[Devel] Re: [PATCH 2/4] swapcgroup: add member to swap_info_struct for cgroup

[KAMEZAWA Hiroyuki]

On Thu, 22 May 2008 17:46:54 +0900
Daisuke Nishimura <nishimura at mxp.nes.nec.co.jp> wrote:

> > ==
> > #ifdef CONFIG_CGROUP_SWAP_RES_CTR
> >   void  swap_cgroup_init_memcg(p, memcg)
> >   {
> >     do something.
> >   }
> > #else
> >    void  swap_cgroup_init_memcg(p, memcg)
> >   {
> >   }
> > #endif
> > ==
> > 
> I think swap_cgroup_init_memcg should return old value
> of p->memcg, and I would like to name it swap_cgroup_clear_memcg,
> because it is called by sys_swapoff, so "clear" rather than "init"
> would be better.
> 
> How about something like this?
> 
> struct mem_cgroup **swap_cgroup_clear_memcg(p, memcg)
> {
> 	struct mem_cgroup **mem;
> 
> 	mem = p->memcg;
> 	p->memcg = NULL;
> 
> 	return mem;
> }
> 
> and at sys_swapoff():
> 
> struct mem_cgroup **memcg;
>  :
> memcg = swap_cgroup_clear_memcg(p, memcg);
>  :
> if (memcg)
> 	vfree(memcg);
> 
seems good.


> >> +#ifdef CONFIG_CGROUP_SWAP_RES_CTLR
> >> +		p->memcg = vmalloc(maxpages * sizeof(struct mem_cgroup *));
> >> +		if (!p->memcg) {
> >> +			error = -ENOMEM;
> >> +			goto bad_swap;
> >> +		}
> >> +		memset(p->memcg, 0, maxpages * sizeof(struct mem_cgroup *));
> >> +#endif
> > void alloc_swap_ctlr_memcg(p)
> > 
> OK.
> I'll implement swap_cgroup_alloc_memcg.
> 
> > But this implies swapon will fail at memory shortage. Is it good ?
> > 
> Hum.
> Would it be better to just disabling this feature?
> 
I have no good idea. IMHO, adding printk() to show 'fatal status of
not-enough-memory-for-vmalloc' will be first step.

I believe vmalloc() tend not to fail on 64bit machine, but on i386,
vmalloc area is not enough.

Thanks,
-Kame

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