linux-kernel - Re: [Nouveau] [PATCH 22/22] mm: don't select MIGRATE_VMA_HELPER from HMM

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Date:   Thu, 13 Jun 2019 18:53:15 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     Christoph Hellwig <hch@....de>,
        Dan Williams <dan.j.williams@...el.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        Jason Gunthorpe <jgg@...lanox.com>,
        Ben Skeggs <bskeggs@...hat.com>
CC:     <linux-nvdimm@...ts.01.org>, <linux-pci@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>,
        <linux-mm@...ck.org>, <nouveau@...ts.freedesktop.org>
Subject: Re: [Nouveau] [PATCH 22/22] mm: don't select MIGRATE_VMA_HELPER from
 HMM_MIRROR

On 6/13/19 2:43 AM, Christoph Hellwig wrote:
> The migrate_vma helper is only used by noveau to migrate device private
> pages around.  Other HMM_MIRROR users like amdgpu or infiniband don't
> need it.
> 
> Signed-off-by: Christoph Hellwig <hch@....de>
> ---
>  drivers/gpu/drm/nouveau/Kconfig | 1 +
>  mm/Kconfig                      | 1 -
>  2 files changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/nouveau/Kconfig b/drivers/gpu/drm/nouveau/Kconfig
> index 66c839d8e9d1..96b9814e6d06 100644
> --- a/drivers/gpu/drm/nouveau/Kconfig
> +++ b/drivers/gpu/drm/nouveau/Kconfig
> @@ -88,6 +88,7 @@ config DRM_NOUVEAU_SVM
>  	depends on DRM_NOUVEAU
>  	depends on HMM_MIRROR
>  	depends on STAGING
> +	select MIGRATE_VMA_HELPER
>  	default n
>  	help
>  	  Say Y here if you want to enable experimental support for
> diff --git a/mm/Kconfig b/mm/Kconfig
> index 73676cb4693f..eca88679b624 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -679,7 +679,6 @@ config HMM_MIRROR
>  	bool "HMM mirror CPU page table into a device page table"
>  	depends on MMU
>  	select MMU_NOTIFIER
> -	select MIGRATE_VMA_HELPER
>  	help
>  	  Select HMM_MIRROR if you want to mirror range of the CPU page table of a
>  	  process into a device page table. Here, mirror means "keep synchronized".
> 

For those who have out of tree drivers that need migrate_vma(), but are not
Nouveau, could we pretty please allow a way to select that independently?

It's not a big deal, as I expect the Nouveau option will normally be selected, 
but it would be nice. Because there is a valid configuration that involves 
Nouveau not being selected, but our driver still wanting to run.

Maybe we can add something like this on top of what you have?

diff --git a/mm/Kconfig b/mm/Kconfig
index eca88679b624..330996632513 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -670,7 +670,10 @@ config ZONE_DEVICE
          If FS_DAX is enabled, then say Y.
 
 config MIGRATE_VMA_HELPER
-       bool
+       bool "migrate_vma() helper routine"
+       help
+         Provides a migrate_vma() routine that GPUs and other
+         device drivers may need.
 
 config DEV_PAGEMAP_OPS
        bool



thanks,
-- 
John Hubbard
NVIDIA