linux-kernel - Re: SLUB: purpose of sysfs events on cache creation/removal

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Message-ID: <20200106115733.GH12699@dhcp22.suse.cz>
Date:   Mon, 6 Jan 2020 12:57:33 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Christopher Lameter <cl@...ux.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: SLUB: purpose of sysfs events on cache creation/removal

On Wed 04-12-19 18:32:24, Michal Hocko wrote:
> [Cc akpm - the email thread starts
> http://lkml.kernel.org/r/20191126121901.GE20912@dhcp22.suse.cz]

ping.

> On Wed 04-12-19 16:53:47, Cristopher Lameter wrote:
> > On Wed, 4 Dec 2019, Michal Hocko wrote:
> > 
> > > As I've said I believe it is quite risky. But if you as a maintainer
> > > believe this is the right thing to do I will not object. Care to send a
> > > patch?
> > 
> > From: Christoph Lameter <cl@...ux.com>
> > Subject: slub: Remove userspace notifier for cache add/remove
> > 
> > Kmem caches are internal kernel structures so it is strange that
> > userspace notifiers would be needed. And I am not aware of any use
> > of these notifiers. These notifiers may just exist because in the
> > initial slub release the sysfs code was copied from another
> > subsystem.
> > 
> > Signed-off-by: Christoph Lameter <cl@...ux.com>
> > 
> > Index: linux/mm/slub.c
> > ===================================================================
> > --- linux.orig/mm/slub.c	2019-12-02 15:13:23.948312925 +0000
> > +++ linux/mm/slub.c	2019-12-04 16:32:34.648550310 +0000
> > @@ -5632,19 +5632,6 @@ static struct kobj_type slab_ktype = {
> >  	.release = kmem_cache_release,
> >  };
> > 
> > -static int uevent_filter(struct kset *kset, struct kobject *kobj)
> > -{
> > -	struct kobj_type *ktype = get_ktype(kobj);
> > -
> > -	if (ktype == &slab_ktype)
> > -		return 1;
> > -	return 0;
> > -}
> > -
> > -static const struct kset_uevent_ops slab_uevent_ops = {
> > -	.filter = uevent_filter,
> > -};
> > -
> >  static struct kset *slab_kset;
> > 
> >  static inline struct kset *cache_kset(struct kmem_cache *s)
> > @@ -5712,7 +5699,6 @@ static void sysfs_slab_remove_workfn(str
> >  #ifdef CONFIG_MEMCG
> >  	kset_unregister(s->memcg_kset);
> >  #endif
> > -	kobject_uevent(&s->kobj, KOBJ_REMOVE);
> >  out:
> >  	kobject_put(&s->kobj);
> >  }
> > @@ -5770,7 +5756,6 @@ static int sysfs_slab_add(struct kmem_ca
> >  	}
> >  #endif
> > 
> > -	kobject_uevent(&s->kobj, KOBJ_ADD);
> >  	if (!unmergeable) {
> >  		/* Setup first alias */
> >  		sysfs_slab_alias(s, s->name);
> > @@ -5851,7 +5836,7 @@ static int __init slab_sysfs_init(void)
> > 
> >  	mutex_lock(&slab_mutex);
> > 
> > -	slab_kset = kset_create_and_add("slab", &slab_uevent_ops, kernel_kobj);
> > +	slab_kset = kset_create_and_add("slab", NULL, kernel_kobj);
> >  	if (!slab_kset) {
> >  		mutex_unlock(&slab_mutex);
> >  		pr_err("Cannot register slab subsystem.\n");
> 
> -- 
> Michal Hocko
> SUSE Labs

-- 
Michal Hocko
SUSE Labs