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 E9F49C6FA82 for ; Wed, 21 Sep 2022 18:30:29 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 446ED940008; Wed, 21 Sep 2022 14:30:29 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 3F73C940007; Wed, 21 Sep 2022 14:30:29 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 2974A940008; Wed, 21 Sep 2022 14:30:29 -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 1B8EB940007 for ; Wed, 21 Sep 2022 14:30:29 -0400 (EDT) Received: from smtpin11.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay05.hostedemail.com (Postfix) with ESMTP id E60A8405CC for ; Wed, 21 Sep 2022 18:30:28 +0000 (UTC) X-FDA: 79936932936.11.AFD9ACB Received: from madras.collabora.co.uk (madras.collabora.co.uk [46.235.227.172]) by imf24.hostedemail.com (Postfix) with ESMTP id 6636E180008 for ; Wed, 21 Sep 2022 18:30:28 +0000 (UTC) Received: from [192.168.10.9] (unknown [39.45.34.16]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits)) (No client certificate requested) (Authenticated sender: usama.anjum) by madras.collabora.co.uk (Postfix) with ESMTPSA id 35B1A6601F3F; Wed, 21 Sep 2022 19:30:24 +0100 (BST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1663785027; bh=BbYZK5kjusKrIzNZUnjNshwXR92l04FpzHFY3oAXOF8=; h=Date:Cc:Subject:To:References:From:In-Reply-To:From; b=dN+DilH/wnaFUJha/f9OBaTCtJ6DFgoJK3l36TGxNBiPRssCKNcwUvcyf8XaPbbs5 p+wQQtinjAwPUk6viinSpyeBt5zSg8MqKoVBdthJ4refOtSR8TxHtulRa+Jbg4lYeO Kbfpu1w+Xxe5FUMw49jmvbcFcPEBBvmJdBit9KgzmL6sShDfUnZCXogJtrsvtbeTQv fgi3I7i+K+gzwQ+XB2CzmkQxg9PwfRFOhbkzXTKaVIgFx5xSona7MR0t0BuqeWBABD PO1UZm+rxhGvfmrXLyGBl55mZz2Aq65gw72hB2BKMK4wLH18y+XKu+gias70wj/rQM JJRS6GALkD1Pw== Message-ID: Date: Wed, 21 Sep 2022 23:30:21 +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 , 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" Subject: Re: [PATCH v3 0/4] Implement IOCTL to get and clear soft dirty PTE Content-Language: en-US To: Suren Baghdasaryan 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 ARC-Authentication-Results: i=1; imf24.hostedemail.com; dkim=pass header.d=collabora.com header.s=mail header.b="dN+DilH/"; dmarc=pass (policy=none) header.from=collabora.com; spf=pass (imf24.hostedemail.com: domain of usama.anjum@collabora.com designates 46.235.227.172 as permitted sender) smtp.mailfrom=usama.anjum@collabora.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1663785028; a=rsa-sha256; cv=none; b=ks9V2Ch60l+pGCUcDm4TT/stdfx8cNzogITV4h6CLE0yrGVO285noTLm0sCzv5tBMD+5lf 8pMSvNbrn6jwIRZFs7RJncM+LJfKEB77CYaoc78MZCwoKvu6QDMCc5CF4ZCe2Z8gfJod1X JgWoMzO2nFHpQV7xCY0L6wKPGt0lWp4= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1663785028; 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:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=0rSQrtXTth4dXH/7Dtlmj6pEMXHPYYmXL0k7qILgSDw=; b=rhy5G3Ot8CvncApgo5jZ+torgPCOcpfGGVBeNQ3SbUTKq3SchWJOobYyNpD/Yn4IMfevDr DxPKMKJN2cTUyrw7ETiwremXCnazcm1z7xxPb2ouM2fzJOVaob+1SEL9gvpzj5e1h/hix9 H/l6gghef5G3Ee6fKWVGoZeuzD6joI0= Authentication-Results: imf24.hostedemail.com; dkim=pass header.d=collabora.com header.s=mail header.b="dN+DilH/"; dmarc=pass (policy=none) header.from=collabora.com; spf=pass (imf24.hostedemail.com: domain of usama.anjum@collabora.com designates 46.235.227.172 as permitted sender) smtp.mailfrom=usama.anjum@collabora.com X-Rspamd-Server: rspam06 X-Stat-Signature: jrptmtxy84f7pa6ios6z9fj1qpbuwxxy X-Rspam-User: X-Rspamd-Queue-Id: 6636E180008 X-HE-Tag: 1663785028-662800 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: Hi Suren, I'd shared this problem with you at Plumbers. Please review and share your thoughts. Thanks, Usama 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 > > 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