cgroup_disabled() || !memcg)
+ return NULL;
+
+ rcu_read_lock();
+ if (!css_tryget_online(&memcg->css))
+ memcg = NULL;
+ rcu_read_unlock();
+ return memcg;
+}
+
static __always_inline struct mem_cgroup *get_mem_cgroup(
struct mem_cgroup *memcg, struct mm_struct *mm)
{
--
2.18.0.rc1.244.gcf134e6275-goog