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Fri, 09 Aug 2019 20:39:00 +0000 Received: from pps.filterd (aserp3020.oracle.com [127.0.0.1]) by aserp3020.oracle.com (8.16.0.27/8.16.0.27) with SMTP id x79KT3NW113900; Fri, 9 Aug 2019 20:38:59 GMT Received: from userv0122.oracle.com (userv0122.oracle.com [156.151.31.75]) by aserp3020.oracle.com with ESMTP id 2u8x9fw136-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Fri, 09 Aug 2019 20:38:59 +0000 Received: from abhmp0006.oracle.com (abhmp0006.oracle.com [141.146.116.12]) by userv0122.oracle.com (8.14.4/8.14.4) with ESMTP id x79KcucC005635; Fri, 9 Aug 2019 20:38:57 GMT Received: from [192.168.1.222] (/71.63.128.209) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Fri, 09 Aug 2019 13:38:56 -0700 Subject: Re: [RFC PATCH] hugetlbfs: Add hugetlb_cgroup reservation limits To: Mina Almasry , =?UTF-8?Q?Michal_Koutn=c3=bd?= Cc: shuah , David Rientjes , Shakeel Butt , Greg Thelen , akpm@linux-foundation.org, khalid.aziz@oracle.com, open list , linux-mm@kvack.org, linux-kselftest@vger.kernel.org, cgroups@vger.kernel.org References: <20190808194002.226688-1-almasrymina@google.com> <20190809112738.GB13061@blackbody.suse.cz> From: Mike Kravetz Message-ID: Date: Fri, 9 Aug 2019 13:38:54 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9344 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=743 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1906280000 definitions=main-1908090201 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9344 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=780 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1906280000 definitions=main-1908090201 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 8/9/19 11:05 AM, Mina Almasry wrote: > On Fri, Aug 9, 2019 at 4:27 AM Michal Koutný wrote: >>> Alternatives considered: >>> [...] >> (I did not try that but) have you considered: >> 3) MAP_POPULATE while you're making the reservation, > > I have tried this, and the behaviour is not great. Basically if > userspace mmaps more memory than its cgroup limit allows with > MAP_POPULATE, the kernel will reserve the total amount requested by > the userspace, it will fault in up to the cgroup limit, and then it > will SIGBUS the task when it tries to access the rest of its > 'reserved' memory. > > So for example: > - if /proc/sys/vm/nr_hugepages == 10, and > - your cgroup limit is 5 pages, and > - you mmap(MAP_POPULATE) 7 pages. > > Then the kernel will reserve 7 pages, and will fault in 5 of those 7 > pages, and will SIGBUS you when you try to access the remaining 2 > pages. So the problem persists. Folks would still like to know they > are crossing the limits on mmap time. If you got the failure at mmap time in the MAP_POPULATE case would this be useful? Just thinking that would be a relatively simple change. -- Mike Kravetz