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Subject: Re: [PATCH 2/2] xen: enable BALLOON_MEMORY_HOTPLUG by default
To:     Roger Pau Monne <roger.pau@citrix.com>,
        linux-kernel@vger.kernel.org
Cc:     Ian Jackson <ian.jackson@eu.citrix.com>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Stefano Stabellini <sstabellini@kernel.org>,
        xen-devel@lists.xenproject.org
References: <20200324150015.50496-1-roger.pau@citrix.com>
 <20200324150015.50496-2-roger.pau@citrix.com>
From:   =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= <jgross@suse.com>
Message-ID: <f4ce1d95-c80a-8727-7ddc-9199bb2036c4@suse.com>
Date:   Tue, 24 Mar 2020 16:09:35 +0100
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On 24.03.20 16:00, Roger Pau Monne wrote:
> Without it a PVH dom0 is mostly useless, as it would balloon down huge
> amounts of RAM in order get physical address space to map foreign
> memory and grants, ultimately leading to an out of memory situation.
> 
> Such option is also needed for HVM or PVH driver domains, since they
> also require mapping grants into physical memory regions.
> 
> Suggested-by: Ian Jackson <ian.jackson@eu.citrix.com>
> Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
> ---
> Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
> Cc: Juergen Gross <jgross@suse.com>
> Cc: Stefano Stabellini <sstabellini@kernel.org>
> Cc: xen-devel@lists.xenproject.org
> ---
>   drivers/xen/Kconfig | 1 +
>   1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/xen/Kconfig b/drivers/xen/Kconfig
> index 57ddd6f4b729..c344bcffd89d 100644
> --- a/drivers/xen/Kconfig
> +++ b/drivers/xen/Kconfig
> @@ -13,6 +13,7 @@ config XEN_BALLOON
>   config XEN_BALLOON_MEMORY_HOTPLUG
>   	bool "Memory hotplug support for Xen balloon driver"
>   	depends on XEN_BALLOON && MEMORY_HOTPLUG
> +	default y
>   	help
>   	  Memory hotplug support for Xen balloon driver allows expanding memory
>   	  available for the system above limit declared at system startup.
> 

Another variant would be to set: default XEN_BACKEND

This would match the reasoning for switching it on.

Either way would be fine with me, so you can add

Reviewed-by: Juergen Gross <jgross@suse.com>


Juergen