From patchwork Fri Nov 5 20:47:03 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Andrew Morton X-Patchwork-Id: 12605871 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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 21B41C433EF for ; Fri, 5 Nov 2021 20:47:07 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id CB15360240 for ; Fri, 5 Nov 2021 20:47:06 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org CB15360240 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux-foundation.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvack.org Received: by kanga.kvack.org (Postfix) id 629B79400E5; Fri, 5 Nov 2021 16:47:06 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 5D9289400C1; Fri, 5 Nov 2021 16:47:06 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 4A1F69400E5; Fri, 5 Nov 2021 16:47:06 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0140.hostedemail.com [216.40.44.140]) by kanga.kvack.org (Postfix) with ESMTP id 357359400C1 for ; Fri, 5 Nov 2021 16:47:06 -0400 (EDT) Received: from smtpin22.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id E2B301819609D for ; Fri, 5 Nov 2021 20:47:05 +0000 (UTC) X-FDA: 78776061210.22.5596F40 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf15.hostedemail.com (Postfix) with ESMTP id 7955ED0000A8 for ; Fri, 5 Nov 2021 20:46:54 +0000 (UTC) Received: by mail.kernel.org (Postfix) with ESMTPSA id 2C82B60174; Fri, 5 Nov 2021 20:47:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1636145224; bh=M5GLFS5tB6wqOdP/GMOSX3S4NFfMPBQx++niQv3FIyA=; h=Date:From:To:Subject:In-Reply-To:From; b=XryPuswlY1CW1XvtarrtsIxBRptDdiQfuMugTb0HeHwgKL/y1QFv4A46fxuqbr8Sc iEik3a6cnbpus0cUgExybBWYShzw4tnwVK9ttbOzgZQaQTU4d5O3DAUHjalVgrftEo me2zj5buzdLjTWA2cjlPHqe7x1fRqAGnQO7MRW+w= Date: Fri, 05 Nov 2021 13:47:03 -0700 From: Andrew Morton To: akpm@linux-foundation.org, amit@kernel.org, benh@kernel.crashing.org, brendanhiggins@google.com, corbet@lwn.net, david@redhat.com, dwmw@amazon.com, elver@google.com, foersleo@amazon.de, gthelen@google.com, Jonathan.Cameron@huawei.com, linux-mm@kvack.org, markubo@amazon.de, mm-commits@vger.kernel.org, rientjes@google.com, shakeelb@google.com, shuah@kernel.org, sj@kernel.org, torvalds@linux-foundation.org Subject: [patch 236/262] Docs/DAMON: document physical memory monitoring support Message-ID: <20211105204703.vXHvH1Bl-%akpm@linux-foundation.org> In-Reply-To: <20211105133408.cccbb98b71a77d5e8430aba1@linux-foundation.org> User-Agent: s-nail v14.8.16 MIME-Version: 1.0 Authentication-Results: imf15.hostedemail.com; dkim=pass header.d=linux-foundation.org header.s=korg header.b=XryPuswl; dmarc=none; spf=pass (imf15.hostedemail.com: domain of akpm@linux-foundation.org designates 198.145.29.99 as permitted sender) smtp.mailfrom=akpm@linux-foundation.org X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 7955ED0000A8 X-Stat-Signature: 35bqen6ppmp68p4t5k63d9waxkw1hm19 X-HE-Tag: 1636145214-659616 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: From: SeongJae Park Subject: Docs/DAMON: document physical memory monitoring support This commit updates the DAMON documents for the physical memory address space monitoring support. Link: https://lkml.kernel.org/r/20211012205711.29216-8-sj@kernel.org Signed-off-by: SeongJae Park Cc: Amit Shah Cc: Benjamin Herrenschmidt Cc: Brendan Higgins Cc: David Hildenbrand Cc: David Rienjes Cc: David Woodhouse Cc: Greg Thelen Cc: Jonathan Cameron Cc: Jonathan Corbet Cc: Leonard Foerster Cc: Marco Elver Cc: Markus Boehme Cc: Shakeel Butt Cc: Shuah Khan Signed-off-by: Andrew Morton --- Documentation/admin-guide/mm/damon/usage.rst | 25 +++++++++++--- Documentation/vm/damon/design.rst | 29 ++++++++++------- Documentation/vm/damon/faq.rst | 5 +- 3 files changed, 40 insertions(+), 19 deletions(-) --- a/Documentation/admin-guide/mm/damon/usage.rst~docs-damon-document-physical-memory-monitoring-support +++ a/Documentation/admin-guide/mm/damon/usage.rst @@ -10,15 +10,16 @@ DAMON provides below three interfaces fo This is for privileged people such as system administrators who want a just-working human-friendly interface. Using this, users can use the DAMON’s major features in a human-friendly way. It may not be highly tuned for - special cases, though. It supports only virtual address spaces monitoring. + special cases, though. It supports both virtual and physical address spaces + monitoring. - *debugfs interface.* This is for privileged user space programmers who want more optimized use of DAMON. Using this, users can use DAMON’s major features by reading from and writing to special debugfs files. Therefore, you can write and use your personalized DAMON debugfs wrapper programs that reads/writes the debugfs files instead of you. The DAMON user space tool is also a reference - implementation of such programs. It supports only virtual address spaces - monitoring. + implementation of such programs. It supports both virtual and physical + address spaces monitoring. - *Kernel Space Programming Interface.* This is for kernel space programmers. Using this, users can utilize every feature of DAMON most flexibly and efficiently by writing kernel space @@ -72,20 +73,34 @@ check it again:: # cat target_ids 42 4242 +Users can also monitor the physical memory address space of the system by +writing a special keyword, "``paddr\n``" to the file. Because physical address +space monitoring doesn't support multiple targets, reading the file will show a +fake value, ``42``, as below:: + + # cd /damon + # echo paddr > target_ids + # cat target_ids + 42 + Note that setting the target ids doesn't start the monitoring. Initial Monitoring Target Regions --------------------------------- -In case of the debugfs based monitoring, DAMON automatically sets and updates -the monitoring target regions so that entire memory mappings of target +In case of the virtual address space monitoring, DAMON automatically sets and +updates the monitoring target regions so that entire memory mappings of target processes can be covered. However, users can want to limit the monitoring region to specific address ranges, such as the heap, the stack, or specific file-mapped area. Or, some users can know the initial access pattern of their workloads and therefore want to set optimal initial regions for the 'adaptive regions adjustment'. +In contrast, DAMON do not automatically sets and updates the monitoring target +regions in case of physical memory monitoring. Therefore, users should set the +monitoring target regions by themselves. + In such cases, users can explicitly set the initial monitoring target regions as they want, by writing proper values to the ``init_regions`` file. Each line of the input should represent one region in below form.:: --- a/Documentation/vm/damon/design.rst~docs-damon-document-physical-memory-monitoring-support +++ a/Documentation/vm/damon/design.rst @@ -35,13 +35,17 @@ two parts: 1. Identification of the monitoring target address range for the address space. 2. Access check of specific address range in the target space. -DAMON currently provides the implementation of the primitives for only the -virtual address spaces. Below two subsections describe how it works. +DAMON currently provides the implementations of the primitives for the physical +and virtual address spaces. Below two subsections describe how those work. VMA-based Target Address Range Construction ------------------------------------------- +This is only for the virtual address space primitives implementation. That for +the physical address space simply asks users to manually set the monitoring +target address ranges. + Only small parts in the super-huge virtual address space of the processes are mapped to the physical memory and accessed. Thus, tracking the unmapped address regions is just wasteful. However, because DAMON can deal with some @@ -71,15 +75,18 @@ to make a reasonable trade-off. Below s PTE Accessed-bit Based Access Check ----------------------------------- -The implementation for the virtual address space uses PTE Accessed-bit for -basic access checks. It finds the relevant PTE Accessed bit from the address -by walking the page table for the target task of the address. In this way, the -implementation finds and clears the bit for next sampling target address and -checks whether the bit set again after one sampling period. This could disturb -other kernel subsystems using the Accessed bits, namely Idle page tracking and -the reclaim logic. To avoid such disturbances, DAMON makes it mutually -exclusive with Idle page tracking and uses ``PG_idle`` and ``PG_young`` page -flags to solve the conflict with the reclaim logic, as Idle page tracking does. +Both of the implementations for physical and virtual address spaces use PTE +Accessed-bit for basic access checks. Only one difference is the way of +finding the relevant PTE Accessed bit(s) from the address. While the +implementation for the virtual address walks the page table for the target task +of the address, the implementation for the physical address walks every page +table having a mapping to the address. In this way, the implementations find +and clear the bit(s) for next sampling target address and checks whether the +bit(s) set again after one sampling period. This could disturb other kernel +subsystems using the Accessed bits, namely Idle page tracking and the reclaim +logic. To avoid such disturbances, DAMON makes it mutually exclusive with Idle +page tracking and uses ``PG_idle`` and ``PG_young`` page flags to solve the +conflict with the reclaim logic, as Idle page tracking does. Address Space Independent Core Mechanisms --- a/Documentation/vm/damon/faq.rst~docs-damon-document-physical-memory-monitoring-support +++ a/Documentation/vm/damon/faq.rst @@ -36,10 +36,9 @@ constructions and actual access checks c DAMON core by the users. In this way, DAMON users can monitor any address space with any access check technique. -Nonetheless, DAMON provides vma tracking and PTE Accessed bit check based +Nonetheless, DAMON provides vma/rmap tracking and PTE Accessed bit check based implementations of the address space dependent functions for the virtual memory -by default, for a reference and convenient use. In near future, we will -provide those for physical memory address space. +and the physical memory by default, for a reference and convenient use. Can I simply monitor page granularity?