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Date:   Fri, 16 Jul 2021 11:07:40 -0400
From:   "Theodore Y. Ts'o" <tytso@mit.edu>
To:     Felix Kuehling <felix.kuehling@amd.com>
Cc:     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,
        hch@lst.de, jgg@nvidia.com, jglisse@redhat.com
Subject: Re: [PATCH v3 0/8] Support DEVICE_GENERIC memory in migrate_vma_*
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On Wed, Jun 23, 2021 at 05:49:55PM -0400, Felix Kuehling wrote:
> 
> I can think of two ways to test the changes for MEMORY_DEVICE_GENERIC in
> this patch series in a way that is reproducible without special hardware and
> firmware:
> 
> 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.

Sorry for the thread necromancy, but now that the merge window is
past....

Today I test ext4's dax support, without having any $$$ DAX hardware,
by using the kernel command line "memmap=4G!9G:memmap=9G!14G" which
reserves memory so that creates two pmem device and then I run
xfstests with DAX enabled using qemu or using a Google Compute Engine
VM, using TEST_DEV=/dev/pmem0 and SCRATCH_DEV=/dev/pmem1.

If you can give me a recipe for what kernel configs I should enable,
and what magic kernel command line arguments to use, then I'd be able
to test your patch set with ext4.

Cheers,

						- Ted