Re: [RFC PATCH v2 07/10] selftests/damon/_damon_sysfs: support pause file staging

[SeongJae Park <sj@kernel.org>]

On Wed, 18 Mar 2026 22:21:50 -0700 SeongJae Park <sj@kernel.org> wrote:

> DAMON test-purpose sysfs interface control Python module, _damon_sysfs,
> is not supporting the newly added pause file.  Add the support of the
> file, for future test and use of the feature.
> 
> Signed-off-by: SeongJae Park <sj@kernel.org>
> ---
>  tools/testing/selftests/damon/_damon_sysfs.py | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/testing/selftests/damon/_damon_sysfs.py b/tools/testing/selftests/damon/_damon_sysfs.py
> index 2b4df655d9fd0..120b96ecbd741 100644
> --- a/tools/testing/selftests/damon/_damon_sysfs.py
> +++ b/tools/testing/selftests/damon/_damon_sysfs.py
> @@ -604,10 +604,11 @@ class DamonCtx:
>      targets = None
>      schemes = None
>      kdamond = None
> +    pause = None
>      idx = None
>  
>      def __init__(self, ops='paddr', monitoring_attrs=DamonAttrs(), targets=[],
> -            schemes=[]):
> +            schemes=[], pause=False):

Sashiko comment
(https://sashiko.dev/#/patchset/20260319052157.99433-8-sj@kernel.org) and my
reply.

: Since this line is being modified, could the use of mutable default
: arguments for monitoring_attrs, targets, and schemes cause unintended
: state sharing between instances?
: 
: In Python, default arguments are evaluated exactly once at function
: definition time. If multiple DamonCtx objects are instantiated without
: explicitly providing these parameters, they will share the exact same
: object instances in memory.
: 
: When the constructor later executes self.monitoring_attrs.context = self,
: it overwrites the context reference of the shared object to point to the
: newest DamonCtx instance. If multiple contexts are staged concurrently
: relying on the default arguments, earlier contexts might inadvertently
: write their sysfs files into the directory of the last created context.
: 
: Would it be better to use None for the defaults and instantiate new objects
: inside the constructor?

Good points.  Orthogonal to this patch, though.  Also, there is no such use
case of this class to my best knowledge.  I will consider such change later,
though.


Thanks,
SJ

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