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=-2.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 6F47FC432C0 for ; Tue, 26 Nov 2019 00:05:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3F850207FD for ; Tue, 26 Nov 2019 00:05:17 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=oracle.com header.i=@oracle.com header.b="m5xHGr4g" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726926AbfKZAFQ (ORCPT ); Mon, 25 Nov 2019 19:05:16 -0500 Received: from userp2120.oracle.com ([156.151.31.85]:53030 "EHLO userp2120.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726118AbfKZAFQ (ORCPT ); Mon, 25 Nov 2019 19:05:16 -0500 Received: from pps.filterd (userp2120.oracle.com [127.0.0.1]) by userp2120.oracle.com (8.16.0.27/8.16.0.27) with SMTP id xAQ04t2S098452; Tue, 26 Nov 2019 00:05:09 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-2019-08-05; bh=mHXanxHdP89INCbUw8YABR16c/whANpUfRsLAPuh01A=; b=m5xHGr4g40ZJdiTPttDJBElLhud2J2DhoU1Ixt/I8KETzr0Dy3UBnO+yFzOygDoXtuRy YPxAiCoG3nGJfj8q7P+njVUsI42z/iHXthO8REKiLUtS7Ly0aScuvnzGeBvlZBQ+AKjV IhoX/l/j9XJiJUIb9/awfG5kN8RkT2JJERpBup8RR7qIAL32Da+M6la7Lw4bRY4JrBOr iYWVXWBOqZGQMsLqPSIS0vz91cUNLV0pYBEVjeLiCV/e/4h/ei+3Eho4cOtl+YVnpcZW 7W/opzCZQgmgt+f1qjYa4f8oW/tPZFoV4KGuw/Bpm/OQnzJrBp8IT5tEEh4vrrSb/TCe lA== Received: from userp3020.oracle.com (userp3020.oracle.com [156.151.31.79]) by userp2120.oracle.com with ESMTP id 2wewdr2vus-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 26 Nov 2019 00:05:09 +0000 Received: from pps.filterd (userp3020.oracle.com [127.0.0.1]) by userp3020.oracle.com (8.16.0.27/8.16.0.27) with SMTP id xAQ03Vuf020608; Tue, 26 Nov 2019 00:05:09 GMT Received: from aserv0121.oracle.com (aserv0121.oracle.com [141.146.126.235]) by userp3020.oracle.com with ESMTP id 2wfewbbd8q-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 26 Nov 2019 00:05:08 +0000 Received: from abhmp0014.oracle.com (abhmp0014.oracle.com [141.146.116.20]) by aserv0121.oracle.com (8.14.4/8.13.8) with ESMTP id xAQ057Dq005014; Tue, 26 Nov 2019 00:05:07 GMT Received: from [192.168.1.206] (/71.63.128.209) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Mon, 25 Nov 2019 16:05:07 -0800 Subject: Re: [PATCH v8 2/9] hugetlb_cgroup: add interface for charge/uncharge hugetlb reservations To: Mina Almasry , Shakeel Butt , David Rientjes Cc: shuah , open list , linux-mm@kvack.org, linux-kselftest@vger.kernel.org, cgroups@vger.kernel.org, Aneesh Kumar References: <20191030013701.39647-1-almasrymina@google.com> <20191030013701.39647-2-almasrymina@google.com> <9e10c273-f0ab-4173-570e-26c314b989fb@oracle.com> <3f30658c-0e3d-7d5c-4de9-1526b9bac3ce@oracle.com> From: Mike Kravetz Message-ID: <3b65b0ac-54ed-6e0d-706c-358d85057403@oracle.com> Date: Mon, 25 Nov 2019 16:05:06 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.2 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=9452 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1911140001 definitions=main-1911250187 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9452 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1911140001 definitions=main-1911250187 Sender: linux-kselftest-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org On 11/25/19 12:26 PM, Mina Almasry wrote: > On Fri, Nov 8, 2019 at 4:46 PM Mike Kravetz wrote: >> >> On 11/8/19 4:40 PM, Mina Almasry wrote: >>> On Fri, Nov 8, 2019 at 4:01 PM Mike Kravetz wrote: >>>> >>>> On 11/8/19 3:48 PM, Mina Almasry wrote: >>>>> On Thu, Nov 7, 2019 at 4:57 PM Mike Kravetz wrote: >>>>>> >>>>>> On 10/29/19 6:36 PM, Mina Almasry wrote: >>>>>>> >>>>>>> +static void hugetlb_cgroup_move_parent_reservation(int idx, >>>>>>> + struct hugetlb_cgroup *h_cg) >>>>>>> +{ >>>>>>> + struct hugetlb_cgroup *parent = parent_hugetlb_cgroup(h_cg); >>>>>>> + >>>>>>> + /* Move the reservation counters. */ >>>>>>> + if (!parent_hugetlb_cgroup(h_cg)) { >>>>>>> + parent = root_h_cgroup; >>>>>>> + /* root has no limit */ >>>>>>> + page_counter_charge( >>>>>>> + &root_h_cgroup->reserved_hugepage[idx], >>>>>>> + page_counter_read( >>>>>>> + hugetlb_cgroup_get_counter(h_cg, idx, true))); >>>>>>> + } >>>>>>> + >>>>>>> + /* Take the pages off the local counter */ >>>>>>> + page_counter_cancel( >>>>>>> + hugetlb_cgroup_get_counter(h_cg, idx, true), >>>>>>> + page_counter_read(hugetlb_cgroup_get_counter(h_cg, idx, true))); >>>>>>> +} >>>>>> >>>>>> I know next to nothing about cgroups and am just comparing this to the >>>>>> existing hugetlb_cgroup_move_parent() routine. hugetlb_cgroup_move_parent >>>>>> updates the cgroup pointer in each page being moved. Do we need to do >>>>>> something similar for reservations being moved (move pointer in reservation)? >>>>>> >>>>> >>>>> Oh, good catch. Yes I need to be doing that. I should probably >>>>> consolidate those routines so the code doesn't miss things like this. >>>> >>>> This might get a bit ugly/complicated? Seems like you will need to examine >>>> all hugetlbfs inodes and vma's mapping those inodes. >>>> >>> >>> Hmm yes on closer look it does seem like this is not straightforward. >>> I'll write a test that does this reparenting so I can start running >>> into the issue and poke for solutions. Off the top of my head, I think >>> maybe we can just not reparent the hugetlb reservations - the >>> hugetlb_cgroup stays alive until all its memory is uncharged. That >>> shouldn't be too bad. Today, I think memcg doesn't reparent memory >>> when it gets offlined. >>> >>> I'll poke at this a bit and come back with suggestions, you may want >>> to hold off reviewing the rest of the patches until then. >> >> >> Ok, if we start considering what the correct cgroup reparenting semantics >> should be it would be good to get input from others with more cgroup >> experience. >> > > So I looked into this and prototyped a couple of solutions: > > 1. We could repartent the hugetlb reservation using the same approach > that today we repartent hugetlb faults. Basically today faulted > hugetlb pages live on hstate->hugepage_activelist. When a hugetlb > cgroup gets offlined, this list is transversed and any pages on it > that point to the cgroup being offlined and reparented. hugetlb_lock > is used to make sure cgroup offlining doesn't race with a page being > freed. I can add another list, but one that has pointers to the > reservations made. When the cgroup is being offlined, it transverses > this list, and reparents any reservations (which will need to acquire > the proper resv_map->lock to do the parenting). hugetlb_lock needs > also to be acquired here to make sure that resv_map release doesn't > race with another thread reparenting the memory in that resv map. > > Pros: Maintains current parenting behavior, and makes sure that > reparenting of reservations works exactly the same way as reparenting > of hugetlb faults. > Cons: Code is a bit complex. There may be subtle object lifetime bugs, > since I'm not 100% sure acquiring hugetlb_lock removes all races. > > 2. We could just not reparent hugetlb reservations. I.e. on hugetlb > cgroup offlining, the hugetlb faults get reparented (which maintains > current user facing behavior), but hugetlb reservation charges remain > charged to the hugetlb cgroup. The cgroup lives as a zombie until all > the reservations are uncharged. > > Pros: Much easier implementation. Converges behavior of memcg and > hugetlb cgroup, since memcg also doesn't reparent memory charged to > it. > Cons: Behavior change as hugetlb cgroups will become zombies if there > are reservations charged to them. I've discussed offlist with Shakeel, > and AFAICT there are absolutely no user facing behavior change to > zombie cgroups. Only if the user is specifically detecting for > zombies. > > I'm torn between these 2 options right now, but leaning towards #2. I > think I will propose #2 in a patch for review, and if anyone is broken > by that (again, my understanding is that is very unlikely), then I > propose a patch that reverts the changes in #2 and implements the > changes in #1. I of course like option #2 because it introduces fewer (if any) additional changes to the hugetlb reservation code for non-cgroup users. :) > Any feedback from Shakeel or other people with cgroup expertise > (especially for hugetlb cgroup or memcg) is very useful here. Yes, that would be very helpful. -- Mike Kravetz