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 66AC1C54EE9 for ; Mon, 19 Sep 2022 14:58:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229699AbiISO6S (ORCPT ); Mon, 19 Sep 2022 10:58:18 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43600 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229473AbiISO6Q (ORCPT ); Mon, 19 Sep 2022 10:58:16 -0400 Received: from mail-pf1-x42a.google.com (mail-pf1-x42a.google.com [IPv6:2607:f8b0:4864:20::42a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6753A19C01; Mon, 19 Sep 2022 07:58:15 -0700 (PDT) Received: by mail-pf1-x42a.google.com with SMTP id w2so18085709pfb.0; 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=Qvr9UNS0APM/OpQtGCVuHQ+L6AQ4+JznjIPhSQX/PBTd6dlaLgBIpyu3hfrCAVPn5f WC/jVFLYJ8oy+jo9oCklcpYZCSdQGfNmLCQipsaPg5svwk7/QUP9LKFHvf+XXPeC/Vil QiW8x9PSleZHU4tAdXmUm7aEiudbqEiEW98BdhzoYzlUUOhN2xeSyj1SG3VOsxHy0La+ 44OGG7/H33gCLs76oowCTE7PkHfAj5OfpYkK8VSROrKxCHqTCapRXFcn+dOKVWvrJBoQ 8hOkHjfg5/BllwCHN8nGIopzHIVvpXhq82nB+c+3GDhLV5xjxGLH6C4M0e4jsM2YPGbp QPSQ== X-Gm-Message-State: ACrzQf3GHsgMe/BmfUr0bl8cW7Aw0HPK/dUzqNVG90kdJX0OlFdixW3s chqPxuygvu0Vm/yV9yUgfmw= 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> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 >