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Date:   Fri, 16 Jul 2021 18:14:05 -0400
From:   Felix Kuehling <>
To:     "Theodore Y. Ts'o" <>
Cc:     Alex Sierra <>,,,,,,,,,,
Subject: Re: [PATCH v3 0/8] Support DEVICE_GENERIC memory in migrate_vma_*

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 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....

No worries. Alejandro should have a new version of this series in a few
days, with updates to hmm_test and some fixes.

> 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)

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.

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.


> Cheers,
> 						- Ted

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