Message-ID: <a1c3e952-866d-e3b4-1479-8f04e963bf11@redhat.com>
Date:   Tue, 7 Dec 2021 19:25:25 -0500
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Subject: Re: [PATCH v2 1/1] mm/vmscan.c: Prevent allocating shrinker_info on
 offlined nodes
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To:     Matthew Wilcox <willy@infradead.org>, mhocko@suse.com
Cc:     linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        akpm@linux-foundation.org, shakeelb@google.com,
        ktkhai@virtuozzo.com, shy828301@gmail.com, guro@fb.com,
        vbabka@suse.cz, vdavydov.dev@gmail.com, raquini@redhat.com,
        david@redhat.com
References: <20211207224013.880775-1-npache@redhat.com>
 <20211207224013.880775-2-npache@redhat.com>
 <Ya/vaGdKHm6Zy3ML@casper.infradead.org>
From:   Nico Pache <npache@redhat.com>
In-Reply-To: <Ya/vaGdKHm6Zy3ML@casper.infradead.org>
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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.
>