RE: [PATCH v2 3/4] hv_balloon: update the NR_BALLOON_PAGES state
From: Michael Kelley
Date: Sat Mar 15 2025 - 00:09:42 EST
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>