linux-kernel - Re: [PATCH v8 2/3] mm/mempolicy: Prepare weighted interleave sysfs for memory hotplug

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Message-ID: <20250417015600.661-1-rakie.kim@sk.com>
Date: Thu, 17 Apr 2025 10:55:52 +0900
From: Rakie Kim <rakie.kim@...com>
To: Dan Williams <dan.j.williams@...el.com>
Cc: gourry@...rry.net,
	linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	linux-cxl@...r.kernel.org,
	joshua.hahnjy@...il.com,
	ying.huang@...ux.alibaba.com,
	david@...hat.com,
	Jonathan.Cameron@...wei.com,
	osalvador@...e.de,
	kernel_team@...ynix.com,
	honggyu.kim@...com,
	yunjeong.mun@...com,
	rakie.kim@...com,
	akpm@...ux-foundation.org
Subject: Re: [PATCH v8 2/3] mm/mempolicy: Prepare weighted interleave sysfs for memory hotplug

On Wed, 16 Apr 2025 16:07:18 -0700 Dan Williams <dan.j.williams@...el.com> wrote:
> Rakie Kim wrote:
> > Previously, the weighted interleave sysfs structure was statically
> > managed during initialization. This prevented new nodes from being
> > recognized when memory hotplug events occurred, limiting the ability
> > to update or extend sysfs entries dynamically at runtime.
> > 
> > To address this, this patch refactors the sysfs infrastructure and
> > encapsulates it within a new structure, `sysfs_wi_group`, which holds
> > both the kobject and an array of node attribute pointers.
> > 
> > By allocating this group structure globally, the per-node sysfs
> > attributes can be managed beyond initialization time, enabling
> > external modules to insert or remove node entries in response to
> > events such as memory hotplug or node online/offline transitions.
> > 
> > Instead of allocating all per-node sysfs attributes at once, the
> > initialization path now uses the existing sysfs_wi_node_add() and
> > sysfs_wi_node_delete() helpers. This refactoring makes it possible
> > to modularly manage per-node sysfs entries and ensures the
> > infrastructure is ready for runtime extension.
> > 
> > Signed-off-by: Rakie Kim <rakie.kim@...com>
> > Reviewed-by: Gregory Price <gourry@...rry.net>
> > Reviewed-by: Joshua Hahn <joshua.hahnjy@...il.com>
> > ---
> >  mm/mempolicy.c | 60 ++++++++++++++++++++++++--------------------------
> >  1 file changed, 29 insertions(+), 31 deletions(-)
> > 
> > diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> > index dcf03c389b51..998635127e9d 100644
> > --- a/mm/mempolicy.c
> > +++ b/mm/mempolicy.c
> > @@ -3419,6 +3419,13 @@ struct iw_node_attr {
> >  	int nid;
> >  };
> >  
> > +struct sysfs_wi_group {
> > +	struct kobject wi_kobj;
> > +	struct iw_node_attr *nattrs[];
> > +};
> > +
> > +static struct sysfs_wi_group *wi_group;
> > +
> >  static ssize_t node_show(struct kobject *kobj, struct kobj_attribute *attr,
> >  			 char *buf)
> >  {
> > @@ -3461,24 +3468,23 @@ static ssize_t node_store(struct kobject *kobj, struct kobj_attribute *attr,
> >  	return count;
> >  }
> >  
> > -static struct iw_node_attr **node_attrs;
> > -
> > -static void sysfs_wi_node_delete(struct iw_node_attr *node_attr,
> > -				 struct kobject *parent)
> > +static void sysfs_wi_node_delete(int nid)
> >  {
> > -	if (!node_attr)
> > +	if (!wi_group->nattrs[nid])
> >  		return;
> > -	sysfs_remove_file(parent, &node_attr->kobj_attr.attr);
> > -	kfree(node_attr->kobj_attr.attr.name);
> > -	kfree(node_attr);
> > +
> > +	sysfs_remove_file(&wi_group->wi_kobj,
> > +			  &wi_group->nattrs[nid]->kobj_attr.attr);
> > +	kfree(wi_group->nattrs[nid]->kobj_attr.attr.name);
> > +	kfree(wi_group->nattrs[nid]);
> >  }
> >  
> > -static void sysfs_wi_node_delete_all(struct kobject *wi_kobj)
> > +static void sysfs_wi_node_delete_all(void)
> >  {
> >  	int nid;
> >  
> >  	for (nid = 0; nid < nr_node_ids; nid++)
> > -		sysfs_wi_node_delete(node_attrs[nid], wi_kobj);
> > +		sysfs_wi_node_delete(nid);
> >  }
> >  
> >  static void iw_table_free(void)
> > @@ -3501,8 +3507,7 @@ static void iw_table_free(void)
> >  static void wi_kobj_release(struct kobject *wi_kobj)
> >  {
> >  	iw_table_free();
> > -	kfree(node_attrs);
> > -	kfree(wi_kobj);
> > +	kfree(wi_group);
> 
> Ah, look just one more iw_table_free() deletion to be able to switch to
> kobject_create_and_add() flow.
> 
> For what this patch is though you can add:
> 
> Reviewed-by: Dan Williams <dan.j.williams@...el.com>

Thank you for the suggestion.
I have already removed the iw_table_free() and kfree(node_attrs) from
the release path in Patch1 as part of wi_cleanup().

Rakie