Re: [PATCH -mmotm 7/8] memcg: move charges of anonymous swap

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

On Thu, 4 Feb 2010 14:09:42 +0900
Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote:

> On Wed, 3 Feb 2010 19:31:27 -0800, Andrew Morton <akpm@linux-foundation.org> wrote:
> > On Mon, 21 Dec 2009 14:38:16 +0900 Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote:
> > 
> > > This patch is another core part of this move-charge-at-task-migration feature.
> > > It enables moving charges of anonymous swaps.
> > > 
> > > To move the charge of swap, we need to exchange swap_cgroup's record.
> > > 
> > > In current implementation, swap_cgroup's record is protected by:
> > > 
> > >   - page lock: if the entry is on swap cache.
> > >   - swap_lock: if the entry is not on swap cache.
> > > 
> > > This works well in usual swap-in/out activity.
> > > 
> > > But this behavior make the feature of moving swap charge check many conditions
> > > to exchange swap_cgroup's record safely.
> > > 
> > > So I changed modification of swap_cgroup's recored(swap_cgroup_record())
> > > to use xchg, and define a new function to cmpxchg swap_cgroup's record.
> > > 
> > > This patch also enables moving charge of non pte_present but not uncharged swap
> > > caches, which can be exist on swap-out path, by getting the target pages via
> > > find_get_page() as do_mincore() does.
> > > 
> > >
> > > ...
> > >
> > > +		else if (is_swap_pte(ptent)) {
> > 
> > is_swap_pte() isn't implemented for CONFIG_MMU=n, so the build breaks.
> Ah, you're right. I'm sorry I don't have any evironment to test !CONFIG_MMU.
> 
> Using #ifdef like below would be the simplest fix(SWAP is depend on MMU),
> but hmm, #ifdef is ugly.
> 
> I'll prepare another fix.
> 
Hmm..is there any user of memcg in !CONFIG_MMU environment ?
Maybe memcg can be used for controling amount of file cache (per cgroup)..
but..

I think memcg should depends on CONIFG_MMU.

How do you think ?

Thanks,
-Kame

> ===
> From: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
> 
> build fix in !CONFIG_MMU case.
> 
> Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
> ---
>  mm/memcontrol.c |    2 ++
>  1 files changed, 2 insertions(+), 0 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 953b18b..85b48cb 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -3635,6 +3635,7 @@ static int is_target_pte_for_mc(struct vm_area_struct *vma,
>  					&mc.to->move_charge_at_immigrate);
>  
>  	if (!pte_present(ptent)) {
> +#ifdef CONFIG_SWAP
>  		/* TODO: handle swap of shmes/tmpfs */
>  		if (pte_none(ptent) || pte_file(ptent))
>  			return 0;
> @@ -3644,6 +3645,7 @@ static int is_target_pte_for_mc(struct vm_area_struct *vma,
>  				return 0;
>  			usage_count = mem_cgroup_count_swap_user(ent, &page);
>  		}
> +#endif
>  	} else {
>  		page = vm_normal_page(vma, addr, ptent);
>  		if (!page || !page_mapped(page))
> -- 
> 1.6.4
> 
> 

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