Messages in this thread Patch in this message | | | Date | Thu, 15 Jan 2009 17:13:15 +0900 | From | Daisuke Nishimura <> | Subject | Re: [RFC][PATCH] memcg: get/put parents at create/free |
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On Thu, 15 Jan 2009 16:54:53 +0900, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote: > On Thu, 15 Jan 2009 16:45:37 +0900 > Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote: > > > On Thu, 15 Jan 2009 13:38:14 +0900, Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote: > > > On Thu, 15 Jan 2009 11:14:20 +0900, Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote: > > > > > > > To handle the problem "parent may be obsolete", > > > > > > > > > > > > > > call mem_cgroup_get(parent) at create() > > > > > > > call mem_cgroup_put(parent) at freeing memcg. > > > > > > > (regardless of use_hierarchy.) > > > > > > > > > > > > > > is clearer way to go, I think. > > > > > > > > > > > > > > I wonder whether there is mis-accounting problem or not.. > > > > > > > > > > hmm, after more consideration, although this patch can prevent the BUG, > > > it can leak memsw accounting of parents because memsw of parents, which > > > have been incremented by charge, does not decremented. > > > > > > I'll try pet/put parent approach.. > > > Or any other good ideas ? > > > > > I attach a tryial patch. > > > > It has been working fine so far(for about 1 hour). > > > > Thanks, > > Daisuke Nishimura. > > === > > 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 parents at create, and > > putting them at freeing. > > > > Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> > > --- > > mm/memcontrol.c | 33 ++++++++++++++++++++++++++++++++- > > 1 files changed, 32 insertions(+), 1 deletions(-) > > > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > > index fb62b43..b4aed07 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_parents(struct mem_cgroup *mem); > > +static void mem_cgroup_put_parents(struct mem_cgroup *mem); > > > > static void mem_cgroup_charge_statistics(struct mem_cgroup *mem, > > struct page_cgroup *pc, > > @@ -2185,10 +2187,38 @@ 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_parents(mem); > > __mem_cgroup_free(mem); > > + } > > +} > > + > > +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_parents(struct mem_cgroup *mem) > > +{ > > + struct mem_cgroup *parent = parent_mem_cgroup(mem); > > + > > + while (parent) { > > + mem_cgroup_get(parent); > > + parent = parent_mem_cgroup(parent); > > + } > > } > > > > does we have to add refcnt to all ancestors ? > Ah, no need.
Just ensureing "a parent memcg is not freed while it has child memcg unfreed" would be enough, because a parent is a child of parent of the parent.
This is the updated version.
Thanks, Daisuke Nishimura. === 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> --- 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); + } +} + +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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