Hello KAMEZAWA-san,

On Tue, Jan 18, 2011 at 11:40:49AM +0900, KAMEZAWA Hiroyuki wrote:

+void mem_cgroup_split_huge_fixup(struct page *head, struct page *tail)
+{
+	struct page_cgroup *head_pc = lookup_page_cgroup(head);
+	struct page_cgroup *tail_pc = lookup_page_cgroup(tail);
+	unsigned long flags;
+
+	/*
+	 * We have no races witch charge/uncharge but will have races with
+	 * page state accounting.
+	 */
+	move_lock_page_cgroup(head_pc, &flags);
+
+	tail_pc->mem_cgroup = head_pc->mem_cgroup;
+	smp_wmb(); /* see __commit_charge() */

I thought the barriers were needed because charging does not hold the
lru lock.  But here we do, and all the 'lockless' read-sides do so as
well.  Am I missing something or can this barrier be removed?

	Hannes

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