linux-kernel - Re: [RFC PATCH 7/9] mm/damon/core: set damos_filter default allowance behavior based on installed filters

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Message-Id: <20250227002913.19359-1-sj@kernel.org>
Date: Wed, 26 Feb 2025 16:29:13 -0800
From: SeongJae Park <sj@...nel.org>
To: SeongJae Park <sj@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	damon@...ts.linux.dev,
	kernel-team@...a.com,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [RFC PATCH 7/9] mm/damon/core: set damos_filter default allowance behavior based on installed filters

On Thu, 20 Feb 2025 11:35:07 -0800 SeongJae Park <sj@...nel.org> wrote:

> Decide whether to allow or reject by default on core and opertions layer
> handled filters evaluation stages, based on the last-installed filter's
> behavior.  It is the opposite of the last installed filter's behavior.
> If there is any operations layer handled filters, core layer handled
> filters stage keeps allowing as the default behavior, since the last
> filter of core layer handled filters in the case is not really the last
> filter of the entire filtering stage.

The last sentence describing behavior is not really implemented with this
commit.  See below.

> 
> Signed-off-by: SeongJae Park <sj@...nel.org>
> ---
>  mm/damon/core.c | 31 +++++++++++++++++++++++++++++--
>  1 file changed, 29 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/damon/core.c b/mm/damon/core.c
> index 78126a5145fd..9744ab9ca5c5 100644
> --- a/mm/damon/core.c
> +++ b/mm/damon/core.c
> @@ -864,6 +864,29 @@ static int damos_commit_ops_filters(struct damos *dst, struct damos *src)
>  	return 0;
>  }
>  
> +/**
> + * damos_filters_default_reject() - decide whether to reject memory that didn't
> + *				    match with any given filter.
> + * @filters:	Given DAMOS filters of a group.
> + */
> +static bool damos_filters_default_reject(struct list_head *filters)
> +{
> +	struct damos_filter *last_filter;
> +
> +	if (list_empty(filters))
> +		return false;
> +	last_filter = list_last_entry(filters, struct damos_filter, list);
> +	return last_filter->allow;
> +}
> +
> +static void damos_set_filters_default_reject(struct damos *s)
> +{
> +	s->core_filters_default_reject =
> +		damos_filters_default_reject(&s->filters);
> +	s->ops_filters_default_reject =
> +		damos_filters_default_reject(&s->ops_filters);
> +}

->core_filters_default_reject should be 'false' if s->ops_filters is not empty,
since the last one of ->ops_filters is not the real last filter.  But this code
is not handling the case.

I will fix this in the next revision.


Thanks,
SJ

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