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...
Thanks,
Sha
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