From patchwork Thu Aug 25 07:09:26 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Muhammad Usama Anjum X-Patchwork-Id: 12954263 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0C06AC28D13 for ; Thu, 25 Aug 2022 07:10:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237347AbiHYHKL (ORCPT ); Thu, 25 Aug 2022 03:10:11 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44420 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237197AbiHYHKF (ORCPT ); Thu, 25 Aug 2022 03:10:05 -0400 Received: from madras.collabora.co.uk (madras.collabora.co.uk [46.235.227.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8CF4C31379; Thu, 25 Aug 2022 00:10:02 -0700 (PDT) Received: from lenovo.Home (unknown [39.53.61.43]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) (Authenticated sender: usama.anjum) by madras.collabora.co.uk (Postfix) with ESMTPSA id E66546601E9C; Thu, 25 Aug 2022 08:09:58 +0100 (BST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1661411401; bh=qFwfAW+YdGQMEoUt1Jsqu4meeyL+SBRRa4jSpOBxxag=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Bx/9rVPU+JTiTRGq6yKLfsVSVb5l7v9f/qPpy7CBWa0cJUDj+xYFFMRaY1jmAeFth nuqIe9jNrr3lohnEK9M67it9OomP2JbkAK3gTNI4/s8h/d1MGjm54kIIKSI682fQNy oSDyudVxA60s1YOELUYREVVfC033R1ILywyNy7kWoJG5YzPobioz9IYw6SJ0IXuOfR EKByu1vasxgHu5DwxLGW1nnNS2Aq4WIjnkwuBi0HN3BSqIdsMDZ5YXi51yyES4bzGM cO++TskZMNgLzfDHY9BIz/vrEtu/h+VRL6qGJt4tgZpPCrafRy6THV4q/2NMCekJDc D7i43/jy/FPJw== From: Muhammad Usama Anjum To: Jonathan Corbet , Alexander Viro , Andrew Morton , Shuah Khan , linux-doc@vger.kernel.org (open list:DOCUMENTATION), linux-kernel@vger.kernel.org (open list), linux-fsdevel@vger.kernel.org (open list:PROC FILESYSTEM), linux-mm@kvack.org (open list:MEMORY MANAGEMENT), linux-kselftest@vger.kernel.org (open list:KERNEL SELFTEST FRAMEWORK) Cc: Muhammad Usama Anjum , kernel@collabora.com Subject: [PATCH v2 4/4] mm: add documentation of the new ioctl on pagemap Date: Thu, 25 Aug 2022 12:09:26 +0500 Message-Id: <20220825070926.2922471-5-usama.anjum@collabora.com> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20220825070926.2922471-1-usama.anjum@collabora.com> References: <20220825070926.2922471-1-usama.anjum@collabora.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org Add the explanation of the added ioctl on pagemap file. It can be used to get, clear or both soft-dirty PTE bit of the specified range. or both at the same time. Signed-off-by: Muhammad Usama Anjum --- Changes in v2: - Update documentation to mention ioctl instead of the syscall --- Documentation/admin-guide/mm/soft-dirty.rst | 42 ++++++++++++++++++++- 1 file changed, 41 insertions(+), 1 deletion(-) diff --git a/Documentation/admin-guide/mm/soft-dirty.rst b/Documentation/admin-guide/mm/soft-dirty.rst index cb0cfd6672fa..d3d33e63a965 100644 --- a/Documentation/admin-guide/mm/soft-dirty.rst +++ b/Documentation/admin-guide/mm/soft-dirty.rst @@ -5,7 +5,12 @@ Soft-Dirty PTEs =============== The soft-dirty is a bit on a PTE which helps to track which pages a task -writes to. In order to do this tracking one should +writes to. + +Using Proc FS +------------- + +In order to do this tracking one should 1. Clear soft-dirty bits from the task's PTEs. @@ -20,6 +25,41 @@ writes to. In order to do this tracking one should 64-bit qword is the soft-dirty one. If set, the respective PTE was written to since step 1. +Using IOCTL +----------- + +The IOCTL on the ``/proc/PID/pagemap`` can be can be used to find the dirty pages +atomically. The following commands are supported:: + + MEMWATCH_SD_GET + Get the page offsets which are soft dirty. + + MEMWATCH_SD_CLEAR + Clear the pages which are soft dirty. + + MEMWATCH_SD_GET_AND_CLEAR + Get and clear the pages which are soft dirty. + +The struct :c:type:`pagemap_sd_args` is used as the argument. In this struct: + + 1. The range is specified through start and len. The len argument need not be + the multiple of the page size, but since the information is returned for the + whole pages, len is effectively rounded up to the next multiple of the page + size. + + 2. The output buffer and size is specified in vec and vec_len. The offsets of + the dirty pages from start are returned in vec. The ioctl returns when the + whole range has been searched or vec is completely filled. The whole range + isn't cleared if vec fills up completely. + + 3. The flags can be specified in flags field. Currently only one flag, + PAGEMAP_SD_NO_REUSED_REGIONS is supported which can be specified to ignore + the VMA dirty flags for better performance. This flag shows only those pages + dirty which have been written to by the user. All new allocations aren't returned + to be dirty. + +Explanation +----------- Internally, to do this tracking, the writable bit is cleared from PTEs when the soft-dirty bit is cleared. So, after this, when the task tries to