linux-kernel - Re: [PATCH v23 01/15] mm: Introduce Data Access MONitor (DAMON)

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Date:   Wed, 23 Dec 2020 14:49:57 -0800
From:   Shakeel Butt <shakeelb@...gle.com>
To:     SeongJae Park <sjpark@...zon.com>
Cc:     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 <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>,
        Mike Rapoport <rppt@...nel.org>, sblbir@...zon.com,
        Shuah Khan <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: [PATCH v23 01/15] mm: Introduce Data Access MONitor (DAMON)

On Wed, Dec 23, 2020 at 8:34 AM SeongJae Park <sjpark@...zon.com> wrote:
[snip]
> > Overall the patch looks good to me. Two concerns I have are if we
> > should damon_callback here or with the real user and the regions part
> > of primitive abstraction. For the first one, I don't have any strong
> > opinion but for the second one I do.
>
> I'd like to keep 'damon_callback' part here, to let API users know how the
> monitoring result will be available to them.
>
> For the 'regions' part, I will rename relevant things as below in the next
> version, to reduce any confusion.
>
> init_target_regions() -> init()
> update_target_regions() -> update()
> regions_update_interval -> update_interval
> last_regions_update -> last_update
>
> >
> > More specifically the question is if sampling and adaptive region
> > adjustment are general enough to be part of core monitoring context?
> > Can you give an example of a different primitive/use-case where these
> > would be beneficial.
>
> I think all adress spaces having some spatial locality and monitoring requests
> that need to have upper-bound overhead and best-effort accuracy could get
> benefit from it.  The primitives targetting 'virtual address spaces' and the
> 'physical address space' clearly showed the benefit.

I am still not much convinced on the 'physical address space' use-case
or the way you are presenting it. Anyways I think we start with what
you have and if in future there is a use-case where regions adjustment
does not make sense, we can change it then.