Re: [PATCH(v2) -mmotm 2/2] memcg move charge of shmem at task migration

[Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>]

On Tue, 30 Mar 2010 10:30:50 +0530, Balbir Singh <balbir@linux.vnet.ibm.com> wrote:
> * KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> [2010-03-30 13:51:59]:
> 
> > On Tue, 30 Mar 2010 13:06:48 +0900
> > Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote:
> > 
> > > On Tue, 30 Mar 2010 12:11:19 +0900, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> > > > On Tue, 30 Mar 2010 11:49:03 +0900
> > > > Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote:
> > > > 
> > > > > On Tue, 30 Mar 2010 11:23:01 +0900, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> > > > > > SHARED mapped file cache is not moved by patch [1/2] ???
> > > > > > It sounds strange.
> > > > > > 
> > > > > hmm, I'm sorry I'm not so good at user applications, but is it usual to use
> > > > > VM_SHARED file caches(!tmpfs) ?
> > > > > And is it better for us to move them only when page_mapcount() == 1 ?
> > > > > 
> > > > 
> > > > Considering shared library which has only one user, moving MAP_SHARED makes sense.
> > > > Unfortunately, there are people who creates their own shared library just for
> > > > their private dlopen() etc. (shared library for private use...)
> > > > 
> > > > So, I think moving MAP_SHARED files makes sense.
> > > > 
> 
> IIRC, the libraries are loaded with MAP_PRIVATE and MAP_SHARED is not
> set.
> 
Thank you for your information.

> > > Thank you for your explanations.
> > > I'll update my patches to allow to move MAP_SHARED(but page_mapcount() == 1)
> > > file caches, and resend.
> > > 
> > 
> > Hmm, considering again...current summary is following...right ?
> > 
> >  - If page is an anon, it's not moved if page_mapcount() > 2.
> >  - If page is a page cache, it's not moved if page_mapcount() > 2.
> >  - If page is a shmem, it's not moved regardless of mapcount.
> >  - If pte is swap, it's not moved refcnt > 2.
> > 
Right.

> > I think following is straightforward and simple.
> > 
> >  - If page is an anon or swap of anon, it's not moved if referer > 2. 
> 
> What is referer in this context? The cgroup refering to the page?
> 
> >    (i.e. inherited from it's parent)
> >  - If page is file,shmem or swap of shmem, it's moved regardless of referer.
> >    But pages only under "from" memcg can be moved.
> > 
> > I doubt adding too much speciality to shmem is not good.
> >
> 
> Yep, I tend to agree, but I need to take a closer look again at the
> patches. 
> 
I agree it would be more simple. I selected the current policy because
I was not sure whether we should move file caches(!tmpfs) with mapcount > 1,
and, IMHO, shared memory and file caches are different for users.
But it's O.K. for me to change current policy.


Thanks,
Daisuke Nishimura.

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