linux-kernel - Re: [RFC PATCH 10/15] virtio: virtio_balloon: use PAGES_PER_SECTION instead of MAX_ORDER_NR

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Date:   Mon, 9 Aug 2021 09:42:26 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Zi Yan <ziy@...dia.com>, linux-mm@...ck.org
Cc:     Matthew Wilcox <willy@...radead.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Michal Hocko <mhocko@...nel.org>,
        John Hubbard <jhubbard@...dia.com>,
        linux-kernel@...r.kernel.org,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        virtualization@...ts.linux-foundation.org
Subject: Re: [RFC PATCH 10/15] virtio: virtio_balloon: use PAGES_PER_SECTION
 instead of MAX_ORDER_NR_PAGES.

On 05.08.21 21:02, Zi Yan wrote:
> From: Zi Yan <ziy@...dia.com>
> 
> It keeps the existing behavior when MAX_ORDER grows beyond a section.
> 

... but it breaks/changes existing behavior if MAX_ORDER is smaller than 
a section?

> Signed-off-by: Zi Yan <ziy@...dia.com>
> Cc: "Michael S. Tsirkin" <mst@...hat.com>
> Cc: David Hildenbrand <david@...hat.com>
> Cc: Jason Wang <jasowang@...hat.com>
> Cc: virtualization@...ts.linux-foundation.org
> Cc: linux-mm@...ck.org
> Cc: linux-kernel@...r.kernel.org
> ---
>   drivers/virtio/virtio_balloon.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index 47dce91f788c..de8d0355d827 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -36,7 +36,7 @@
>   #define VIRTIO_BALLOON_FREE_PAGE_ALLOC_FLAG (__GFP_NORETRY | __GFP_NOWARN | \
>   					     __GFP_NOMEMALLOC)
>   /* The order of free page blocks to report to host */
> -#define VIRTIO_BALLOON_HINT_BLOCK_ORDER (MAX_ORDER - 1)
> +#define VIRTIO_BALLOON_HINT_BLOCK_ORDER (PFN_SECTION_SHIFT - 1)
>   /* The size of a free page block in bytes */
>   #define VIRTIO_BALLOON_HINT_BLOCK_BYTES \
>   	(1 << (VIRTIO_BALLOON_HINT_BLOCK_ORDER + PAGE_SHIFT))
> 


-- 
Thanks,

David / dhildenb