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SubjectRe: [BUGFIX][PATCH] memcg: get/put parents at create/free
On Thu, 15 Jan 2009 18:12:43 -0800
Andrew Morton <akpm@linux-foundation.org> wrote:

> On Fri, 16 Jan 2009 10:50:09 +0900 Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote:
>
> > This version works well in my test.
> >
> > Andrew, please pick up this one.
> >
> > ===
> > From: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
> >
> > The lifetime of struct cgroup and struct mem_cgroup is different and
> > mem_cgroup has its own reference count for handling references from swap_cgroup.
> >
> > This causes strange problem that the parent mem_cgroup dies while
> > child mem_cgroup alive, and this problem causes a bug in case of use_hierarchy==1
> > because res_counter_uncharge climbs up the tree.
> >
> > This patch is for avoiding it by getting the parent at create, and
> > putting it at freeing.
> >
> > Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
> > Reviewed-by; KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> > ---
> > mm/memcontrol.c | 23 ++++++++++++++++++++++-
> > 1 files changed, 22 insertions(+), 1 deletions(-)
> >
> > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> > index fb62b43..45e1b51 100644
> > --- a/mm/memcontrol.c
> > +++ b/mm/memcontrol.c
> > @@ -202,6 +202,8 @@ pcg_default_flags[NR_CHARGE_TYPE] = {
> >
> > static void mem_cgroup_get(struct mem_cgroup *mem);
> > static void mem_cgroup_put(struct mem_cgroup *mem);
> > +static struct mem_cgroup *parent_mem_cgroup(struct mem_cgroup *mem);
> > +static void mem_cgroup_get_parent(struct mem_cgroup *mem);
> >
> > static void mem_cgroup_charge_statistics(struct mem_cgroup *mem,
> > struct page_cgroup *pc,
> > @@ -2185,10 +2187,28 @@ static void mem_cgroup_get(struct mem_cgroup *mem)
> >
> > static void mem_cgroup_put(struct mem_cgroup *mem)
> > {
> > - if (atomic_dec_and_test(&mem->refcnt))
> > + if (atomic_dec_and_test(&mem->refcnt)) {
> > + struct mem_cgroup *parent = parent_mem_cgroup(mem);
> > __mem_cgroup_free(mem);
> > + if (parent)
> > + mem_cgroup_put(parent);
> > + }
> > +}
> > +
> > +static struct mem_cgroup *parent_mem_cgroup(struct mem_cgroup *mem)
> > +{
> > + if (!mem->res.parent)
> > + return NULL;
> > + return mem_cgroup_from_res_counter(mem->res.parent, res);
> > }
> >
> > +static void mem_cgroup_get_parent(struct mem_cgroup *mem)
> > +{
> > + struct mem_cgroup *parent = parent_mem_cgroup(mem);
> > +
> > + if (parent)
> > + mem_cgroup_get(parent);
> > +}
> >
> > #ifdef CONFIG_CGROUP_MEM_RES_CTLR_SWAP
> > static void __init enable_swap_cgroup(void)
> > @@ -2237,6 +2257,7 @@ mem_cgroup_create(struct cgroup_subsys *ss, struct cgroup *cont)
> > if (parent)
> > mem->swappiness = get_swappiness(parent);
> > atomic_set(&mem->refcnt, 1);
> > + mem_cgroup_get_parent(mem);
> > return &mem->css;
> > free_out:
> > __mem_cgroup_free(mem);
>
> It seems strange that we add a little helper function for the get(),
> but open-code the put()?
>
Maybe I don't feel this as strange because I saw update history of this patch ;(
As you pointed out, I like open-code rather than helper here. Nishimura-san,
could you update ?

Thanks,
-Kame






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