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

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Date:   Tue, 7 Dec 2021 19:25:25 -0500
From:   Nico Pache <npache@...hat.com>
To:     Matthew Wilcox <willy@...radead.org>, mhocko@...e.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,
        david@...hat.com
Subject: Re: [PATCH v2 1/1] mm/vmscan.c: Prevent allocating shrinker_info on
 offlined nodes



On 12/7/21 18:34, Matthew Wilcox wrote:
> 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()?

according to Michal, the caller should be responsible for making sure it is
allocating on a correct node. This avoids adding branches to hot-paths and
wasting cycles. Im not opposed to moving it to kvmalloc_node, but it may result
in masking other issues from other callers.
>