From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9254AC7EE2C for ; Thu, 25 May 2023 21:43:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241931AbjEYVn3 (ORCPT ); Thu, 25 May 2023 17:43:29 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46702 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241926AbjEYVn2 (ORCPT ); Thu, 25 May 2023 17:43:28 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D9BC512C; Thu, 25 May 2023 14:43:26 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id BA7B164B75; Thu, 25 May 2023 21:43:26 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9C31EC4339E; Thu, 25 May 2023 21:43:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1685051006; bh=APr09IDiXGykzuGGa19YHF7doztMwWo2QuV04whzSE8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=nzbBk6KCaeEKjgaCqUIVU5hTiLijuoQ2H2aJfAUzxi/UVr0w7ei8EnEamotAgKXfL 1JF/RgO5UylZl9FlBIpP399R6mpJfXhfU8jx72dyC0YDzfWvAjkDaf22nyQ9VIRqeY Xc1e1uEfUPDeYFysPQ5t9qDZVJhWXzg5djp9FRE5fSGQuimSe0YWEqmJwuoR1rQPUG G6i6YnbO3iJYJqgyTvJVVAByL5/4lUEU039yAGDyAX0TIFjzqJFJatQ/no1KeLwdNx G84vkoXyWM1gRPfQVIfhW57qQ2wnQ8HyVM7PXxMOYP2YxHQXN6+/hlIyR+gXywy4Pt niR+/fxAA9vmw== From: SeongJae Park To: Andrew Morton Cc: SeongJae Park , Jonathan Corbet , damon@lists.linux.dev, linux-mm@kvack.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH 07/10] Docs/mm/damon/design: add sections for basic parts of DAMOS Date: Thu, 25 May 2023 21:43:11 +0000 Message-Id: <20230525214314.5204-8-sj@kernel.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20230525214314.5204-1-sj@kernel.org> References: <20230525214314.5204-1-sj@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org DAMOS is an important part of DAMON, but the design doc is not covering it. Add sections for covering the basic part of DAMOS. Signed-off-by: SeongJae Park --- Documentation/mm/damon/design.rst | 70 +++++++++++++++++++++++++++++++ 1 file changed, 70 insertions(+) diff --git a/Documentation/mm/damon/design.rst b/Documentation/mm/damon/design.rst index 41abd0430dd7..9f9253529c3d 100644 --- a/Documentation/mm/damon/design.rst +++ b/Documentation/mm/damon/design.rst @@ -202,3 +202,73 @@ monitoring operations to check dynamic changes including memory mapping changes and applies it to monitoring operations-related data structures such as the abstracted monitoring target memory area only for each of a user-specified time interval (``update interval``). + + +Operation Schemes +----------------- + +One common purpose of data access monitoring is access-aware system efficiency +optimizations. For example, + + paging out memory regions that are not accessed for more than two minutes + +or + + using THP for memory regions that are larger than 2 MiB and showing a high + access frequency for more than one minute. + +One straightforward approach for such schemes would be profile-guided +optimizations. That is, getting data access monitoring results of the +workloads or the system using DAMON, finding memory regions of special +characteristics by profiling the monitoring results, and making system +operation changes for the regions. The changes could be made by modifying or +providing advice to the software (the application and/or the kernel), or +reconfiguring the hardware. Both offline and online approaches could be +available. + +Among those, providing advice to the kernel at runtime would be flexible and +effective, and therefore widely be used. However, implementing such schemes +could impose unnecessary redundancy and inefficiency. The profiling could be +redundant if the type of interest is common. Exchanging the information +including monitoring results and operation advice between kernel and user +spaces could be inefficient. + +To allow users to reduce such redundancy and inefficiencies by offloading the +works, DAMON provides a feature called Data Access Monitoring-based Operation +Schemes (DAMOS). It lets users specify their desired schemes at a high +level. For such specifications, DAMON starts monitoring, finds regions having +the access pattern of interest, and applies the user-desired operation actions +to the regions as soon as found. + + +Operation Action +~~~~~~~~~~~~~~~~ + +The management action that the users desire to apply to the regions of their +interest. For example, paging out, prioritizing for next reclamation victim +selection, advising ``khugepaged`` to collapse or split, or doing nothing but +collecting statistics of the regions. + +The list of supported actions is defined in DAMOS, but the implementation of +each action is in the DAMON operations set layer because the implementation +normally depends on the monitoring target address space. For example, the code +for paging specific virtual address ranges out would be different from that for +physical address ranges. And the monitoring operations implementation sets are +not mandated to support all actions of the list. Hence, the availability of +specific DAMOS action depends on what operations set is selected to be used +together. + +Applying an action to a region is considered as changing the region's +characteristics. Hence, DAMOS resets the age of regions when an action is +applied to those. + + +Target Access Pattern +~~~~~~~~~~~~~~~~~~~~~ + +The access pattern of the schemes' interest. The patterns are constructed with +the properties that DAMON's monitoring results provide, specifically the size, +the access frequency, and the age. Users can describe their access pattern of +interest by setting minimum and maximum values of the three properties. If a +region's three properties are in the ranges, DAMOS classifies it as one of the +regions that the scheme is having an interest in. -- 2.25.1