memcg: add memcg sanity checks at allocating and freeing pages

Add checks at allocating or freeing a page whether the page is used (iow,
charged) from the view point of memcg.

This check may be useful in debugging a problem and we did similar checks
before the commit 52d4b9ac(memcg: allocate all page_cgroup at boot).

This patch adds some overheads at allocating or freeing memory, so it's
enabled only when CONFIG_DEBUG_VM is enabled.

Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: Minchan Kim <minchan.kim@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 46 insertions, 0 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 3a2d54bdf076..0356cb6c9504 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3046,6 +3046,52 @@ int mem_cgroup_shmem_charge_fallback(struct page *page,
         return ret;
 }
 
+#ifdef CONFIG_DEBUG_VM
+static struct page_cgroup *lookup_page_cgroup_used(struct page *page)
+{
+        struct page_cgroup *pc;
+
+        pc = lookup_page_cgroup(page);
+        if (likely(pc) && PageCgroupUsed(pc))
+                return pc;
+        return NULL;
+}
+
+bool mem_cgroup_bad_page_check(struct page *page)
+{
+        if (mem_cgroup_disabled())
+                return false;
+
+        return lookup_page_cgroup_used(page) != NULL;
+}
+
+void mem_cgroup_print_bad_page(struct page *page)
+{
+        struct page_cgroup *pc;
+
+        pc = lookup_page_cgroup_used(page);
+        if (pc) {
+                int ret = -1;
+                char *path;
+
+                printk(KERN_ALERT "pc:%p pc->flags:%lx pc->mem_cgroup:%p",
+                       pc, pc->flags, pc->mem_cgroup);
+
+                path = kmalloc(PATH_MAX, GFP_KERNEL);
+                if (path) {
+                        rcu_read_lock();
+                        ret = cgroup_path(pc->mem_cgroup->css.cgroup,
+                                                        path, PATH_MAX);
+                        rcu_read_unlock();
+                }
+
+                printk(KERN_CONT "(%s)\n",
+                                (ret < 0) ? "cannot get the path" : path);
+                kfree(path);
+        }
+}
+#endif
+
 static DEFINE_MUTEX(set_limit_mutex);
 
 static int mem_cgroup_resize_limit(struct mem_cgroup *memcg,