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From: "Jürgen Groß" <jgross@suse.com>
To: "Roger Pau Monné" <roger.pau@citrix.com>,
	"Christoph Hellwig" <hch@infradead.org>
Cc: linux-kernel@vger.kernel.org,
	Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>,
	David Airlie <airlied@linux.ie>, Daniel Vetter <daniel@ffwll.ch>,
	Boris Ostrovsky <boris.ostrovsky@oracle.com>,
	Stefano Stabellini <sstabellini@kernel.org>,
	Dan Carpenter <dan.carpenter@oracle.com>, Wei Liu <wl@xen.org>,
	Yan Yankovskyi <yyankovskyi@gmail.com>,
	dri-devel@lists.freedesktop.org, xen-devel@lists.xenproject.org,
	linux-mm@kvack.org, David Hildenbrand <david@redhat.com>,
	Michal Hocko <mhocko@kernel.org>,
	Dan Williams <dan.j.williams@intel.com>
Subject: Re: [PATCH v4 2/2] xen: add helpers to allocate unpopulated memory
Date: Fri, 14 Aug 2020 12:27:32 +0200	[thread overview]
Message-ID: <a907ff4a-c887-7d02-1d45-140d7749afa4@suse.com> (raw)
In-Reply-To: <20200814095629.GJ975@Air-de-Roger>

On 14.08.20 11:56, Roger Pau Monné wrote:
> On Fri, Aug 14, 2020 at 08:29:20AM +0100, Christoph Hellwig wrote:
>> On Thu, Aug 13, 2020 at 09:54:20AM +0200, Roger Pau Monn?? wrote:
>>> On Thu, Aug 13, 2020 at 08:33:37AM +0100, Christoph Hellwig wrote:
>>>> On Tue, Aug 11, 2020 at 11:44:47AM +0200, Roger Pau Monne wrote:
>>>>> If enabled (because ZONE_DEVICE is supported) the usage of the new
>>>>> functionality untangles Xen balloon and RAM hotplug from the usage of
>>>>> unpopulated physical memory ranges to map foreign pages, which is the
>>>>> correct thing to do in order to avoid mappings of foreign pages depend
>>>>> on memory hotplug.
>>>>
>>>> So please just select ZONE_DEVICE if this is so much better rather
>>>> than maintaining two variants.
>>>
>>> We still need to other variant for Arm at least, so both need to be
>>> maintained anyway, even if we force ZONE_DEVICE on x86.
>>
>> Well, it still really helps reproducability if you stick to one
>> implementation of x86.
>>
>> The alternative would be an explicit config option to opt into it,
>> but just getting a different implementation based on a random
>> kernel option is strange.
> 
> Would adding something like the chunk below to the patch be OK?
> 
> ---8<---
> diff --git a/drivers/xen/Kconfig b/drivers/xen/Kconfig
> index 018020b91baa..5f321a1319e6 100644
> --- a/drivers/xen/Kconfig
> +++ b/drivers/xen/Kconfig
> @@ -328,7 +328,14 @@ config XEN_FRONT_PGDIR_SHBUF
>   	tristate
>   
>   config XEN_UNPOPULATED_ALLOC
> -	bool
> -	default y if ZONE_DEVICE && !ARM && !ARM64
> +	bool "Use unpopulated memory ranges for guest mappings"
> +	depends on X86
> +	select ZONE_DEVICE
> +	default y

I'd rather use "default XEN_BACKEND" here, as mappings of other guest's
memory is rarely used for non-backend guests.


Juergen



  reply	other threads:[~2020-08-14 10:28 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-11  9:44 [PATCH v4 0/2] xen/balloon: fixes for memory hotplug Roger Pau Monne
2020-08-11  9:44 ` [PATCH v4 1/2] memremap: rename MEMORY_DEVICE_DEVDAX to MEMORY_DEVICE_GENERIC Roger Pau Monne
2020-08-11 21:07   ` David Hildenbrand
2020-08-20 11:37     ` Roger Pau Monné
2020-08-31 10:19       ` Roger Pau Monné
2020-08-31 20:56         ` Ira Weiny
2020-08-31 19:20   ` Andrew Morton
2020-08-11  9:44 ` [PATCH v4 2/2] xen: add helpers to allocate unpopulated memory Roger Pau Monne
2020-08-12  7:28   ` Jürgen Groß
2020-08-12  7:38     ` Roger Pau Monné
2020-08-13  7:33   ` Christoph Hellwig
2020-08-13  7:54     ` Roger Pau Monné
2020-08-13  9:49       ` Daniel Vetter
2020-08-13 10:02         ` Roger Pau Monné
2020-08-14  7:29       ` Christoph Hellwig
2020-08-14  9:56         ` Roger Pau Monné
2020-08-14 10:27           ` Jürgen Groß [this message]
2020-08-14 12:47             ` Roger Pau Monné
2020-08-14 12:54               ` Jürgen Groß
2020-08-14 13:35                 ` Roger Pau Monné
2020-08-14 13:52                   ` Jürgen Groß

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