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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 52424C54EE9 for ; Mon, 19 Sep 2022 14:58:17 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id BAD4E6B0072; Mon, 19 Sep 2022 10:58:16 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id B5C4C80007; Mon, 19 Sep 2022 10:58:16 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 9D5C06B0074; Mon, 19 Sep 2022 10:58:16 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0013.hostedemail.com [216.40.44.13]) by kanga.kvack.org (Postfix) with ESMTP id 896DF6B0072 for ; Mon, 19 Sep 2022 10:58:16 -0400 (EDT) Received: from smtpin18.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay02.hostedemail.com (Postfix) with ESMTP id 5171B121CB7 for ; Mon, 19 Sep 2022 14:58:16 +0000 (UTC) X-FDA: 79929140592.18.FE4CF81 Received: from mail-pf1-f174.google.com (mail-pf1-f174.google.com [209.85.210.174]) by imf26.hostedemail.com (Postfix) with ESMTP id 0014414000A for ; Mon, 19 Sep 2022 14:58:15 +0000 (UTC) Received: by mail-pf1-f174.google.com with SMTP id a29so4738852pfk.5 for ; Mon, 19 Sep 2022 07:58:15 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date; bh=lnYJozcLUmTPYrU24R8V0lK2TwtYqvaT/IHSXf9uJg0=; b=hRmZP+oV1Bl8EjCD8HfT0GqgLngvsP/aBaoWTJ1ML06z73Xew4hyq/urnklLSYH3/q dMPY4mFzOip3Hsohb93b7CLrlknDnOe/YktWjjXLDjm6POoYbFn/tds3R2oy1BleZjSd ThdYET2VaFoimTq2WMbSzrMwONsyEuf+BbWVFjYn+yHXDGIr5BnnT3vcx7Gh0F0WzY/p UyPnLDLeZ+3OLuFYxtytUFI9A9D+YQsIRvdjN4Vbw3aWKFqXeYacSAt2wzSCLCm6BCA1 Mo9MaxLow+r5p7N7q9QGNHdmyFNlnoiBVMgP+AFPXrq2mqMyaPABJXUP2NQ8TuNOElrQ s6ug== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date; bh=lnYJozcLUmTPYrU24R8V0lK2TwtYqvaT/IHSXf9uJg0=; b=V0qJNYw8huMKUeln9rldTW0Zv01jrHxB4wnSwPjIizlAT7mwCbeSg5oJPIgLTaiQKv 98tzaEWnXUh3ozCF9HlYspms9gsoW8M1Yj9WP0ASTlQ6/BqO8Rq8l2Mr10JfjZJHT6Rh 7vP8yThGd9CXdrhIIan1TwTmfqZiZh1lLkBo4Fo8zuAY7Qcx2P6aGwsemvdCykzFjtaY MxHcN7/NcOJDoJeAx8mmZUh7xfM1Ym2qqQ93oASibmf/hHGAicUd6S6/+yGyjEGmRacl 6SjS+AR8xi7W8wv+VPKhVb35BG8sM+zeGFvmj88FiAAdVbAQw4dGMSg03nP35xzW85Xc QlUQ== X-Gm-Message-State: ACrzQf10xkXFBDFWxPRi0ErzOhMY5qQfr7GQN/7337bKV4F1zOBo3K8Y Ar+fnRuswUVYRoatakyZ4zM= X-Google-Smtp-Source: AMsMyM5ZYYdFuNeKzgLJKAadbdkw3BGTjlQj6CuVcT73oxkvecA7RXzVRlY7rFhCUdnWPJ2uEHW6bw== X-Received: by 2002:a05:6a00:3392:b0:547:f861:1fad with SMTP id cm18-20020a056a00339200b00547f8611fadmr19226573pfb.16.1663599494511; Mon, 19 Sep 2022 07:58:14 -0700 (PDT) Received: from gmail.com ([2601:600:8500:5f14:d627:c51e:516e:a105]) by smtp.gmail.com with ESMTPSA id p14-20020a170902e74e00b00177324a7862sm21108171plf.45.2022.09.19.07.58.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 19 Sep 2022 07:58:13 -0700 (PDT) Date: Mon, 19 Sep 2022 07:58:11 -0700 From: Andrei Vagin To: Muhammad Usama Anjum Cc: 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" , 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 Message-ID: References: <20220826064535.1941190-1-usama.anjum@collabora.com> MIME-Version: 1.0 Content-Type: text/plain; charset=koi8-r Content-Disposition: inline In-Reply-To: <20220826064535.1941190-1-usama.anjum@collabora.com> ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1663599496; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=lnYJozcLUmTPYrU24R8V0lK2TwtYqvaT/IHSXf9uJg0=; b=YqkLs7rpto6YW+76trGUikA+T/hdNsiGryGHW0WJYVBrDYVeddNm6NOEGaOPMAyBLU+qCz WvfdyPkr8q+xZOMmsL6a5OlI9gbg1VqYIyYq9r4FSslsj3qizTGv0ZfDMWCMzyvBjNS873 yHxl+RzRl/P2+G+ez8hMB8vqvrt4eKI= ARC-Authentication-Results: i=1; imf26.hostedemail.com; dkim=pass header.d=gmail.com header.s=20210112 header.b=hRmZP+oV; spf=pass (imf26.hostedemail.com: domain of avagin@gmail.com designates 209.85.210.174 as permitted sender) smtp.mailfrom=avagin@gmail.com; dmarc=pass (policy=none) header.from=gmail.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1663599496; a=rsa-sha256; cv=none; b=qoNGsFTfgL7puD9BzI5o5sXkq3t1KFCxQCryTUNgHAAG9j0e5473pLqZ8JV6K+vyfl5A6h IYhOGp4/Kncp9fnDsRlhPI1XMo+cnXu4HDhEJ8uAwlRjDaR7PHy/8hD1hiXlqXKYvC8ttZ 4lB3yR1JLWY4AqMTUXk7i+cEZiI92YQ= X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 0014414000A X-Rspam-User: Authentication-Results: imf26.hostedemail.com; dkim=pass header.d=gmail.com header.s=20210112 header.b=hRmZP+oV; spf=pass (imf26.hostedemail.com: domain of avagin@gmail.com designates 209.85.210.174 as permitted sender) smtp.mailfrom=avagin@gmail.com; dmarc=pass (policy=none) header.from=gmail.com X-Stat-Signature: wc9c7dt5xtbo8tg98t514u18d6djetfz X-HE-Tag: 1663599495-582189 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: On Fri, Aug 26, 2022 at 11:45:31AM +0500, 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. I think this interface doesn't have to be limited by the soft-dirty bits only. For example, CRIU needs to know whether file, present and swap bits are set or not. I mean we should be able to specify for what pages we need to get info for. An ioctl argument can have these four fields: * required bits (rmask & mask == mask) - all bits from this mask have to be set. * any of these bits (amask & mask != 0) - any of these bits is set. * exclude masks (emask & mask == 0) = none of these bits are set. * return mask - bits that have to be reported to user. > - Clear the pages which are soft-dirty. > - The optional flag to ignore the VM_SOFTDIRTY and only track per page > soft-dirty PTE bit > > 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 We can conside to return regions that contains pages with the same set of bits. struct page_region { void *start; long size; u64 bitmap; } And ioctl returns arrays of page_region-s. I believe it will be more compact form for many cases. > - 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 > > -- > 2.30.2 >