From patchwork Fri Jul 26 15:08:44 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Joel Fernandes X-Patchwork-Id: 11061223 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id E74C713A0 for ; Fri, 26 Jul 2019 15:09:11 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id D685428B3E for ; Fri, 26 Jul 2019 15:09:11 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id CA43D28B45; Fri, 26 Jul 2019 15:09:11 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.0 required=2.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI autolearn=unavailable version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 601C328B37 for ; Fri, 26 Jul 2019 15:09:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728375AbfGZPI6 (ORCPT ); Fri, 26 Jul 2019 11:08:58 -0400 Received: from mail-pl1-f193.google.com ([209.85.214.193]:43544 "EHLO mail-pl1-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727679AbfGZPI5 (ORCPT ); Fri, 26 Jul 2019 11:08:57 -0400 Received: by mail-pl1-f193.google.com with SMTP id 4so17887678pld.10 for ; Fri, 26 Jul 2019 08:08:56 -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=RU8p9tZTPmymESCqKkKTizMPccIuAR/2y+XwhtTIGrtSzfFWfL9cLm+19WDpJyxhWL dV+/sT+sD/1eE0NDA0VEZdrpsSuYVu+6dEzK+Jhn0DMDduOBr5nhllrav3xbvXIhlZAo SpObozoDjZLpx+btj93SWyxxndIX/lL0WCCfsnh3/4sp+1AK561WHj2n2hyXqU5aottc 8DBTzTvOOt+wWwJcJdjazNDaHMBJZUCueMD6ntsTOnAeKFURJM0BCw2aEttxLR1QpZ+W XgOoT0zAapYvdGvab3bhvwuFImRfEoQLOrNk9rVp9u/e+DtjPRrYm+hcLupUpHJfbE8/ WShA== X-Gm-Message-State: APjAAAXsJ76hdlV0EDXWRrimzXr+aZnXR7l3J98hc4n9D5vHQLwUvVH8 2hMSRz8t1w4XZt77yullbRc= 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 Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP 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