On 07/09/2012 12:18 PM, Kamezawa Hiroyuki wrote:

(2012/07/09 13:14), Fengguang Wu wrote:

quoted

On Mon, Jul 09, 2012 at 11:36:11AM +0800, Sha Zhengju wrote:

quoted

On 07/08/2012 10:53 PM, Fengguang Wu wrote:

quoted

quoted

@@ -2245,7 +2252,10 @@ int test_set_page_writeback(struct page *page)
  {
      struct address_space *mapping = page_mapping(page);
      int ret;
+    bool locked;
+    unsigned long flags;

+    mem_cgroup_begin_update_page_stat(page,&locked,&flags);
      if (mapping) {
          struct backing_dev_info *bdi = mapping->backing_dev_info;
          unsigned long flags;

@@ -2272,6 +2282,8 @@ int test_set_page_writeback(struct page *page)
      }
      if (!ret)
          account_page_writeback(page);
+
+    mem_cgroup_end_update_page_stat(page,&locked,&flags);
      return ret;

  }

Where is the MEM_CGROUP_STAT_FILE_WRITEBACK increased?

It's in account_page_writeback().

  void account_page_writeback(struct page *page)
  {
+    mem_cgroup_inc_page_stat(page, MEM_CGROUP_STAT_FILE_WRITEBACK);
      inc_zone_page_state(page, NR_WRITEBACK);
  }

I didn't find that chunk, perhaps it's lost due to rebase..

quoted

There isn't a unified interface to dec/inc writeback accounting, so
I just follow that.
Maybe we can rework account_page_writeback() to also account
dec in?

The current seperate inc/dec paths are fine. It sounds like
over-engineering if going any further.

I'm a bit worried about some 3rd party kernel module to call
account_page_writeback() without 
mem_cgroup_begin/end_update_page_stat().
Will that lead to serious locking issues, or merely inaccurate
accounting?

Ah, Hm. Maybe it's better to add some debug check in
 mem_cgroup_update_page_stat(). rcu_read_lock_held() or some.

This also apply to account_page_dirtied()... But as an "range" lock, I 
think it's common
in current kernel: just as set_page_dirty(), the caller should call it 
under the page lock
(in most cases) and it's his responsibility to guarantee correctness. I 
can add some
comments or debug check as reminding but I think i can only do so...


Thanks,
Sha