RE: [PATCH v2 3/4] hv_balloon: update the NR_BALLOON_PAGES state

[Michael Kelley]

From: Nico Pache <npache@xxxxxxxxxx> Sent: Friday, March 14, 2025 2:38 PM
> 
> Update the NR_BALLOON_PAGES counter when pages are added to or
> removed from the Hyper-V balloon.
> 
> Signed-off-by: Nico Pache <npache@xxxxxxxxxx>
> ---
>  drivers/hv/hv_balloon.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c
> index fec2f18679e3..2b4080e51f97 100644
> --- a/drivers/hv/hv_balloon.c
> +++ b/drivers/hv/hv_balloon.c
> @@ -1192,6 +1192,7 @@ static void free_balloon_pages(struct hv_dynmem_device *dm,
>  		__ClearPageOffline(pg);
>  		__free_page(pg);
>  		dm->num_pages_ballooned--;
> +		mod_node_page_state(page_pgdat(pg), NR_BALLOON_PAGES, -1);
>  		adjust_managed_page_count(pg, 1);
>  	}
>  }
> @@ -1221,6 +1222,7 @@ static unsigned int alloc_balloon_pages(struct hv_dynmem_device *dm,
>  			return i * alloc_unit;
> 
>  		dm->num_pages_ballooned += alloc_unit;
> +		mod_node_page_state(page_pgdat(pg), NR_BALLOON_PAGES, alloc_unit);
> 
>  		/*
>  		 * If we allocatted 2M pages; split them so we
> --
> 2.48.1
> 

As is evident from the code, the hv_balloon driver already has accounting
for the number of pages that have been ballooned out of the VM. This
accounting and other details of the hv_balloon driver state is available in
/sys/kernel/debug/hv-balloon when CONFIG_DEBUGFS=y. But it seems OK
to also report the # of pages ballooned through /proc/meminfo, which
works even if CONFIG_DEBUGFS=n.

Reviewed-by: Michael Kelley <mhklinux@xxxxxxxxxxx>