linux-kernel - Re: [RFC 02/15] slub: Add isolate() and migrate() methods

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Message-ID: <010001695e16cdef-9831bf56-3075-4f0e-8c25-5d60103cb95f-000000@email.amazonses.com>
Date:   Fri, 8 Mar 2019 16:15:46 +0000
From:   Christopher Lameter <cl@...ux.com>
To:     Tycho Andersen <tycho@...ho.ws>
cc:     "Tobin C. Harding" <tobin@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Pekka Enberg <penberg@...helsinki.fi>,
        Matthew Wilcox <willy@...radead.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC 02/15] slub: Add isolate() and migrate() methods

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).