Re: [Xen-devel] [PATCH v1 09/10] mm/memory_hotplug: Don't mark pages PG_reserved when initializing the memmap

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 10/24/19 8:09 AM, David Hildenbrand wrote:
> diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
> index 4f2e78a5e4db..af69f057913a 100644
> --- a/drivers/xen/balloon.c
> +++ b/drivers/xen/balloon.c
> @@ -374,6 +374,13 @@ static void xen_online_page(struct page *page, unsigned 
> int order)
>       mutex_lock(&balloon_mutex);
>       for (i = 0; i < size; i++) {
>               p = pfn_to_page(start_pfn + i);
> +             /*
> +              * TODO: The core used to mark the pages reserved. Most probably
> +              * we can stop doing that now. However, especially
> +              * alloc_xenballooned_pages() left PG_reserved set
> +              * on pages that can get mapped to user space.
> +              */
> +             __SetPageReserved(p);

I suspect this is not needed. Pages can get into balloon either from
here or from non-hotplug path (e.g. decrease_reservation()) and so when
we get a page from the balloon we would get a random page that may or
may not have Reserved bit set.

-boris


>               balloon_append(p);
>       }
>       mutex_unlock(&balloon_mutex);
>


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