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From:   Shakeel Butt <shakeelb@google.com>
Date:   Wed, 30 Jun 2021 17:07:51 -0700
Message-ID: <CALvZod6jTB=L34gh2awfOH=+3jZ0DCxXPtmj7NO95DzfqJ_MGA@mail.gmail.com>
Subject: Re: [PATCH v32 03/13] mm/damon: Adaptively adjust regions
To:     SeongJae Park <sj38.park@gmail.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        SeongJae Park <sjpark@amazon.de>, Jonathan.Cameron@huawei.com,
        acme@kernel.org, alexander.shishkin@linux.intel.com,
        amit@kernel.org, benh@kernel.crashing.org,
        Brendan Higgins <brendanhiggins@google.com>,
        Jonathan Corbet <corbet@lwn.net>,
        David Hildenbrand <david@redhat.com>, dwmw@amazon.com,
        Marco Elver <elver@google.com>, "Du, Fan" <fan.du@intel.com>,
        foersleo@amazon.de, greg@kroah.com,
        Greg Thelen <gthelen@google.com>, guoju.fgj@alibaba-inc.com,
        jgowans@amazon.com, Mel Gorman <mgorman@suse.de>, mheyne@amazon.de,
        Minchan Kim <minchan@kernel.org>,
        Ingo Molnar <mingo@redhat.com>, namhyung@kernel.org,
        "Peter Zijlstra (Intel)" <peterz@infradead.org>,
        Rik van Riel <riel@surriel.com>,
        David Rientjes <rientjes@google.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Mike Rapoport <rppt@kernel.org>, Shuah Khan <shuah@kernel.org>,
        sieberf@amazon.com, snu@zelle79.org,
        Vlastimil Babka <vbabka@suse.cz>,
        Vladimir Davydov <vdavydov.dev@gmail.com>,
        zgf574564920@gmail.com, linux-damon@amazon.com,
        Linux MM <linux-mm@kvack.org>, linux-doc@vger.kernel.org,
        LKML <linux-kernel@vger.kernel.org>
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On Mon, Jun 28, 2021 at 6:34 AM SeongJae Park <sj38.park@gmail.com> wrote:
>
> From: SeongJae Park <sjpark@amazon.de>
>
> Even somehow the initial monitoring target regions are well constructed
> to fulfill the assumption (pages in same region have similar access
> frequencies), the data access pattern can be dynamically changed.  This
> will result in low monitoring quality.  To keep the assumption as much
> as possible, DAMON adaptively merges and splits each region based on
> their access frequency.
>
> For each ``aggregation interval``, it compares the access frequencies of
> adjacent regions and merges those if the frequency difference is small.
> Then, after it reports and clears the aggregated access frequency of
> each region, it splits each region into two or three regions if the
> total number of regions will not exceed the user-specified maximum
> number of regions after the split.
>
> In this way, DAMON provides its best-effort quality and minimal overhead
> while keeping the upper-bound overhead that users set.
>
> Signed-off-by: SeongJae Park <sjpark@amazon.de>
> Reviewed-by: Leonard Foerster <foersleo@amazon.de>
> Reviewed-by: Fernand Sieber <sieberf@amazon.com>

Acked-by: Shakeel Butt <shakeelb@google.com>