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    SubjectRe: [PATCH 3/9] blkio-cgroup-v9: The new page_cgroup framework
    On Wed, 22 Jul 2009 14:07:22 +0530
    Balbir Singh <balbir@linux.vnet.ibm.com> wrote:

    > * Ryo Tsuruta <ryov@valinux.co.jp> [2009-07-22 17:28:43]:
    >
    > > KAMEZAWA Hiroyuki <kamezawa.hiroyu@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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