Messages in this thread | | | Date | Thu, 15 Jan 2009 15:39:31 +0900 | From | KAMEZAWA Hiroyuki <> | Subject | Re: [RFC][PATCH 5/4] memcg: don't call res_counter_uncharge when obsolete |
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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 ? > "don't free parent's css_id until all chilredn are freed" is necessary for my CSS ID. I'll rebase my patch on to yours.
thanks, -Kame
> > Thanks, > Daisuke Nishimura. > > > > > > So, adding css_tryget() around problematic code can be a fix. > > > > > -- > > > > > mem = swap_cgroup_record(); > > > > > if (css_tryget(&mem->css)) { > > > > > res_counter_uncharge(&mem->memsw, PAZE_SIZE); > > > > > css_put(&mem->css) > > > > > } > > > > > -- > > > > > I like css_tryget() rather than mem_cgroup_obsolete(). > > > > I agree. > > > > The updated version is attached. > > > > > > > > > > > > Thanks, > > > > Daisuke nishimura. > > > > > > > > > To be honest, I'd like to remove memcg special stuff when I can. > > > > > > > > > > Thanks, > > > > > -Kame > > > > > > > > > === > > > > 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. > > > > > > > > Check if the memcg is obsolete by css_tryget, and don't call > > > > res_counter_uncharge when obsole. > > > > > > > > Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> > > > seems nice loock. > > > > > > > > > > --- > > > > mm/memcontrol.c | 15 ++++++++++++--- > > > > 1 files changed, 12 insertions(+), 3 deletions(-) > > > > > > > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > > > > index fb62b43..4e3b100 100644 > > > > --- a/mm/memcontrol.c > > > > +++ b/mm/memcontrol.c > > > > @@ -1182,7 +1182,10 @@ int mem_cgroup_cache_charge(struct page *page, struct mm_struct *mm, > > > > /* avoid double counting */ > > > > mem = swap_cgroup_record(ent, NULL); > > > > if (mem) { > > > > - res_counter_uncharge(&mem->memsw, PAGE_SIZE); > > > > + if (!css_tryget(&mem->css)) { > > > > + res_counter_uncharge(&mem->memsw, PAGE_SIZE); > > > > + css_put(&mem->css); > > > > + } > > > > mem_cgroup_put(mem); > > > > } > > > > } > > > > > > I think css_tryget() returns "ture" at success.... > > > > > > So, > > > == > > > if (mem && css_tryget(&mem->css)) > > > res_counter.... > > > > > > is correct. > > > > > > -Kame > > > > > Ooops! you are right. > > Sorry for my silly mistake.. > > > > "mem" is checked beforehand, so I think css_tryget would be enough. > > I'm now testing the attached one. > > > > > > 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. > > > > Check if the memcg is obsolete by css_tryget, and don't call > > res_counter_uncharge when obsole. > > > > Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> > > --- > > mm/memcontrol.c | 15 ++++++++++++--- > > 1 files changed, 12 insertions(+), 3 deletions(-) > > > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > > index fb62b43..b9d5271 100644 > > --- a/mm/memcontrol.c > > +++ b/mm/memcontrol.c > > @@ -1182,7 +1182,10 @@ int mem_cgroup_cache_charge(struct page *page, struct mm_struct *mm, > > /* avoid double counting */ > > mem = swap_cgroup_record(ent, NULL); > > if (mem) { > > - res_counter_uncharge(&mem->memsw, PAGE_SIZE); > > + if (css_tryget(&mem->css)) { > > + res_counter_uncharge(&mem->memsw, PAGE_SIZE); > > + css_put(&mem->css); > > + } > > mem_cgroup_put(mem); > > } > > } > > @@ -1252,7 +1255,10 @@ void mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *ptr) > > struct mem_cgroup *memcg; > > memcg = swap_cgroup_record(ent, NULL); > > if (memcg) { > > - res_counter_uncharge(&memcg->memsw, PAGE_SIZE); > > + if (css_tryget(&memcg->css)) { > > + res_counter_uncharge(&memcg->memsw, PAGE_SIZE); > > + css_put(&memcg->css); > > + } > > mem_cgroup_put(memcg); > > } > > > > @@ -1397,7 +1403,10 @@ void mem_cgroup_uncharge_swap(swp_entry_t ent) > > > > memcg = swap_cgroup_record(ent, NULL); > > if (memcg) { > > - res_counter_uncharge(&memcg->memsw, PAGE_SIZE); > > + if (css_tryget(&memcg->css)) { > > + res_counter_uncharge(&memcg->memsw, PAGE_SIZE); > > + css_put(&memcg->css); > > + } > > mem_cgroup_put(memcg); > > } > > } >
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