linux-kernel - Re: [PATCH v31 07/13] mm/damon: Implement a debugfs-based user space interface

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Message-ID: <CALvZod7gLSCqqYVR50F9-8DxG=gRL4seiHAqvSsr3A6U6cvjig@mail.gmail.com>
Date:   Thu, 24 Jun 2021 07:52:59 -0700
From:   Shakeel Butt <shakeelb@...gle.com>
To:     SeongJae Park <sj38.park@...il.com>
Cc:     SeongJae Park <sjpark@...zon.de>, Jonathan.Cameron@...wei.com,
        acme@...nel.org, alexander.shishkin@...ux.intel.com,
        amit@...nel.org, benh@...nel.crashing.org,
        Brendan Higgins <brendanhiggins@...gle.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@...ah.com,
        Greg Thelen <gthelen@...gle.com>, guoju.fgj@...baba-inc.com,
        jgowans@...zon.com, Mel Gorman <mgorman@...e.de>, mheyne@...zon.de,
        Minchan Kim <minchan@...nel.org>,
        Ingo Molnar <mingo@...hat.com>, namhyung@...nel.org,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Rik van Riel <riel@...riel.com>,
        David Rientjes <rientjes@...gle.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mike Rapoport <rppt@...nel.org>, Shuah Khan <shuah@...nel.org>,
        sieberf@...zon.com, snu@...le79.org,
        Vlastimil Babka <vbabka@...e.cz>,
        Vladimir Davydov <vdavydov.dev@...il.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: [PATCH v31 07/13] mm/damon: Implement a debugfs-based user space interface

On Thu, Jun 24, 2021 at 3:26 AM SeongJae Park <sj38.park@...il.com> wrote:
>
[...]
> >
> > The high level comment I have for this patch is the layering of pid
> > reference counting. The dbgfs should treat the targets as abstract
> > objects and vaddr should handle the reference counting of pids. More
> > specifically move find_get_pid from dbgfs to vaddr and to add an
> > interface to the primitive for set_targets.
> >
> > At the moment, the pid reference is taken in dbgfs and put in vaddr.
> > This will be the source of bugs in future.
>
> Good point, and agreed on the problem.  But, I'd like to move 'put_pid()' to
> dbgfs, because I think that would let extending the dbgfs user interface to
> pidfd a little bit simpler.  Also, I think that would be easier to use for
> in-kernel programming interface usages.  If you disagree, please feel free to
> let me know.
>

I was thinking of removing targetid_is_pid() checks. Anyways this is
not something we can not change later, so I will let you decide which
direction you want to take.