[dm-devel] Re: [PATCH 3/9] blkio-cgroup-v9: The new page_cgroup framework

[Ryo Tsuruta]

KAMEZAWA Hiroyuki <kamezawa.hiroyu at jp.fujitsu.com> wrote:
> > > > Index: linux-2.6.31-rc3/include/linux/page_cgroup.h
> > > > ===================================================================
> > > > --- linux-2.6.31-rc3.orig/include/linux/page_cgroup.h
> > > > +++ linux-2.6.31-rc3/include/linux/page_cgroup.h
> > > > @@ -1,7 +1,7 @@
> > > >  #ifndef __LINUX_PAGE_CGROUP_H
> > > >  #define __LINUX_PAGE_CGROUP_H
> > > > 
> > > > -#ifdef CONFIG_CGROUP_MEM_RES_CTLR
> > > > +#ifdef CONFIG_CGROUP_PAGE
> > > >  #include <linux/bit_spinlock.h>
> > > >  /*
> > > >   * Page Cgroup can be considered as an extended mem_map.
> > > > @@ -12,9 +12,11 @@
> > > >   */
> > > >  struct page_cgroup {
> > > >  	unsigned long flags;
> > > > -	struct mem_cgroup *mem_cgroup;
> > > >  	struct page *page;
> > > > +#ifdef CONFIG_CGROUP_MEM_RES_CTLR
> > > > +	struct mem_cgroup *mem_cgroup;
> > > >  	struct list_head lru;		/* per cgroup LRU list */
> > > > +#endif
> > > >  };
> > > 
> > > If CONFIG_CGROUP_MEM_RES_CTLR is not enabled and CGROUP_PAGE is
> > > (assuming that the depends on below is refactored), what would this
> > > change buy us? What is page_cgroup helping us track, the mem_cgroup is
> > > factored out, so we are interested in the flags only?
> > > 
> > plz remove CONFIG. This jsut makes code complicated.
> > or plz use your own infrastructure, not depends on page_cgroup.

Thanks for reviewing the patch.
Do you mean that remove only CONFIG_CGROUP_MEM_RES_CTR in struct
page_cgroup? Is it OK to define CONFIG_CGROUP_PAGE?

> BTW, you can't modify page_cgroup->flags bit without cmpxchg.
> Then, patch [5/9] is completely broken, now because new bit is used
> with atomic bit ops but without lock_page_cgroup(). (see mmotm)
> 
> Why struct page's flags bit can includes zone id etc...is just because
> it's initalized before using. Anyway, this is "flags" bit. If you want
> to modify multiple bit at once, plz use cmpxchg.
> Then, I buy patch [8/9] and just skip this patch.

O.K. I'll use cmpxchg.
 
> But, following is more straightforward. (and what you do is not different
> from this.)
> ==
> struct page {
> 	.....
> #ifdef CONFIG_BLOCKIO_CGROUP
> 	void *blockio_cgroup;
> #endif
> }
> ==

This increases the size of struct page. Could I get a consensus on
this approach?

Thanks,
Ryo Tsuruta

> Regards,
> -Kame
> 
>