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Tue, 09 Jun 2020 10:07:22 -0400 X-MC-Unique: 0ocdvd3tP_eQPi4z7Gd6dQ-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id C386457096; Tue, 9 Jun 2020 14:07:13 +0000 (UTC) Received: from [10.36.114.103] (ovpn-114-103.ams2.redhat.com [10.36.114.103]) by smtp.corp.redhat.com (Postfix) with ESMTP id C140C10013C1; Tue, 9 Jun 2020 14:07:01 +0000 (UTC) Subject: Re: [RFC v11 3/8] mm/damon: Implement data access monitoring-based operation schemes To: SeongJae Park Cc: akpm@linux-foundation.org, SeongJae Park , Jonathan.Cameron@Huawei.com, aarcange@redhat.com, acme@kernel.org, alexander.shishkin@linux.intel.com, amit@kernel.org, benh@kernel.crashing.org, brendan.d.gregg@gmail.com, brendanhiggins@google.com, cai@lca.pw, colin.king@canonical.com, corbet@lwn.net, dwmw@amazon.com, foersleo@amazon.de, irogers@google.com, jolsa@redhat.com, kirill@shutemov.name, mark.rutland@arm.com, mgorman@suse.de, minchan@kernel.org, mingo@redhat.com, namhyung@kernel.org, peterz@infradead.org, rdunlap@infradead.org, riel@surriel.com, rientjes@google.com, rostedt@goodmis.org, sblbir@amazon.com, shakeelb@google.com, shuah@kernel.org, sj38.park@gmail.com, snu@amazon.de, vbabka@suse.cz, vdavydov.dev@gmail.com, yang.shi@linux.alibaba.com, ying.huang@intel.com, linux-damon@amazon.com, linux-mm@kvack.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org References: <20200609091725.15859-1-sjpark@amazon.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 MIME-Version: 1.0 In-Reply-To: <20200609091725.15859-1-sjpark@amazon.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Rspamd-Queue-Id: C9704184E663F X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam04 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 09.06.20 11:17, SeongJae Park wrote: > On Tue, 9 Jun 2020 10:47:45 +0200 David Hildenbrand wrote: > >> On 09.06.20 08:53, SeongJae Park wrote: >>> From: SeongJae Park >>> >>> In many cases, users might use DAMON for simple data access aware >>> memory management optimizations such as applying an operation scheme to >>> a memory region of a specific size having a specific access frequency >>> for a specific time. For example, "page out a memory region larger than >>> 100 MiB but having a low access frequency more than 10 minutes", or "Use >>> THP for a memory region larger than 2 MiB having a high access frequency >>> for more than 2 seconds". >>> >>> To minimize users from spending their time for implementation of such >>> simple data access monitoring-based operation schemes, this commit makes >>> DAMON to handle such schemes directly. With this commit, users can >>> simply specify their desired schemes to DAMON. >> >> What would be the alternative? How would a solution where these policies >> are handled by user space (or inside an application?) look like? > > Most simple form of the altermative solution would be doing offline data access > pattern profiling using DAMON and modifying the application source code or > system configuration based on the profiling results. > > More automated alternative solution would be a daemon constructed with two > modules: > > - monitor: monitors the data access pattern of the workload via the DAMON > debugfs interface > - memory manager: based on the monitoring result, make appropriate memory > management changes via mlock(), madvise(), sysctl, etc. > > The daemon would be able to run inside the application process as a thread, or > outside as a standalone process. If the daemon could not run inside the > application process, the memory management changes it could make would be > further limited, though, as mlock() and madvise() would not be available. The > madvise_process(), which is already merged in the next tree, would be helpful > in this case. > >>> >>> Each of the schemes is composed with conditions for filtering of the >>> target memory regions and desired memory management action for the >>> target. Specifically, the format is:: >>> >>> >>> >>> The filtering conditions are size of memory region, number of accesses >>> to the region monitored by DAMON, and the age of the region. The age of >>> region is incremented periodically but reset when its addresses or >>> access frequency has significantly changed or the action of a scheme was >>> applied. For the action, current implementation supports only a few of >>> madvise() hints, ``MADV_WILLNEED``, ``MADV_COLD``, ``MADV_PAGEOUT``, >>> ``MADV_HUGEPAGE``, and ``MADV_NOHUGEPAGE``. >> >> I am missing some important information. Is this specified for *all* >> user space processes? Or how is this configured? What are examples? >> >> E.g., messing with ``MADV_HUGEPAGE`` vs. ``MADV_NOHUGEPAGE`` of random >> applications can change the behavior/break these applications. (e.g., if >> userfaultfd is getting used and the applciation explicitly sets >> MADV_NOHUGEPAGE). > > Only monitoring target processes will be applied. The monitoring target > processes can be specified by writing the process ids to 'pids' debugfs file or > constructing the 'struct damon_ctx' via the programming interface. > > I will refine the commit message to make the points clearer, in the next spin. Understood, so a process configures damon to only modify its mappings. thanks for clarifying! This makes exposing the do_madvise() look less dangerous. -- Thanks, David / dhildenb