linux-kernel - Re: [PATCH 1/2] gfp: add __GFP

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]

Message-ID: <20150506123541.GK14550@dhcp22.suse.cz>
Date:	Wed, 6 May 2015 14:35:41 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Vladimir Davydov <vdavydov@...allels.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Tejun Heo <tj@...nel.org>, Christoph Lameter <cl@...ux.com>,
	Pekka Enberg <penberg@...nel.org>,
	David Rientjes <rientjes@...gle.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Greg Thelen <gthelen@...gle.com>, linux-mm@...ck.org,
	cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] gfp: add __GFP_NOACCOUNT

On Wed 06-05-15 15:24:31, Vladimir Davydov wrote:
> On Wed, May 06, 2015 at 01:59:41PM +0200, Michal Hocko wrote:
> > On Tue 05-05-15 12:45:42, Vladimir Davydov wrote:
> > > Not all kmem allocations should be accounted to memcg. The following
> > > patch gives an example when accounting of a certain type of allocations
> > > to memcg can effectively result in a memory leak.
> > 
> > > This patch adds the __GFP_NOACCOUNT flag which if passed to kmalloc
> > > and friends will force the allocation to go through the root
> > > cgroup. It will be used by the next patch.
> > 
> > The name of the flag is way too generic. It is not clear that the
> > accounting is KMEMCG related. __GFP_NO_KMEMCG sounds better?
> > 
> > I was going to suggest doing per-cache rather than gfp flag and that
> > would actually work just fine for the kmemleak as it uses its own cache
> > already. But the ida_simple_get would be trickier because it doesn't use
> > any special cache and more over only one user seem to have a problem so
> > this doesn't sound like a good fit.
> 
> I don't think making this flag per-cache is an option either, but for
> another reason - it would not be possible to merge such a kmem cache
> with caches without this flag set. As a result, total memory pressure
> would increase, even for setups without kmem-active memory cgroups,
> which does not sound acceptable to me.

I am not sure I see the performance implications here because kmem
accounted memcgs would have their copy of the cache anyway, no?
Anyway, I guess it would be good to document these reasons in the
changelog.
 
> > So I do not object to opt-out for kmemcg accounting but I really think
> > the name should be changed.
> 
> I named it __GFP_NOACCOUNT to match with __GFP_NOTRACK, which is a very
> specific flag too (kmemcheck),  nevertheless it has a rather generic
> name.

__GFP_NOTRACK is a bad name IMHO as well. One has to go and check the
comment to see this is kmemleak related.

> Anyways, what else apart from memcg can account kmem so that we have to
> mention KMEMCG in the flag name explicitly?

NOACCOUNT doesn't imply kmem at all so it is not clear who is in charge
of the accounting. I do not insist on __GFP_NO_KMEMCG of course but
it sounds quite specific about its meaning and scope.
-- 
Michal Hocko
SUSE Labs
--
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/