linux-kernel - Re: [PATCH v3 12/28] slab: pass memcg parameter to kmem_cache

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Date:	Tue, 29 May 2012 11:33:17 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Glauber Costa <glommer@...allels.com>
cc:	linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
	linux-mm@...ck.org, kamezawa.hiroyu@...fujitsu.com,
	Tejun Heo <tj@...nel.org>, Li Zefan <lizefan@...wei.com>,
	Greg Thelen <gthelen@...gle.com>,
	Suleiman Souhlal <suleiman@...gle.com>,
	Michal Hocko <mhocko@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>, devel@...nvz.org,
	David Rientjes <rientjes@...gle.com>,
	Pekka Enberg <penberg@...helsinki.fi>
Subject: Re: [PATCH v3 12/28] slab: pass memcg parameter to
 kmem_cache_create

On Tue, 29 May 2012, Glauber Costa wrote:

> > Ok this only duplicates the kmalloc arrays. Why not the others?
>
> It does duplicate the others.
>
> First it does a while look on the kmalloc caches, then a list_for_each_entry
> in the rest. You probably missed it.

There is no need to separately duplicate the kmalloc_caches. Those are
included on the cache_chain.

> > > @@ -2543,7 +2564,12 @@ kmem_cache_create (const char *name, size_t size,
> > > size_t align,
> > >   	cachep->ctor = ctor;
> > >   	cachep->name = name;
> > >
> > > +	if (g_cpucache_up>= FULL)
> > > +		mem_cgroup_register_cache(memcg, cachep);
> >
> > What happens if a cgroup was active during creation of slab xxy but
> > then a process running in a different cgroup uses that slab to allocate
> > memory? Is it charged to the first cgroup?
>
> I don't see this situation ever happening. kmem_cache_create, when called
> directly, will always create a global cache. It doesn't matter which cgroups
> are or aren't active at this time or any other. We create copies per-cgroup,
> but we create it lazily, when someone will touch it.

How do you detect that someone is touching it?
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