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 X-Spam-Level: X-Spam-Status: No, score=-3.9 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C00D2C433E7 for ; Fri, 9 Oct 2020 11:54:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 582C02226B for ; Fri, 9 Oct 2020 11:54:42 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=oracle.com header.i=@oracle.com header.b="Jtl7dgY4" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388243AbgJILyl (ORCPT ); Fri, 9 Oct 2020 07:54:41 -0400 Received: from aserp2130.oracle.com ([141.146.126.79]:52848 "EHLO aserp2130.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732480AbgJILyk (ORCPT ); Fri, 9 Oct 2020 07:54:40 -0400 Received: from pps.filterd (aserp2130.oracle.com [127.0.0.1]) by aserp2130.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 099BocOe079912; Fri, 9 Oct 2020 11:53:20 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=subject : to : cc : references : from : message-id : date : mime-version : in-reply-to : content-type : content-transfer-encoding; s=corp-2020-01-29; bh=gC3p3SG+FOYjnql41FZPAxse6J88pzuXf0fi/UYfcFE=; b=Jtl7dgY4XPEm8DTdUcFPeLJSJEnIG9CUlxdDNhmpftpZj+ZN53wq3Uo9m7YGhAJcrMkg osRBeTCrsz+5makM+wcSscIeTidVW7vArJpjt26bmxz/zMY79SbytBAwrEjMZrcujcEE uqdgLKGqoN/1GpJkTFvtgBnPjB5x4C9FvGnwLx73G//xhkjMksMblxagD6ff9EZj8EUK QtNKQiljaQ6sJbp/qCTXiAl3t9uA+KMQJHlSPOE5cLURt1b+tFPwMj+YDL0r0xb5uK2Y NP4y42FMJ+G2v9/qHkVP/C5+vACRsti46QbUOK/itZss723T8mjoV6akW/5Tu2V6jMM4 cQ== Received: from aserp3030.oracle.com (aserp3030.oracle.com [141.146.126.71]) by aserp2130.oracle.com with ESMTP id 342kvys2hm-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL); Fri, 09 Oct 2020 11:53:20 +0000 Received: from pps.filterd (aserp3030.oracle.com [127.0.0.1]) by aserp3030.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 099BpP3I156582; Fri, 9 Oct 2020 11:53:20 GMT Received: from userv0122.oracle.com (userv0122.oracle.com [156.151.31.75]) by aserp3030.oracle.com with ESMTP id 342gurbwfq-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Fri, 09 Oct 2020 11:53:20 +0000 Received: from abhmp0015.oracle.com (abhmp0015.oracle.com [141.146.116.21]) by userv0122.oracle.com (8.14.4/8.14.4) with ESMTP id 099BrEPL001428; Fri, 9 Oct 2020 11:53:14 GMT Received: from [10.175.178.74] (/10.175.178.74) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Fri, 09 Oct 2020 04:53:14 -0700 Subject: Re: [PATCH 00/35] Enhance memory utilization with DMEMFS To: yulei zhang Cc: linux-fsdevel@vger.kernel.org, kvm , LKML , Xiao Guangrong , Wanpeng Li , Haiwei Li , Yulei Zhang , akpm@linux-foundation.org, naoya.horiguchi@nec.com, viro@zeniv.linux.org.uk, Paolo Bonzini , Matthew Wilcox , Mike Kravetz , Jane Y Chu , Dan Williams , Muchun Song , Konrad Rzeszutek Wilk References: From: Joao Martins Message-ID: Date: Fri, 9 Oct 2020 12:53:08 +0100 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9768 signatures=668681 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 mlxlogscore=999 phishscore=0 bulkscore=0 malwarescore=0 mlxscore=0 spamscore=0 adultscore=0 suspectscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2010090084 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9768 signatures=668681 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 malwarescore=0 clxscore=1015 phishscore=0 spamscore=0 mlxlogscore=999 impostorscore=0 priorityscore=1501 suspectscore=0 bulkscore=0 adultscore=0 lowpriorityscore=0 mlxscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2010090084 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/9/20 12:39 PM, yulei zhang wrote: > Joao, thanks a lot for the feedback. One more thing needs to mention > is that dmemfs also support fine-grained > memory management which makes it more flexible for tenants with > different requirements. > So as DAX when it allows to partition a region (starting 5.10). Meaning you have a region which you dedicated to userspace. That region can then be partitioning into devices which give you access to multiple (possibly discontinuous) extents with at a given page granularity (selectable when you create the device), accessed through mmap(). You can then give that device to a cgroup. Or you can return that memory back to the kernel (should you run into OOM situation), or you recreate the same mappings across reboot/kexec. I probably need to read your patches again, but can you extend on the 'dmemfs also support fine-grained memory management' to understand what is the gap that you mention? > On Fri, Oct 9, 2020 at 3:01 AM Joao Martins wrote: >> >> [adding a couple folks that directly or indirectly work on the subject] >> >> On 10/8/20 8:53 AM, yulei.kernel@gmail.com wrote: >>> From: Yulei Zhang >>> >>> In current system each physical memory page is assocaited with >>> a page structure which is used to track the usage of this page. >>> But due to the memory usage rapidly growing in cloud environment, >>> we find the resource consuming for page structure storage becomes >>> highly remarkable. So is it an expense that we could spare? >>> >> Happy to see another person working to solve the same problem! >> >> I am really glad to see more folks being interested in solving >> this problem and I hope we can join efforts? >> >> BTW, there is also a second benefit in removing struct page - >> which is carving out memory from the direct map. >> >>> This patchset introduces an idea about how to save the extra >>> memory through a new virtual filesystem -- dmemfs. >>> >>> Dmemfs (Direct Memory filesystem) is device memory or reserved >>> memory based filesystem. This kind of memory is special as it >>> is not managed by kernel and most important it is without 'struct page'. >>> Therefore we can leverage the extra memory from the host system >>> to support more tenants in our cloud service. >>> >> This is like a walk down the memory lane. >> >> About a year ago we followed the same exact idea/motivation to >> have memory outside of the direct map (and removing struct page overhead) >> and started with our own layer/thingie. However we realized that DAX >> is one the subsystems which already gives you direct access to memory >> for free (and is already upstream), plus a couple of things which we >> found more handy. >> >> So we sent an RFC a couple months ago: >> >> https://lore.kernel.org/linux-mm/20200110190313.17144-1-joao.m.martins@oracle.com/ >> >> Since then majority of the work has been in improving DAX[1]. >> But now that is done I am going to follow up with the above patchset. >> >> [1] >> https://lore.kernel.org/linux-mm/159625229779.3040297.11363509688097221416.stgit@dwillia2-desk3.amr.corp.intel.com/ >> >> (Give me a couple of days and I will send you the link to the latest >> patches on a git-tree - would love feedback!) >> >> The struct page removal for DAX would then be small, and ticks the >> same bells and whistles (MCE handling, reserving PAT memtypes, ptrace >> support) that we both do, with a smaller diffstat and it doesn't >> touch KVM (not at least fundamentally). >> >> 15 files changed, 401 insertions(+), 38 deletions(-) >> >> The things needed in core-mm is for handling PMD/PUD PAGE_SPECIAL much >> like we both do. Furthermore there wouldn't be a need for a new vm type, >> consuming an extra page bit (in addition to PAGE_SPECIAL) or new filesystem. >> >> [1] >> https://lore.kernel.org/linux-mm/159625229779.3040297.11363509688097221416.stgit@dwillia2-desk3.amr.corp.intel.com/ >> >> >>> We uses a kernel boot parameter 'dmem=' to reserve the system >>> memory when the host system boots up, the details can be checked >>> in /Documentation/admin-guide/kernel-parameters.txt. >>> >>> Theoretically for each 4k physical page it can save 64 bytes if >>> we drop the 'struct page', so for guest memory with 320G it can >>> save about 5G physical memory totally. >>> >> Also worth mentioning that if you only care about 'struct page' cost, and not on the >> security boundary, there's also some work on hugetlbfs preallocation of hugepages into >> tricking vmemmap in reusing tail pages. >> >> https://lore.kernel.org/linux-mm/20200915125947.26204-1-songmuchun@bytedance.com/ >> >> Going forward that could also make sense for device-dax to avoid so many >> struct pages allocated (which would require its transition to compound >> struct pages like hugetlbfs which we are looking at too). In addition an >> idea would be perhaps to have a stricter mode in DAX where >> we initialize/use the metadata ('struct page') but remove the underlaying >> PFNs (of the 'struct page') from the direct map having to bear the cost of >> mapping/unmapping on gup/pup. >> >> Joao