Re: [PATCH RESEND 0/9] selftests/mm: improve mremap_test

[Kalesh Singh]

On Mon, Sep 28, 2026 at 10:54 PM Sarthak Sharma <sarthak.sharma@xxxxxxx> wrote:
>
>
>
> On 9/24/26 10:30 AM, Sarthak Sharma wrote:
> > This series fixes several correctness issues in mremap_test and
> > simplifies and strengthens its data validation.
> >
> > Patch 1 converts the mremap_test to use kselftest helpers, removes
> > manual tracking of failed tests and corrects some spelling errors.
> >
> > Patches 2 to 5 fix userfaultfd skipping, unexpected mremap success
> > handling, multi-VMA data validation and failure reporting when data
> > corruption is detected.
> >
> > Patch 6 removes the randomization and uses a simple pattern based approach.
> >
> > Patch 7 removes perf tests and timing infrastructure.
> >
> > Patch 8 removes validation threshold and always validates complete mappings.
> >
> > Patch 9 strengthens the multi VMA validation by also checking the
> > mapping state of holes after remapping.
>
> Hello everyone! Just wanted to check if someone has had a chance to look
> at the series.
>
> Also, Sashiko has a concern [1], and I had the same while posting the
> series. I hope I can get some opinion from the community.
>
> Currently, for PUD remap tests, we allocate a source mapping of 2GB. We
> only fault in the first threshold_mb amount of memory, remap the whole
> region, and validate the already faulted threshold_mb amount of memory,
> which is, by default, equal to 4MB and can be changed by the user by
> supplying a command line option.
>
> Since we plan to remove all command line options from teh selftests, I
> removed threshold_mb altogether, following some discussion on the list
> [2]. This would now cause a 2GB source mapping, and its contents copied
> from another 2GB buffer. This causes the process to have a 4GB RSS.
> Sashiko says that this can cause OOM killing in small CI machines.
>
> Would it be okay to keep a 4GB RSS in this case, or should we find some
> other way of validating a part of the whole range instead?

Hi Sarthak,

IIRC when I initially introduced the test, John was concerned that
validating the whole range would significantly increase the duration
of the mm selftests; this is why the threshold was introduced. Please
check how much it increases if we validate the full range (with
David's suggestions) and if it's no longer a concern from other folks.
I am fine with removing the threshold.

Thanks,
Kalesh

>
> [1]
> https://sashiko.dev/#/patchset/20260924050009.19974-1-sarthak.sharma%40arm.com
>
> [2]
> https://lore.kernel.org/all/2e34b619-085f-4a9c-bb41-bc024fd40dd7@xxxxxxxxxx/