From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on archive.lwn.net X-Spam-Level: X-Spam-Status: No, score=-5.8 required=5.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, RCVD_IN_DNSWL_HI,SPF_HELO_NONE,SPF_NONE autolearn=ham autolearn_force=no version=3.4.2 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by archive.lwn.net (Postfix) with ESMTP id C8C3D7DBEB for ; Mon, 5 Aug 2019 17:05:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729941AbfHERFV (ORCPT ); Mon, 5 Aug 2019 13:05:21 -0400 Received: from mail-pl1-f194.google.com ([209.85.214.194]:36235 "EHLO mail-pl1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729566AbfHERFU (ORCPT ); Mon, 5 Aug 2019 13:05:20 -0400 Received: by mail-pl1-f194.google.com with SMTP id k8so36731845plt.3 for ; Mon, 05 Aug 2019 10:05:20 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=joelfernandes.org; s=google; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=EpW+/zsfaWUWqnp/CzJ8iSD2ZsdUd34jJeLFlQmjMJk=; b=hgyWzkgSkWIkAiyvGZ+G+xjb4IZCoTupPLFm8KMlB2b4hKbMxa1b+uIr1iRdua+wqE QC4A3wju5EZMPMzUeRrpvG6gxy5MEYfQ82W1fGN8SHtXC5yuCxMcBGlIpCV6ZH3OP4zQ UMkuRWp/Da9107v0m9+9yab3KvcgH65HHQUcA= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=EpW+/zsfaWUWqnp/CzJ8iSD2ZsdUd34jJeLFlQmjMJk=; b=Sa+PtDJu2HhYc3IsgVjkRXOvsDLSb5/lnarDlmiqc+qx7Og/77z0ubwSXtmR7pNNTy 0FJv6RPZYQarLDQw+03h3EhsDIkGR+U7rJjXiIZUv8ZqxyKPwDLJIibTGft8Pc48nKrC 96NM0k+ofjUPpCdHHhyQX1ipuqXNQaLIi8yOVSX/lWmGo2oQk3GMIy4fwKtBRT6qj93+ 7BMFxj761aSwz2QwDeDaeOl4jfr60f7zmtPcVy37pje+1m28uc6Ad1tkEe1OrsK0iOrv XjLpblu0AAIXNXrXTsBnT6d7cKEczWbX9HLf3AnVdfpmA1pkg7TElatiP65R+czV5w/l lWwQ== X-Gm-Message-State: APjAAAVxtkGvQPWoP3mJxbeW0SzmFF95Me770BrxoFJ989wu8VDxeEyU A7aRzw8IS2f2VBg86WsTuCc= X-Google-Smtp-Source: APXvYqza5nQrNDdoUqGT6kyvYnC1EmmsZrzblP42jhwdV0CyAlqgihwZyUT70kUG+iUloT382Cjx7g== X-Received: by 2002:a17:902:9a95:: with SMTP id w21mr61715428plp.126.1565024719760; Mon, 05 Aug 2019 10:05:19 -0700 (PDT) Received: from joelaf.cam.corp.google.com ([2620:15c:6:12:9c46:e0da:efbf:69cc]) by smtp.gmail.com with ESMTPSA id p23sm89832934pfn.10.2019.08.05.10.05.16 (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Mon, 05 Aug 2019 10:05:19 -0700 (PDT) From: "Joel Fernandes (Google)" To: linux-kernel@vger.kernel.org Cc: "Joel Fernandes (Google)" , Mike Rapoport , Sandeep Patil , Alexey Dobriyan , Andrew Morton , Borislav Petkov , Brendan Gregg , Catalin Marinas , Christian Hansen , dancol@google.com, fmayer@google.com, "H. Peter Anvin" , Ingo Molnar , joelaf@google.com, Jonathan Corbet , Kees Cook , kernel-team@android.com, linux-api@vger.kernel.org, linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, Michal Hocko , minchan@kernel.org, namhyung@google.com, paulmck@linux.ibm.com, Robin Murphy , Roman Gushchin , Stephen Rothwell , surenb@google.com, Thomas Gleixner , tkjos@google.com, Vladimir Davydov , Vlastimil Babka , Will Deacon Subject: [PATCH v4 5/5] doc: Update documentation for page_idle virtual address indexing Date: Mon, 5 Aug 2019 13:04:51 -0400 Message-Id: <20190805170451.26009-5-joel@joelfernandes.org> X-Mailer: git-send-email 2.22.0.770.g0f2c4a37fd-goog In-Reply-To: <20190805170451.26009-1-joel@joelfernandes.org> References: <20190805170451.26009-1-joel@joelfernandes.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org This patch updates the documentation with the new page_idle tracking feature which uses virtual address indexing. Reviewed-by: Mike Rapoport Reviewed-by: Sandeep Patil Signed-off-by: Joel Fernandes (Google) --- .../admin-guide/mm/idle_page_tracking.rst | 43 ++++++++++++++++--- 1 file changed, 36 insertions(+), 7 deletions(-) diff --git a/Documentation/admin-guide/mm/idle_page_tracking.rst b/Documentation/admin-guide/mm/idle_page_tracking.rst index df9394fb39c2..9eef32000f5e 100644 --- a/Documentation/admin-guide/mm/idle_page_tracking.rst +++ b/Documentation/admin-guide/mm/idle_page_tracking.rst @@ -19,10 +19,14 @@ It is enabled by CONFIG_IDLE_PAGE_TRACKING=y. User API ======== +There are 2 ways to access the idle page tracking API. One uses physical +address indexing, another uses a simpler virtual address indexing scheme. -The idle page tracking API is located at ``/sys/kernel/mm/page_idle``. -Currently, it consists of the only read-write file, -``/sys/kernel/mm/page_idle/bitmap``. +Physical address indexing +------------------------- +The idle page tracking API for physical address indexing using page frame +numbers (PFN) is located at ``/sys/kernel/mm/page_idle``. Currently, it +consists of the only read-write file, ``/sys/kernel/mm/page_idle/bitmap``. The file implements a bitmap where each bit corresponds to a memory page. The bitmap is represented by an array of 8-byte integers, and the page at PFN #i is @@ -74,6 +78,31 @@ See :ref:`Documentation/admin-guide/mm/pagemap.rst ` for more information about ``/proc/pid/pagemap``, ``/proc/kpageflags``, and ``/proc/kpagecgroup``. +Virtual address indexing +------------------------ +The idle page tracking API for virtual address indexing using virtual frame +numbers (VFN) for a process ```` is located at ``/proc//page_idle``. +It is a bitmap that follows the same semantics as +``/sys/kernel/mm/page_idle/bitmap`` except that it uses virtual instead of +physical frame numbers. + +This idle page tracking API does not deal with PFN so it does not require prior +lookups of ``pagemap``. This is an advantage on some systems where looking up +PFN is considered a security issue. Also in some cases, this interface could +be slightly more reliable to use than physical address indexing, since in +physical address indexing, address space changes can occur between reading the +``pagemap`` and reading the ``bitmap``, while in virtual address indexing, the +process's ``mmap_sem`` is held for the duration of the access. + +To estimate the amount of pages that are not used by a workload one should: + + 1. Mark all the workload's pages as idle by setting corresponding bits in + ``/proc//page_idle``. + + 2. Wait until the workload accesses its working set. + + 3. Read ``/proc//page_idle`` and count the number of bits set. + .. _impl_details: Implementation Details @@ -99,10 +128,10 @@ When a dirty page is written to swap or disk as a result of memory reclaim or exceeding the dirty memory limit, it is not marked referenced. The idle memory tracking feature adds a new page flag, the Idle flag. This flag -is set manually, by writing to ``/sys/kernel/mm/page_idle/bitmap`` (see the -:ref:`User API ` -section), and cleared automatically whenever a page is referenced as defined -above. +is set manually, by writing to ``/sys/kernel/mm/page_idle/bitmap`` for physical +addressing or by writing to ``/proc//page_idle`` for virtual +addressing (see the :ref:`User API ` section), and cleared +automatically whenever a page is referenced as defined above. When a page is marked idle, the Accessed bit must be cleared in all PTEs it is mapped to, otherwise we will not be able to detect accesses to the page coming -- 2.22.0.770.g0f2c4a37fd-goog