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Date:   Fri, 8 Mar 2019 16:15:46 +0000
From:   Christopher Lameter <cl@linux.com>
To:     Tycho Andersen <tycho@tycho.ws>
cc:     "Tobin C. Harding" <tobin@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Pekka Enberg <penberg@cs.helsinki.fi>,
        Matthew Wilcox <willy@infradead.org>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Subject: Re: [RFC 02/15] slub: Add isolate() and migrate() methods
In-Reply-To: <20190308152820.GB373@cisco>
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References: <20190308041426.16654-1-tobin@kernel.org> <20190308041426.16654-3-tobin@kernel.org> <20190308152820.GB373@cisco>
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On Fri, 8 Mar 2019, Tycho Andersen wrote:

> On Fri, Mar 08, 2019 at 03:14:13PM +1100, Tobin C. Harding wrote:
> > diff --git a/mm/slab_common.c b/mm/slab_common.c
> > index f9d89c1b5977..754acdb292e4 100644
> > --- a/mm/slab_common.c
> > +++ b/mm/slab_common.c
> > @@ -298,6 +298,10 @@ int slab_unmergeable(struct kmem_cache *s)
> >  	if (!is_root_cache(s))
> >  		return 1;
> >
> > +	/*
> > +	 * s->isolate and s->migrate imply s->ctor so no need to
> > +	 * check them explicitly.
> > +	 */
>
> Shouldn't this implication go the other way, i.e.
>     s->ctor => s->isolate & s->migrate

A cache can have a constructor but the object may not be movable (I.e.
currently dentries and inodes).