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Date:   Fri, 30 Jul 2021 15:02:30 -0400
From:   Felix Kuehling <>
To:     "Sierra Guiza, Alejandro (Alex)" <>,
        "Theodore Y. Ts'o" <>
Subject: Re: [PATCH v3 0/8] Support DEVICE_GENERIC memory in migrate_vma_*

Am 2021-07-23 um 6:46 p.m. schrieb Sierra Guiza, Alejandro (Alex):
> On 7/17/2021 2:54 PM, Sierra Guiza, Alejandro (Alex) wrote:
>> On 7/16/2021 5:14 PM, Felix Kuehling wrote:
>>> Am 2021-07-16 um 11:07 a.m. schrieb Theodore Y. Ts'o:
>>>> On Wed, Jun 23, 2021 at 05:49:55PM -0400, Felix Kuehling wrote:
>>>>> I can think of two ways to test the changes for
>>>>> 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
>>>>> 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....
>>> No worries. Alejandro should have a new version of this series in a few
>>> days, with updates to hmm_test and some fixes.
>> V4 patch series have been sent for review.
>> Regards,
>> Alex Sierra
>>>> 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.
>>> That would be great!
>>> Regarding kernel config options, it should be the same as what you're
>>> using for DAX testing today. We're not changing or adding any Kconfig
>>> options. But let me take a stab:
>>> DEVICE_PRIVATE (maybe not needed for your test)
>>> FS_DAX
> Hi Theodore,
> I wonder if you had chance to set the kernel configs from Felix to
> enable DAX in xfstests.
> I've been trying to test FS DAX on my side using virtio-fs + QEMU.
> Unfortunately, Im having some problems setting up the environment with
> the guest kernel. Could you share your VM (QEMU or GCE) setup to run
> it with xfstests?
> Regards,
> Alex S.

Hi Theodore,

Sorry to keep bugging you. I'm wondering if you've had a chance to test
FS DAX with Alex's last patch series? ([PATCH v4 00/13] Support
DEVICE_GENERIC memory in migrate_vma_*) I think other than minor
cosmetic fixes, this should be ready to merge, if it passes your tests.


>>> I'm not sure what you're looking for in terms of kernel command line,
>>> other than the memmap options you already found. There are some more
>>> options to run hmm_test with fake SPM (DEVICE_GENERIC) memory, but
>>> we're
>>> already running that ourselves. That will also be in the next revision
>>> of this patch series.
>> In order to run hmm test with generic device type enabled, set the
>> following:
>> kernel config:
>> Kernel parameters to fake SP memory. The addresses set here are based
>> on my system's usable memory enumerated by BIOS-e820 at boot. The
>> test requires two SP devices of at least 256MB.
>> efi_fake_mem=1G@...00000000:0x40000,1G@...40000000:0x40000
>> To run the hmm_test in generic device type pass the SP addresses to
>> the sh script.
>> sudo ./ smoke 0x100000000 0x140000000
>>> If you can run your xfstests with DAX on top of this patch series, that
>>> would be very helpful. That's to make sure the ZONE_DEVICE page
>>> refcount
>>> changes don't break DAX.
>>> Regards,
>>>    Felix
>>>> Cheers,
>>>>                         - Ted

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