linux-kernel - Re: [PATCH v1 2/2] drivers/base/memory: determine and store zone for single-zone memory blocks

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Message-ID: <10293d6c-c2d6-2277-0634-bdd237fc23de@redhat.com>
Date:   Mon, 31 Jan 2022 12:42:49 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Oscar Salvador <osalvador@...e.de>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Michal Hocko <mhocko@...e.com>,
        Rafael Parra <rparrazo@...hat.com>
Subject: Re: [PATCH v1 2/2] drivers/base/memory: determine and store zone for
 single-zone memory blocks

[...] having accidentally skipped two comments.


> 
>> There are three scenarios to handle:
> ...
> ...
> 
>> @@ -225,6 +226,9 @@ static int memory_block_offline(struct memory_block *mem)
>>  	unsigned long nr_vmemmap_pages = mem->nr_vmemmap_pages;
>>  	int ret;
>>  
>> +	if (!mem->zone)
>> +		return -EBUSY;
> 
> Should not we return -EINVAL? I mean, -EBUSY reads like this might be a
> temporary error which might get fixed later on, but that isn't the case.

We should, and I could have sworn I fixed that up last-minute.

>> +static struct zone *early_node_zone_for_memory_block(struct memory_block *mem,
>> +						     int nid)
>> +{
>> +	const unsigned long start_pfn = section_nr_to_pfn(mem->start_section_nr);
>> +	const unsigned long nr_pages = PAGES_PER_SECTION * sections_per_block;
>> +	struct zone *zone, *matching_zone = NULL;
>> +	pg_data_t *pgdat = NODE_DATA(nid);
> 
> I was about to complain because in init_memory_block() you call
> early_node_zone_for_memory_block() with nid == NUMA_NODE_NODE, but then
> I saw that NODE_DATA on !CONFIG_NUMA falls to contig_page_data.
> So, I guess we cannot really reach this on CONFIG_NUMA machines with nid
> being NUMA_NO_NODE, right? (do we want to add a check just in case?)
> 
>> +#ifdef CONFIG_NUMA
>> +void memory_block_set_nid(struct memory_block *mem, int nid,
>> +			  enum meminit_context context)
> 
> But we also set the zone? (Only for boot memory)

Yes, it's derived from the node internally, though, and not supplied
explicitly. Renaming it could be misleading IMHO.

-- 
Thanks,

David / dhildenb