Re: [PATCH] mm: add comments on pglist_data zones

[Matthew Wilcox <willy@infradead.org>]

On Wed, May 20, 2020 at 01:54:43PM -0700, Ben Widawsky wrote:
> While making other modifications it was easy to confuse the two struct
> members node_zones and node_zonelists. For those already familiar with
> the code, this might seem to be a silly patch, but it's quite helpful to
> disambiguate the similar-sounding fields
> 
> While here, add a small comment on why nr_zones isn't simply MAX_NR_ZONES

It seems like a real shame to write all this excellent documentation
and not format it as kernel-doc.

> Signed-off-by: Ben Widawsky <ben.widawsky@intel.com>
> ---
>  include/linux/mmzone.h | 14 +++++++++++++-
>  1 file changed, 13 insertions(+), 1 deletion(-)
> 
> diff --git include/linux/mmzone.h include/linux/mmzone.h
> index 1b9de7d220fb..4f7c95e9bad8 100644
> --- include/linux/mmzone.h
> +++ include/linux/mmzone.h
> @@ -665,9 +665,21 @@ struct deferred_split {
>   * per-zone basis.
>   */
>  typedef struct pglist_data {
> +	/*
> +	 * node_zones contains just the zones for THIS node. Not all of the
> +	 * zones may be populated, but it is the full list. It is referenced by
> +	 * this node's node_zonelists as well as other node's node_zonelists.
> +	 */
>  	struct zone node_zones[MAX_NR_ZONES];
> +
> +	/*
> +	 * node_zonelists contains references to all zones in all nodes.
> +	 * Generally the first zones will be references to this node's
> +	 * node_zones.
> +	 */
>  	struct zonelist node_zonelists[MAX_ZONELISTS];
> -	int nr_zones;
> +
> +	int nr_zones; /* number of populated zones in this node */
>  #ifdef CONFIG_FLAT_NODE_MEM_MAP	/* means !SPARSEMEM */
>  	struct page *node_mem_map;
>  #ifdef CONFIG_PAGE_EXTENSION
> -- 
> 2.26.2
> 
>