could not turn DAMON with damo schemes

[honggyukim]

I have updated my damo repo based on the current next branch, but I see an error when running damo schemes as follows.

$ cat pageout.json
[
    {
        "action": "pageout",
        "access_pattern": {
            "sz_bytes": {"min": "4.000 KiB", "max": "max"},
            "nr_accesses": {"min": "0 %", "max": "0 %"},
            "age": {"min": "1 s", "max": "max"}
        }
    }
]

$ ./damo schemes -c pageout.json
could not turn DAMON on (cannot apply kdamonds from args (filepath (/sys/kernel/mm/damon/admin/kdamonds/0/contexts/0/schemes/0/apply_interval_us) is neither dir nor file))

It works fine on the previous version at 0c48a1f.

My kernel version is based on v6.4.

[honggyukim]

damo start and damo stop works fine, but only damo schemes doesn't work in this case.

[honggyukim]

git bisect shows the following 07c8a6a is the bad commit.

07c8a6a5847895b9a357563b6a50a25618d4273c is the first bad commit
commit 07c8a6a5847895b9a357563b6a50a25618d4273c
Author: SeongJae Park <sj38.park@gmail.com>
Date:   Mon Sep 4 02:49:01 2023 +0000

    _damon_sysfs: Support DAMOS apply intervals

    Signed-off-by: SeongJae Park <sj38.park@gmail.com>

 _damon_sysfs.py                | 4 +++-
 tests/unit/test_damon_sysfs.py | 1 +
 2 files changed, 4 insertions(+), 1 deletion(-)

[honggyukim]

It looks apply_interval_us is newly added, but I need to investigate what it is.

[honggyukim]

The thing is that my kernel doesn't have apply_interval_us inside sysfs.

$ ls /sys/kernel/mm/damon/admin/kdamonds/0/contexts/0/schemes/0/
access_pattern  action  filters  quotas  stats  tried_regions  watermarks

$ ls /sys/kernel/mm/damon/admin/kdamonds/0/contexts/0/schemes/0/apply_interval_us
ls: cannot access '/sys/kernel/mm/damon/admin/kdamonds/0/contexts/0/schemes/0/apply_interval_us': No such file or directory

[honggyukim]

It looks apply_interval_us comes from https://git.kernel.org/pub/scm/linux/kernel/git/sj/linux.git/commit/?h=damon/next&id=b4075b3601ceccc383ab32d8b06b7ad8db0dbc3d, which is not merged into the mainline.

We might have to keep the backward compatibility with and without this change.

[sj-aws]

Thank you for this report, Honggyu! Also thank you for further deeply investigating the root cause. As you found, this is due to the under-development feature. We're developing a feature called DAMOS apply interval, which will make DAMOS be able to be applied regardless of the aggregation interval. It's still in only the damon/next tree, and recently damo has updated to support it. However, I forgot adding check of the availability of the feature on running kernel.

I also noticed DAMON functionality tests failing on latest >=6.1 kernels. I guess this was the reason.

I just implemented the check, confirmed it working, and pushed: b5ae1c1

Please let me know if it doesn't work for you.

[honggyukim]

Hi SeongJae,

Thanks for the quick fix. I've tested it on my home machine and see that the problem is fixed.

I will test it in the office tomorrow again, then close this issue. Thanks!

[honggyukim]

I've just confirmed that b5ae1c1 fixes the problem. Thanks very much!