linux-kernel - Re: [PATCH v1] drivers/base/node.c: Simplify unregister_memory_block_under

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Date:   Fri, 19 Jul 2019 10:14:06 +0200
From:   David Hildenbrand <david@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     linux-mm@...ck.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Michal Hocko <mhocko@...e.com>,
        Oscar Salvador <osalvador@...e.de>
Subject: Re: [PATCH v1] drivers/base/node.c: Simplify
 unregister_memory_block_under_nodes()

On 18.07.19 16:22, David Hildenbrand wrote:
> We don't allow to offline memory block devices that belong to multiple
> numa nodes. Therefore, such devices can never get removed. It is
> sufficient to process a single node when removing the memory block.
> 
> Remember for each memory block if it belongs to no, a single, or mixed
> nodes, so we can use that information to skip unregistering or print a
> warning (essentially a safety net to catch BUGs).
> 
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: "Rafael J. Wysocki" <rafael@...nel.org>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: David Hildenbrand <david@...hat.com>
> Cc: Stephen Rothwell <sfr@...b.auug.org.au>
> Cc: Pavel Tatashin <pasha.tatashin@...een.com>
> Cc: Michal Hocko <mhocko@...e.com>
> Cc: Oscar Salvador <osalvador@...e.de>
> Signed-off-by: David Hildenbrand <david@...hat.com>
> ---
>  drivers/base/memory.c  |  1 +
>  drivers/base/node.c    | 40 ++++++++++++++++------------------------
>  include/linux/memory.h |  4 +++-
>  3 files changed, 20 insertions(+), 25 deletions(-)
> 
> diff --git a/drivers/base/memory.c b/drivers/base/memory.c
> index 20c39d1bcef8..154d5d4a0779 100644
> --- a/drivers/base/memory.c
> +++ b/drivers/base/memory.c
> @@ -674,6 +674,7 @@ static int init_memory_block(struct memory_block **memory,
>  	mem->state = state;
>  	start_pfn = section_nr_to_pfn(mem->start_section_nr);
>  	mem->phys_device = arch_get_memory_phys_device(start_pfn);
> +	mem->nid = NUMA_NO_NODE;
>  
>  	ret = register_memory(mem);
>  
> diff --git a/drivers/base/node.c b/drivers/base/node.c
> index 75b7e6f6535b..29d27b8d5fda 100644
> --- a/drivers/base/node.c
> +++ b/drivers/base/node.c
> @@ -759,8 +759,6 @@ static int register_mem_sect_under_node(struct memory_block *mem_blk,
>  	int ret, nid = *(int *)arg;
>  	unsigned long pfn, sect_start_pfn, sect_end_pfn;
>  
> -	mem_blk->nid = nid;
> -
>  	sect_start_pfn = section_nr_to_pfn(mem_blk->start_section_nr);
>  	sect_end_pfn = section_nr_to_pfn(mem_blk->end_section_nr);
>  	sect_end_pfn += PAGES_PER_SECTION - 1;
> @@ -789,6 +787,13 @@ static int register_mem_sect_under_node(struct memory_block *mem_blk,
>  			if (page_nid != nid)
>  				continue;
>  		}
> +
> +		/* this memory block spans this node */
> +		if (mem_blk->nid == NUMA_NO_NODE)
> +			mem_blk->nid = nid;
> +		else
> +			mem_blk->nid = NUMA_NO_NODE - 1;
> +

Although I am not sure if it can happen, I think it is better to have

if (mem_blk->nid == NUMA_NO_NODE)
	mem_blk->nid = nid;
else if (mem_blk->nid != nid)
	mem_blk->nid = NUMA_NO_NODE - 1;

-- 

Thanks,

David / dhildenb