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Date: Mon, 7 Dec 2015 08:59:25 -0600 (CST)
From: Christoph Lameter <cl@linux.com>
Subject: Re: [RFC PATCH 2/2] slab: implement bulk free in SLAB allocator
In-Reply-To: <20151207122549.109e82db@redhat.com>
Message-ID: <alpine.DEB.2.20.1512070858140.8762@east.gentwo.org>
References: <20151203155600.3589.86568.stgit@firesoul> <20151203155736.3589.67424.stgit@firesoul> <alpine.DEB.2.20.1512041111180.21819@east.gentwo.org> <20151207122549.109e82db@redhat.com>
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To: Jesper Dangaard Brouer <brouer@redhat.com>
Cc: linux-mm@kvack.org, Vladimir Davydov <vdavydov@virtuozzo.com>, Joonsoo Kim <iamjoonsoo.kim@lge.com>, Linus Torvalds <torvalds@linux-foundation.org>, Andrew Morton <akpm@linux-foundation.org>

On Mon, 7 Dec 2015, Jesper Dangaard Brouer wrote:

> > s?
>
> The "s" comes from the slub.c code uses "struct kmem_cache *s" everywhere.

Ok then use it. Why is there an orig_s here.

> > > +
> > > +	local_irq_disable();
> > > +	for (i = 0; i < size; i++) {
> > > +		void *objp = p[i];
> > > +
> > > +		s = cache_from_obj(orig_s, objp);
> >
> > Does this support freeing objects from a set of different caches?
>
> This is for supporting memcg (CONFIG_MEMCG_KMEM).
>
> Quoting from commit 033745189b1b ("slub: add missing kmem cgroup
> support to kmem_cache_free_bulk"):
>
>    Incoming bulk free objects can belong to different kmem cgroups, and
>    object free call can happen at a later point outside memcg context.  Thus,
>    we need to keep the orig kmem_cache, to correctly verify if a memcg object
>    match against its "root_cache" (s->memcg_params.root_cache).

Where is that verification? This looks like SLAB would support freeing
objects from different caches.

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