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 X-Spam-Level: X-Spam-Status: No, score=-9.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 90CFAC76190 for ; Fri, 26 Jul 2019 15:09:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 64DDD229F3 for ; Fri, 26 Jul 2019 15:09:00 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=joelfernandes.org header.i=@joelfernandes.org header.b="aHKVCn8Y" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728402AbfGZPI7 (ORCPT ); Fri, 26 Jul 2019 11:08:59 -0400 Received: from mail-pl1-f194.google.com ([209.85.214.194]:40274 "EHLO mail-pl1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728328AbfGZPI6 (ORCPT ); Fri, 26 Jul 2019 11:08:58 -0400 Received: by mail-pl1-f194.google.com with SMTP id a93so24828792pla.7 for ; Fri, 26 Jul 2019 08:08:57 -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=dWQZR/3W1JJGAqPUD7hTWyfWfaLoNTQhqklPLc/rCo0=; b=aHKVCn8Yp9k/O48xxeey02lLJNycfqq+nT8pu97tqLat8sXh6527ZcHjiLMjFGs8ZZ SzpXGhN97m6q7LoR5xxBb5fekgPrddIS2ckjFbLcS/b41a8DTKGviU3TjgY2guZy2wOV N7hTZrckEmKJ55qJ5XLQRPA1RD8Ilyo39Glr8= 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=dWQZR/3W1JJGAqPUD7hTWyfWfaLoNTQhqklPLc/rCo0=; b=YX7AVPtBZDG3l64zP7E/NuXOYCvm57r/7G3KIE4JU6i6Z3fYWYrbN0ON5k2EjUQ+Jt ZQgZxybuzmVXppKIeQ06qXzAZXIRGGbXnaHUVwQ/rxS/lygC1kmFcpAm3568aQzZQW+T ZSbKDZO9Oha2BJN4KwE9malHHY9RO7HfFLf9s2sQpwFa6Y1gJZYMkIBg6z6+pfZGAW6R bfhG8nLV5VF0eWqibjPANai8XmbyuiA0oKIZA6pHd5BLSa5Hgz6doZM15EOXCmaS4HWv iH2kR63GHdqtLCMfWN7Zu5azeWMTj7pao4OY453miTvTYzP6XlYn5Ee1RQQvuzoDzafR dk1Q== X-Gm-Message-State: APjAAAWaOy/hGJK2b8xZroEpCpBOgmFHyBIBRxF0qbGWSyxXeXB3ZDFi q9Dm5+aQn9ULmj9oBUx2lhFc5JQj X-Google-Smtp-Source: APXvYqzXibXZSd6IWrSK+XtEpTCaIi3keajeQLn0VdiXnOjUc33BTq98H530Us64OhTV+XaDB3T7Bw== X-Received: by 2002:a17:902:7791:: with SMTP id o17mr98018495pll.27.1564153736559; Fri, 26 Jul 2019 08:08:56 -0700 (PDT) Received: from joelaf.cam.corp.google.com ([2620:15c:6:12:9c46:e0da:efbf:69cc]) by smtp.gmail.com with ESMTPSA id k36sm54802352pgl.42.2019.07.26.08.08.53 (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Fri, 26 Jul 2019 08:08:55 -0700 (PDT) From: "Joel Fernandes (Google)" To: linux-kernel@vger.kernel.org Cc: "Joel Fernandes (Google)" , Alexey Dobriyan , Andrew Morton , Brendan Gregg , Christian Hansen , dancol@google.com, fmayer@google.com, joaodias@google.com, 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 , Mike Rapoport , minchan@kernel.org, namhyung@google.com, Roman Gushchin , Stephen Rothwell , surenb@google.com, tkjos@google.com, Vladimir Davydov , Vlastimil Babka , wvw@google.com Subject: [PATCH v2 2/2] doc: Update documentation for page_idle virtual address indexing Date: Fri, 26 Jul 2019 11:08:44 -0400 Message-Id: <20190726150845.95720-2-joel@joelfernandes.org> X-Mailer: git-send-email 2.22.0.709.g102302147b-goog In-Reply-To: <20190726150845.95720-1-joel@joelfernandes.org> References: <20190726150845.95720-1-joel@joelfernandes.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This patch updates the documentation with the new page_idle tracking feature which uses virtual address indexing. 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..1eeac78c94a7 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 page +frame numbers (VFN) 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 need deal with PFN so it does not require +prior lookups of ``pagemap`` in order to find if page is idle or not. 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 -- 2.22.0.709.g102302147b-goog