Messages in this thread Patch in this message | | | Date | Thu, 15 Jan 2009 17:23:36 +0900 | From | KAMEZAWA Hiroyuki <> | Subject | Re: [RFC][PATCH] memcg: get/put parents at create/free |
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On Thu, 15 Jan 2009 17:13:15 +0900 Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote:
> From: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> > > mem_cgroup_get ensures that the memcg that has been got can be accessed > even after the directory has been removed, but it doesn't ensure that parents > of it can be accessed: parents might have been freed already by rmdir. > > This causes a bug in case of use_hierarchy==1, because res_counter_uncharge > climb up the tree. > > This patch tries to fix this probrem by getting the parent at create, and > putting it at freeing. > > Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Seems very simple and promissive. But one nitpick
> --- > mm/memcontrol.c | 29 ++++++++++++++++++++++++++++- > 1 files changed, 28 insertions(+), 1 deletions(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index fb62b43..a80ba68 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 void mem_cgroup_get_parent(struct mem_cgroup *mem); > +static void mem_cgroup_put_parent(struct mem_cgroup *mem); > > static void mem_cgroup_charge_statistics(struct mem_cgroup *mem, > struct page_cgroup *pc, > @@ -2185,10 +2187,34 @@ 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)) { > + mem_cgroup_put_parent(mem); > __mem_cgroup_free(mem); > + } > +}
Here, parent is freed before children is freed. Then,
== if (atomic_dec_and_test(&mem->refcnt)) { struct mem_cgroup *parent = parent_mem_cgroup(mem); __mem_cgroup_free(mem); mem_cgroup_put(parent); } ==
Is maybe usual way.
-Kame
> + > +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); > } > > +static void mem_cgroup_put_parent(struct mem_cgroup *mem) > +{ > + struct mem_cgroup *parent = parent_mem_cgroup(mem); > + > + if (parent) > + mem_cgroup_put(parent); > +} > > #ifdef CONFIG_CGROUP_MEM_RES_CTLR_SWAP > static void __init enable_swap_cgroup(void) > @@ -2237,6 +2263,7 @@ 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); >
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