Re: [PATCH -mmotm 3/4] memcg: dirty pages accounting and limiting infrastructure

[Andrea Righi <arighi@develer.com>]

On Fri, Mar 05, 2010 at 10:58:55AM +0900, KAMEZAWA Hiroyuki wrote:
> On Fri, 5 Mar 2010 10:12:34 +0900
> Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote:
> 
> > On Thu,  4 Mar 2010 11:40:14 +0100, Andrea Righi <arighi@develer.com> wrote:
> > > Infrastructure to account dirty pages per cgroup and add dirty limit
> > >  static int mem_cgroup_count_children_cb(struct mem_cgroup *mem, void *data)
> > >  {
> > >  	int *val = data;
> > > @@ -1275,34 +1423,70 @@ static void record_last_oom(struct mem_cgroup *mem)
> > >  }
> > >  
> > >  /*
> > > - * Currently used to update mapped file statistics, but the routine can be
> > > - * generalized to update other statistics as well.
> > > + * Generalized routine to update file cache's status for memcg.
> > > + *
> > > + * Before calling this, mapping->tree_lock should be held and preemption is
> > > + * disabled.  Then, it's guarnteed that the page is not uncharged while we
> > > + * access page_cgroup. We can make use of that.
> > >   */
> > IIUC, mapping->tree_lock is held with irq disabled, so I think "mapping->tree_lock
> > should be held with irq disabled" would be enouth.
> > And, as far as I can see, callers of this function have not ensured this yet in [4/4].
> > 
> > how about:
> > 
> > 	void mem_cgroup_update_stat_locked(...)
> > 	{
> > 		...
> > 	}
> > 
> > 	void mem_cgroup_update_stat_unlocked(mapping, ...)
> > 	{
> > 		spin_lock_irqsave(mapping->tree_lock, ...);
> > 		mem_cgroup_update_stat_locked();
> > 		spin_unlock_irqrestore(...);
> > 	}
> >
> Rather than tree_lock, lock_page_cgroup() can be used if tree_lock is not held.
> 
> 		lock_page_cgroup();
> 		mem_cgroup_update_stat_locked();
> 		unlock_page_cgroup();
> 
> Andrea-san, FILE_MAPPED is updated without treelock, at least. You can't depend
> on migration_lock about FILE_MAPPED.

Right. I'll consider this in the next version of the patch.

Thanks,
-Andrea