Re: [PATCH v2 2/2] mm: migrate: Allocate the node_demotion structure dynamically

[Huang, Ying]

Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx> writes:

> For the worst case (MAX_NUMNODES=1024), the node_demotion structure can
> consume 32k bytes, which appears too large, so we can change to allocate
> node_demotion dynamically at initialization time. Meanwhile allocating
> the target demotion nodes array dynamically to select a suitable size
> according to the MAX_NUMNODES.
>
> Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
> ---
>  mm/migrate.c | 38 +++++++++++++++++++++++++++++---------
>  1 file changed, 29 insertions(+), 9 deletions(-)
>
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 126e9e6..0145b38 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -1152,10 +1152,11 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
>  #define DEFAULT_DEMOTION_TARGET_NODES 15
>  struct demotion_nodes {
>  	unsigned short nr;
> -	short nodes[DEFAULT_DEMOTION_TARGET_NODES];
> +	short nodes[];
>  };
>  
> -static struct demotion_nodes node_demotion[MAX_NUMNODES] __read_mostly;
> +static struct demotion_nodes *node_demotion[MAX_NUMNODES] __read_mostly;
> +static unsigned short target_nodes_max;

I think we can use something as below,

  #if MAX_NUMNODES < DEFAULT_DEMOTION_TARGET_NODES
  #define DEMOTION_TARGET_NODES   (MAX_NUMNODES - 1)
  #else
  #define DEMOTION_TARGET_NODES   DEFAULT_DEMOTION_TARGET_NODES
  #endif

  static struct demotion_nodes *node_demotion;

Then we can allocate nr_node_ids * sizeof(struct demotion_nodes) for node_demotion.

Best Regards,
Huang, Ying

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