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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 95572C38145 for ; Wed, 7 Sep 2022 09:41:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229884AbiIGJlK (ORCPT ); Wed, 7 Sep 2022 05:41:10 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51464 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230206AbiIGJkr (ORCPT ); Wed, 7 Sep 2022 05:40:47 -0400 Received: from madras.collabora.co.uk (madras.collabora.co.uk [IPv6:2a00:1098:0:82:1000:25:2eeb:e5ab]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 878EE8C44A; Wed, 7 Sep 2022 02:40:46 -0700 (PDT) Received: from [192.168.10.7] (unknown [39.45.34.118]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 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 86B816601F59; Wed, 7 Sep 2022 10:40:41 +0100 (BST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1662543644; bh=uY9pFagbdbh2lu8qFd2KKrIN4d71jSAT6G/zm0gBKdA=; h=Date:Cc:Subject:To:References:From:In-Reply-To:From; b=bxbY5WxH4rDgMWoliFxR6YZ8Ia1K9Tiw4FBvay0lZQ/wFpp5fJPhe2OZ9kZJvKPtD U4zYvbBUaEPP654ir03KVcclG9hpZxVMhnXw1C0TCvJOoknbNfodO3HdVTP0rqsP5V cDqdEBqviA8BAhb9aFUJomTcw92gNg2Hc5Z7evMXLAy5F6uFtscHy7mlE0i2j+MW70 qylf+08rgESV6oVoor2i9EFePOJtK0Hp1zfCyKC9eC9AaQgKvtsCJyU/C0wtB4uOjG 2HAPUt63VEawgolQd37NugEEScwTS2kHaUR5gw5odZUkyiyENUQFi78Gr+la3TShER ytgxww5A5tn9A== Message-ID: <19df8db9-cff4-848e-905b-525f620848e8@collabora.com> Date: Wed, 7 Sep 2022 14:40:37 +0500 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.13.0 Cc: usama.anjum@collabora.com, kernel@collabora.com, Gabriel Krisman Bertazi , David Hildenbrand , Peter Enderborg , Greg KH Subject: Re: [PATCH v3 0/4] Implement IOCTL to get and clear soft dirty PTE Content-Language: en-US To: Jonathan Corbet , Alexander Viro , Andrew Morton , Shuah Khan , "open list:DOCUMENTATION" , open list , "open list:PROC FILESYSTEM" , "open list:MEMORY MANAGEMENT" , "open list:KERNEL SELFTEST FRAMEWORK" References: <20220826064535.1941190-1-usama.anjum@collabora.com> From: Muhammad Usama Anjum In-Reply-To: <20220826064535.1941190-1-usama.anjum@collabora.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 8/26/22 11:45 AM, Muhammad Usama Anjum wrote: > > Hello, > > This patch series implements a new ioctl on the pagemap proc fs file to > get, clear and perform both get and clear at the same time atomically on > the specified range of the memory. > > Soft-dirty PTE bit of the memory pages can be viewed by using pagemap > procfs file. The soft-dirty PTE bit for the whole memory range of the > process can be cleared by writing to the clear_refs file. This series > adds features that weren't present earlier. > - There is no atomic get soft-dirty PTE bit status and clear operation > present. > - The soft-dirty PTE bit of only a part of memory cannot be cleared. > > Historically, soft-dirty PTE bit tracking has been used in the CRIU > project. The proc fs interface is enough for that as I think the process > is frozen. We have the use case where we need to track the soft-dirty > PTE bit for the running processes. We need this tracking and clear > mechanism of a region of memory while the process is running to emulate > the getWriteWatch() syscall of Windows. This syscall is used by games to > keep track of dirty pages and keep processing only the dirty pages. This > new ioctl can be used by the CRIU project and other applications which > require soft-dirty PTE bit information. > > As in the current kernel there is no way to clear a part of memory (instead > of clearing the Soft-Dirty bits for the entire process) and get+clear > operation cannot be performed atomically, there are other methods to mimic > this information entirely in userspace with poor performance: > - The mprotect syscall and SIGSEGV handler for bookkeeping > - The userfaultfd syscall with the handler for bookkeeping > Some benchmarks can be seen [1]. > > This ioctl can be used by the CRIU project and other applications which > require soft-dirty PTE bit information. The following operations are > supported in this ioctl: > - Get the pages that are soft-dirty. > - Clear the pages which are soft-dirty. > - The optional flag to ignore the VM_SOFTDIRTY and only track per page > soft-dirty PTE bit Thoughts? > > There are two decisions which have been taken about how to get the output > from the syscall. > - Return offsets of the pages from the start in the vec > - Stop execution when vec is filled with dirty pages > These two arguments doesn't follow the mincore() philosophy where the > output array corresponds to the address range in one to one fashion, hence > the output buffer length isn't passed and only a flag is set if the page > is present. This makes mincore() easy to use with less control. We are > passing the size of the output array and putting return data consecutively > which is offset of dirty pages from the start. The user can convert these > offsets back into the dirty page addresses easily. Suppose, the user want > to get first 10 dirty pages from a total memory of 100 pages. He'll > allocate output buffer of size 10 and the ioctl will abort after finding the > 10 pages. This behaviour is needed to support Windows' getWriteWatch(). The > behaviour like mincore() can be achieved by passing output buffer of 100 > size. This interface can be used for any desired behaviour. > > [1] https://lore.kernel.org/lkml/54d4c322-cd6e-eefd-b161-2af2b56aae24@collabora.com/ > > Regards, > Muhammad Usama Anjum > > Muhammad Usama Anjum (4): > fs/proc/task_mmu: update functions to clear the soft-dirty PTE bit > fs/proc/task_mmu: Implement IOCTL to get and clear soft dirty PTE bit > selftests: vm: add pagemap ioctl tests > mm: add documentation of the new ioctl on pagemap > > Documentation/admin-guide/mm/soft-dirty.rst | 42 +- > fs/proc/task_mmu.c | 342 ++++++++++- > include/uapi/linux/fs.h | 23 + > tools/include/uapi/linux/fs.h | 23 + > tools/testing/selftests/vm/.gitignore | 1 + > tools/testing/selftests/vm/Makefile | 2 + > tools/testing/selftests/vm/pagemap_ioctl.c | 649 ++++++++++++++++++++ > 7 files changed, 1050 insertions(+), 32 deletions(-) > create mode 100644 tools/testing/selftests/vm/pagemap_ioctl.c > -- Muhammad Usama Anjum