fs: buffer: use raw page_memcg() on locked page
alloc_page_buffers() currently uses get_mem_cgroup_from_page() for
charging the buffers to the page owner, which does an rcu-protected
page->memcg lookup and acquires a reference. But buffer allocation has
the page lock held throughout, which pins the page to the memcg and
thereby the memcg - neither rcu nor holding an extra reference during the
allocation are necessary. Use a raw page_memcg() instead.
This was the last user of get_mem_cgroup_from_page(), delete it.
Link: https://lkml.kernel.org/r/20210209190126.97842-1-hannes@cmpxchg.org
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Reported-by: Muchun Song <songmuchun@bytedance.com>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Acked-by: Roman Gushchin <guro@fb.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/buffer.c b/fs/buffer.c
index f1c3a5b..0cb7ffd 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -847,7 +847,8 @@ struct buffer_head *alloc_page_buffers(struct page *page, unsigned long size,
if (retry)
gfp |= __GFP_NOFAIL;
- memcg = get_mem_cgroup_from_page(page);
+ /* The page lock pins the memcg */
+ memcg = page_memcg(page);
old_memcg = set_active_memcg(memcg);
head = NULL;
@@ -868,7 +869,6 @@ struct buffer_head *alloc_page_buffers(struct page *page, unsigned long size,
}
out:
set_active_memcg(old_memcg);
- mem_cgroup_put(memcg);
return head;
/*
* In case anything failed, we just free everything we got.