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Subject: Re: [PATCH v3 0/8] Support DEVICE_GENERIC memory in migrate_vma_*
To:     Christoph Hellwig <hch@lst.de>
Cc:     Theodore Ts'o <tytso@mit.edu>, Alex Sierra <alex.sierra@amd.com>,
        akpm@linux-foundation.org, linux-mm@kvack.org,
        rcampbell@nvidia.com, linux-ext4@vger.kernel.org,
        linux-xfs@vger.kernel.org, amd-gfx@lists.freedesktop.org,
        dri-devel@lists.freedesktop.org, jgg@nvidia.com, jglisse@redhat.com
References: <20210617151705.15367-1-alex.sierra@amd.com>
 <YM9NXrGlhdp0qb7S@mit.edu> <905418d1-9099-0ea8-a6e6-84cc8ef3d0b0@amd.com>
 <20210624053048.GB25004@lst.de>
From:   Felix Kuehling <felix.kuehling@amd.com>
Message-ID: <3fd9dea5-6166-a92a-f9cb-e53f5590b2f8@amd.com>
Date:   Thu, 24 Jun 2021 11:08:30 -0400
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Am 2021-06-24 um 1:30 a.m. schrieb Christoph Hellwig:
> On Wed, Jun 23, 2021 at 05:49:55PM -0400, Felix Kuehling wrote:
>> For the reference counting changes we could use the dax driver with hmem 
>> and use efi_fake_mem on the kernel command line to create some 
>> DEVICE_GENERIC pages. I'm open to suggestions for good user mode tests to 
>> exercise dax functionality on this type of memory.
>>
>> For the migration helper changes we could modify or parametrize 
>> lib/hmm_test.c to create DEVICE_GENERIC pages instead of DEVICE_PRIVATE. 
>> Then run tools/testing/selftests/vm/hmm-tests.c.
> We'll also need a real in-tree user of the enhanced DEVICE_GENERIC memory.
> So while the refcounting cleanups early in the series are something I'd
> really like to see upstream as soon as everything is sorted out, the
> actual bits that can't only be used by your updated driver should wait
> for that.

The driver changes are pretty much ready to go.

But we have a bit of a chicken-egg problem because those changes likely
go through different trees. The GPU driver changes will go through
drm-next, but we can't merge them there until our dependencies have been
merged there from upstream. Unless we protect everything with some #ifdef.

Regards,
  Felix