linux-kernel - Re: [PATCH v2 1/1] mm/vmscan.c: Prevent allocating shrinker

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Date:   Tue, 7 Dec 2021 23:34:00 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Nico Pache <npache@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        akpm@...ux-foundation.org, shakeelb@...gle.com,
        ktkhai@...tuozzo.com, shy828301@...il.com, guro@...com,
        vbabka@...e.cz, vdavydov.dev@...il.com, raquini@...hat.com,
        mhocko@...e.com, david@...hat.com
Subject: Re: [PATCH v2 1/1] mm/vmscan.c: Prevent allocating shrinker_info on
 offlined nodes

On Tue, Dec 07, 2021 at 05:40:13PM -0500, Nico Pache wrote:
> +++ b/mm/vmscan.c
> @@ -222,13 +222,16 @@ static int expand_one_shrinker_info(struct mem_cgroup *memcg,
>  	int size = map_size + defer_size;
>  
>  	for_each_node(nid) {
> +		int tmp = nid;
>  		pn = memcg->nodeinfo[nid];
>  		old = shrinker_info_protected(memcg, nid);
>  		/* Not yet online memcg */
>  		if (!old)
>  			return 0;
>  
> -		new = kvmalloc_node(sizeof(*new) + size, GFP_KERNEL, nid);
> +		if(!node_online(nid))
> +			tmp = numa_mem_id();
> +		new = kvmalloc_node(sizeof(*new) + size, GFP_KERNEL, tmp);
>  		if (!new)

Why should this be fixed here and not in, say, kvmalloc_node()?