linux-kernel - Re: [RFC PATCH 2/2] mm/damon/debugfs: Support multiple contexts

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Date:   Wed, 16 Sep 2020 09:11:18 -0700
From:   Shakeel Butt <shakeelb@...gle.com>
To:     SeongJae Park <sjpark@...zon.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        SeongJae Park <sjpark@...zon.de>, Jonathan.Cameron@...wei.com,
        Andrea Arcangeli <aarcange@...hat.com>, acme@...nel.org,
        alexander.shishkin@...ux.intel.com, amit@...nel.org,
        benh@...nel.crashing.org, brendan.d.gregg@...il.com,
        Brendan Higgins <brendanhiggins@...gle.com>,
        Qian Cai <cai@....pw>,
        Colin Ian King <colin.king@...onical.com>,
        Jonathan Corbet <corbet@....net>,
        David Hildenbrand <david@...hat.com>, dwmw@...zon.com,
        Marco Elver <elver@...gle.com>, "Du, Fan" <fan.du@...el.com>,
        foersleo@...zon.de, Greg Thelen <gthelen@...gle.com>,
        Ian Rogers <irogers@...gle.com>, jolsa@...hat.com,
        "Kirill A. Shutemov" <kirill@...temov.name>, mark.rutland@....com,
        Mel Gorman <mgorman@...e.de>, Minchan Kim <minchan@...nel.org>,
        Ingo Molnar <mingo@...hat.com>, namhyung@...nel.org,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Rik van Riel <riel@...riel.com>,
        David Rientjes <rientjes@...gle.com>,
        Steven Rostedt <rostedt@...dmis.org>, rppt@...nel.org,
        sblbir@...zon.com, shuah@...nel.org, sj38.park@...il.com,
        snu@...zon.de, Vlastimil Babka <vbabka@...e.cz>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Yang Shi <yang.shi@...ux.alibaba.com>,
        Huang Ying <ying.huang@...el.com>, zgf574564920@...il.com,
        linux-damon@...zon.com, Linux MM <linux-mm@...ck.org>,
        linux-doc@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 2/2] mm/damon/debugfs: Support multiple contexts

On Tue, Sep 15, 2020 at 11:03 AM SeongJae Park <sjpark@...zon.com> wrote:
>
> From: SeongJae Park <sjpark@...zon.de>
>
> DAMON allows the programming interface users to run monitoring with
> multiple contexts.  This could be useful in some cases.  For example, if
> someone want to do highly accurate monitoring and lots of CPUs are
> available, splitting the monitoring target regions into multiple small
> regions and allocating context (monitoring thread) to each small region
> could be helpful.  Or, someone could need to monitor different types of
> address spaces simultaneously.
>
> However, it's impossible from the user space because the DAMON debugfs
> interface supports only single context.  This commit makes it available
> by implementing 'nr_contexts' debugfs file.
>
> Users can pass the number (N) of contexts they want to use to the file.

Why not just mkdir which will create a new context?

> Then, N folders having name of 'ctx<1-(N-1)>' are created in the DAMON
> debugfs dir.  Each of the directory is associated with the contexts and
> contains the the files for context setting (attrs, init_regions, record,
> schemes, and target_ids).

Also instead of naming the kthread with context number why not give
the kthread pids through attrs (or new interface) and the admin can
move those kthreads to the cgroup they want to charge against?

> The first context related files are still in
> the DAMON debugfs root directory, though.
>
> Signed-off-by: SeongJae Park <sjpark@...zon.de>
> ---