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Date:   Tue, 3 Oct 2023 20:50:22 -0400
From:   Steven Rostedt <rostedt@goodmis.org>
To:     SeongJae Park <sj@kernel.org>
Cc:     Andrew Morton <akpm@linux-foundation.org>, damon@lists.linux.dev,
        linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH RESEND v2 1/2] mm/damon/core: add a tracepoint for damos
 apply target regions
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In-Reply-To: <20230913022050.2109-2-sj@kernel.org>
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        <20230913022050.2109-2-sj@kernel.org>
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On Wed, 13 Sep 2023 02:20:49 +0000
SeongJae Park <sj@kernel.org> wrote:

> DAMON provides damon_aggregated tracepoint, which exposes details of
> each region and its access monitoring results.  It is useful for
> getting whole monitoring results, e.g., for recording purposes.
> 
> For investigations of DAMOS, DAMON Sysfs interface provides DAMOS
> statistics and tried_regions directory.  But, those provides only
> statistics and snapshots.  If the scheme is frequently applied and if
> the user needs to know every detail of DAMOS behavior, the
> snapshot-based interface could be insufficient and expensive.
> 
> As a last resort, userspace users need to record the all monitoring
> results via damon_aggregated tracepoint and simulate how DAMOS would
> worked.  It is unnecessarily complicated.  DAMON kernel API users,
> meanwhile, can do that easily via before_damos_apply() callback field of
> 'struct damon_callback', though.
> 
> Add a tracepoint that will be called just after before_damos_apply()
> callback for more convenient investigations of DAMOS.  The tracepoint
> exposes all details about each regions, similar to damon_aggregated
> tracepoint.
> 
> Please note that DAMOS is currently not only for memory management but
> also for query-like efficient monitoring results retrievals (when 'stat'
> action is used).  Until now, only statistics or snapshots were
> supported.  Addition of this tracepoint allows efficient full recording
> of DAMOS-based filtered monitoring results.
> 

From a tracing point of view.

Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>

-- Steve