linux-kernel - Re: Low overhead patches for the memory cgroup controller (v5)

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Tue, 23 Jun 2009 09:01:16 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	balbir@...ux.vnet.ibm.com, kamezawa.hiroyuki@...fujitsu.com,
	nishimura@....nes.nec.co.jp, lizf@...fujitsu.com,
	menage@...gle.com, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: Low overhead patches for the memory cgroup controller (v5)

On Mon, 22 Jun 2009 15:43:43 -0700
Andrew Morton <akpm@...ux-foundation.org> wrote:

> On Mon, 15 Jun 2009 10:09:00 +0530
> Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:
> 
> >
> > ...
> > 
> > This patch changes the memory cgroup and removes the overhead associated
> > with accounting all pages in the root cgroup. As a side-effect, we can
> > no longer set a memory hard limit in the root cgroup.
> > 
> > A new flag to track whether the page has been accounted or not
> > has been added as well. Flags are now set atomically for page_cgroup,
> > pcg_default_flags is now obsolete and removed.
> > 
> > ...
> >
> > @@ -1114,9 +1121,22 @@ static void __mem_cgroup_commit_charge(struct mem_cgroup *mem,
> >  		css_put(&mem->css);
> >  		return;
> >  	}
> > +
> >  	pc->mem_cgroup = mem;
> >  	smp_wmb();
> > -	pc->flags = pcg_default_flags[ctype];
> > +	switch (ctype) {
> > +	case MEM_CGROUP_CHARGE_TYPE_CACHE:
> > +	case MEM_CGROUP_CHARGE_TYPE_SHMEM:
> > +		SetPageCgroupCache(pc);
> > +		SetPageCgroupUsed(pc);
> > +		break;
> > +	case MEM_CGROUP_CHARGE_TYPE_MAPPED:
> > +		ClearPageCgroupCache(pc);
> > +		SetPageCgroupUsed(pc);
> > +		break;
> > +	default:
> > +		break;
> > +	}
> 
> Do we still need the smp_wmb()?
> 
> It's hard to say, because we forgot to document it :(
> 
Sorry for lack of documentation.

pc->mem_cgroup should be visible before SetPageCgroupUsed(). Othrewise,
A routine believes USED bit will see bad pc->mem_cgroup.

I'd like to  add a comment later (againt new mmotm.)

Thanks,
-Kame




--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/