From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail138.messagelabs.com (mail138.messagelabs.com [216.82.249.35]) by kanga.kvack.org (Postfix) with SMTP id A15316B005C for ; Thu, 15 Jan 2009 00:16:10 -0500 (EST) Received: from m3.gw.fujitsu.co.jp ([10.0.50.73]) by fgwmail7.fujitsu.co.jp (Fujitsu Gateway) with ESMTP id n0F5G8eG003385 for (envelope-from kamezawa.hiroyu@jp.fujitsu.com); Thu, 15 Jan 2009 14:16:08 +0900 Received: from smail (m3 [127.0.0.1]) by outgoing.m3.gw.fujitsu.co.jp (Postfix) with ESMTP id CCA6045DD7F for ; Thu, 15 Jan 2009 14:16:07 +0900 (JST) Received: from s3.gw.fujitsu.co.jp (s3.gw.fujitsu.co.jp [10.0.50.93]) by m3.gw.fujitsu.co.jp (Postfix) with ESMTP id 40FD645DD78 for ; Thu, 15 Jan 2009 14:16:07 +0900 (JST) Received: from s3.gw.fujitsu.co.jp (localhost.localdomain [127.0.0.1]) by s3.gw.fujitsu.co.jp (Postfix) with ESMTP id 258791DB803C for ; Thu, 15 Jan 2009 14:16:07 +0900 (JST) Received: from m107.s.css.fujitsu.com (m107.s.css.fujitsu.com [10.249.87.107]) by s3.gw.fujitsu.co.jp (Postfix) with ESMTP id A6C4D1DB8040 for ; Thu, 15 Jan 2009 14:16:03 +0900 (JST) Date: Thu, 15 Jan 2009 14:14:58 +0900 From: KAMEZAWA Hiroyuki Subject: Re: [RFC][PATCH 5/4] memcg: don't call res_counter_uncharge when obsolete Message-Id: <20090115141458.818b4e9a.kamezawa.hiroyu@jp.fujitsu.com> In-Reply-To: <20090115133814.a52460fa.nishimura@mxp.nes.nec.co.jp> References: <20090113184533.6ffd2af9.nishimura@mxp.nes.nec.co.jp> <20090114175121.275ecd59.nishimura@mxp.nes.nec.co.jp> <7602a77a9fc6b1e8757468048fde749a.squirrel@webmail-b.css.fujitsu.com> <20090115100330.37d89d3d.nishimura@mxp.nes.nec.co.jp> <20090115110044.3a863af8.kamezawa.hiroyu@jp.fujitsu.com> <20090115111420.8559bdb3.nishimura@mxp.nes.nec.co.jp> <20090115133814.a52460fa.nishimura@mxp.nes.nec.co.jp> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Daisuke Nishimura Cc: LKML , linux-mm , Andrew Morton , Balbir Singh , Pavel Emelyanov , Li Zefan , Paul Menage List-ID: On Thu, 15 Jan 2009 13:38:14 +0900 Daisuke Nishimura wrote: > On Thu, 15 Jan 2009 11:14:20 +0900, Daisuke Nishimura 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 believe get/put at create/destroy is enough now.. Let's try and see what happens. 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 > > > > > > > > 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 > > > 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 > > > > 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 > > --- > > 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); > > } > > } > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. 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