Re: [RFC][PATCH 8/10] memcg: clean up charge/uncharge anon

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

On Tue, 29 Sep 2009 12:03:48 +0900
Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote:

> Just to make sure.
> 
> > > Maybe there is something I don't understand..
> > > IIUC, when page_remove_rmap() is called by do_wp_page(),
> > > there must be pte(s) which points to the page and a pte is guarded by
> > > page table lock. So, I think page_mapcount() > 0 before calling page_remove_rmap()
> > > because there must be a valid pte, at least.
> > > 
> > > Can this scenario happen ?
> > I think so. I intended to mention this case :)
> > I'm sorry for my vague explanation.
> > 
> > > ==
> > >     Thread A.                                      Thread B.
> > > 
> > >     do_wp_page()                                 do_swap_page()
> > >        PageAnon(oldpage)                         
> > >          lock_page()                             lock_page()=> wait.
> > >          reuse = false.
> > >          unlock_page()                           get lock.      
> > >        do copy-on-write
> > >        pte_same() == true
> > >          page_remove_rmap(oldpage) (mapcount goes to -1)
> > >                                                  page_set_anon_rmap() (new anon rmap again)
> > > ==
> > > Then, oldpage's mapcount goes down to 0 and up to 1 immediately.
> > > 
> I meant "process" not "thread".
Okay ;)

> I think this cannot happen in the case of threads, because these page_remove_rmap()
> and page_set_anon_rmap() are called under pte lock(they share the pte).
> 
Anyway, I'll fix this patch.
But Balbir ask me to post batched_charge/uncharge first, this clean up series
will be postponed.

I think..

  1. post softlimit fixes.
  2. batched uncharge/charge
  3. post some fixes from this set.

I personally want to reorder all functions but it makes diff (between versions)
too big. So, I think I should avoid big reorganization.
I'll go moderate way.
Hmm..but I'll do move percpu/perzone functions below definitions of structs.

Thanks,
-Kame

> 
> Thanks,
> Daisuke Nishimura.
> 

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