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

[KAMEZAWA Hiroyuki]

On Wed, 22 Jul 2009 14:07:22 +0530
Balbir Singh <balbir at linux.vnet.ibm.com> wrote:

> * Ryo Tsuruta <ryov at valinux.co.jp> [2009-07-22 17:28:43]:
> 
> > 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?
> >
> 
> 
> This defeats the entire purpose of page_cgroup, IMHO. You need to add
> the cgroup pointer to page_cgroup or use css id's there.
>  
My point is
 - increasing size of struct page is verrry difficult.
 - increasing size of struct page_cgroup should be.
Any diffrence ?

Then, plz don't go this way without enough amounts of effort.
plz see my patch to reduce size struct page_cgroup, it's _a_ effort.

Thanks,
-Kame



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