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Date:   Sat, 9 May 2020 17:16:12 -0700
From:   Andrew Morton <akpm@linux-foundation.org>
To:     Jason Gunthorpe <jgg@ziepe.ca>
Cc:     linux-mm@kvack.org, Ralph Campbell <rcampbell@nvidia.com>,
        Alex Deucher <alexander.deucher@amd.com>,
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        Niranjana Vishwanathapura <niranjana.vishwanathapura@intel.com>,
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Subject: Re: [PATCH hmm v2 1/5] mm/hmm: make CONFIG_DEVICE_PRIVATE into a
 select
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On Fri,  1 May 2020 15:20:44 -0300 Jason Gunthorpe <jgg@ziepe.ca> wrote:

> From: Jason Gunthorpe <jgg@mellanox.com>
> 
> There is no reason for a user to select this or not directly - it should
> be selected by drivers that are going to use the feature, similar to how
> CONFIG_HMM_MIRROR works.
> 
> Currently all drivers provide a feature kconfig that will disable use of
> DEVICE_PRIVATE in that driver, allowing users to avoid enabling this if
> they don't want the overhead.
> 

I'm not too sure what's going on here, but i386 allmodconfig broke.

kernel/resource.c: In function '__request_free_mem_region':
kernel/resource.c:1653:28: error: 'PA_SECTION_SHIFT' undeclared (first use in this function); did you mean 'SECTIONS_PGSHIFT'?
  size = ALIGN(size, 1UL << PA_SECTION_SHIFT);

because in current mainline, allmodconfig produces
CONFIG_DEVICE_PRIVATE=n but in current linux-next, allmodconfig
produces CONFIG_DEVICE_PRIVATE=y.  But CONFIG_SPARSEMEM=n so the build
breaks.

Bisection fingers this commit, but reverting it doesn't seem to fix
things.  Could you take a look please?

I'm seeing this from menuconfig:

WARNING: unmet direct dependencies detected for DEVICE_PRIVATE
  Depends on [n]: ZONE_DEVICE [=n]
  Selected by [m]:
  - DRM_NOUVEAU_SVM [=y] && HAS_IOMEM [=y] && DRM_NOUVEAU [=m] && MMU [=y] && STAGING [=y]
  - TEST_HMM [=m] && RUNTIME_TESTING_MENU [=y] && TRANSPARENT_HUGEPAGE [=y]

`select' rather sucks this way - easy to break dependencies.  Quite a
number of years ago the Kconfig gurus were saying "avoid", but I don't
recall the details.