On Mon, Jul 09, 2012 at 01:22:54PM +0800, Sha Zhengju wrote:
> On 07/09/2012 12:18 PM, Kamezawa Hiroyuki wrote:
> >(2012/07/09 13:14), Fengguang Wu wrote:
> >>On Mon, Jul 09, 2012 at 11:36:11AM +0800, Sha Zhengju wrote:
> >>>On 07/08/2012 10:53 PM, Fengguang Wu wrote:
> >>>>>@@ -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..
> >>
> >>>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...
Yeah, it helps to add some brief comment on the locking rule in
account_page_*().
Thanks,
Fengguang
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxx. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>