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[209.85.220.65]) by mx.google.com with SMTPS id f41sor793385pjg.15.2019.08.07.10.16.28 for (Google Transport Security); Wed, 07 Aug 2019 10:16:28 -0700 (PDT) Received-SPF: pass (google.com: domain of joel@joelfernandes.org designates 209.85.220.65 as permitted sender) client-ip=209.85.220.65; Authentication-Results: mx.google.com; dkim=pass header.i=@joelfernandes.org header.s=google header.b=qSJJinjx; spf=pass (google.com: domain of joel@joelfernandes.org designates 209.85.220.65 as permitted sender) smtp.mailfrom=joel@joelfernandes.org 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=qSJJinjx4WgXKOGFZMmrrGe4d2ALaNficzckUCKQ9VzSczmwMe7F1Cq0uQ7tfoks+e rtGpQwgXk30A1hVz+miPyOItSF28qM821PY2ovorbdNSmTsSYUUDhgdU2OE+wjQDzDPX CSpRQfnNtyIHoIY+g92oO+tp+BGpBJMqcqBT0= X-Google-Smtp-Source: APXvYqwFZ4pqna4e9p6C0a1Fkqp6qRc76QmaknFJcHpGMEiflBOSwsFgniRNvWcMNGSw3sFAcWvCGQ== X-Received: by 2002:a17:90a:7148:: with SMTP id g8mr938080pjs.51.1565198187764; Wed, 07 Aug 2019 10:16:27 -0700 (PDT) Received: from joelaf.cam.corp.google.com ([2620:15c:6:12:9c46:e0da:efbf:69cc]) by smtp.gmail.com with ESMTPSA id a1sm62692130pgh.61.2019.08.07.10.16.23 (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Wed, 07 Aug 2019 10:16:26 -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 v5 6/6] doc: Update documentation for page_idle virtual address indexing Date: Wed, 7 Aug 2019 13:15:59 -0400 Message-Id: <20190807171559.182301-6-joel@joelfernandes.org> X-Mailer: git-send-email 2.22.0.770.g0f2c4a37fd-goog In-Reply-To: <20190807171559.182301-1-joel@joelfernandes.org> References: <20190807171559.182301-1-joel@joelfernandes.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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: 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