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[209.85.220.65]) by mx.google.com with SMTPS id bj2sor49424503plb.52.2019.07.22.14.32.22 for (Google Transport Security); Mon, 22 Jul 2019 14:32:22 -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=RN51VtIv; 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=Mv7+8jJEeDbo3rALIQWEE79IiSHFEfgtW30JPgsaJYY=; b=RN51VtIvabaQniuWGM+pEPP9sY4v3p6xCZKepJA4+4kregQ3NwAojuNej56xQ688W8 eLtSCHrEUHvqDuJG1YODwTmMS531wT5nr8f+7IPMA+tRi07n7hQ2+4nf6D7krbpHmVru +sIEA0pNjuayX8Cig3N0kz1/Ihvc6sa3pBBYo= X-Google-Smtp-Source: APXvYqzeYQTGy2llesIRc8Xr/1lEdoWOVbeDS/M3QnnnhYqXSV2haWsR6uhZcgSUQ/kYpp4/+92/Rw== X-Received: by 2002:a17:902:1566:: with SMTP id b35mr79260764plh.147.1563831141698; Mon, 22 Jul 2019 14:32:21 -0700 (PDT) Received: from joelaf.cam.corp.google.com ([2620:15c:6:12:9c46:e0da:efbf:69cc]) by smtp.gmail.com with ESMTPSA id i14sm65202333pfk.0.2019.07.22.14.32.17 (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Mon, 22 Jul 2019 14:32:20 -0700 (PDT) From: "Joel Fernandes (Google)" To: linux-kernel@vger.kernel.org Cc: "Joel Fernandes (Google)" , Alexey Dobriyan , Al Viro , Andrew Morton , Brendan Gregg , carmenjackson@google.com, Christian Hansen , Colin Ian King , dancol@google.com, David Howells , fmayer@google.com, joaodias@google.com, joelaf@google.com, Jonathan Corbet , Kees Cook , kernel-team@android.com, Kirill Tkhai , Konstantin Khlebnikov , linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, Michal Hocko , Mike Rapoport , minchan@google.com, minchan@kernel.org, namhyung@google.com, sspatil@google.com, surenb@google.com, Thomas Gleixner , timmurray@google.com, tkjos@google.com, vdavydov.dev@gmail.com, Vlastimil Babka , wvw@google.com Subject: [PATCH v1 2/2] doc: Update documentation for page_idle virtual address indexing Date: Mon, 22 Jul 2019 17:32:05 -0400 Message-Id: <20190722213205.140845-2-joel@joelfernandes.org> X-Mailer: git-send-email 2.22.0.657.g960e92d24f-goog In-Reply-To: <20190722213205.140845-1-joel@joelfernandes.org> References: <20190722213205.140845-1-joel@joelfernandes.org> MIME-Version: 1.0 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: 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 | 41 +++++++++++++++---- 1 file changed, 34 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..70d3bf6f1f8c 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 +78,29 @@ 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 can be simpler to use than physical address +indexing, since the ``pagemap`` for a process does not need to be looked up to +mark or read a page's idle bit. It is also more accurate than physical address +indexing since in physical address indexing, address space changes can occur +between reading the ``pagemap`` and reading the ``bitmap``. 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 +126,10 @@ 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