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Wed, 05 Feb 2020 19:36:34 +0000 Received: from abhmp0012.oracle.com (abhmp0012.oracle.com [141.146.116.18]) by aserv0122.oracle.com (8.14.4/8.14.4) with ESMTP id 015JaWH2027585; Wed, 5 Feb 2020 19:36:33 GMT Received: from [192.168.1.206] (/71.63.128.209) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Wed, 05 Feb 2020 11:36:32 -0800 Subject: Re: [PATCH v11 1/9] hugetlb_cgroup: Add hugetlb_cgroup reservation counter To: Mina Almasry Cc: shuah@kernel.org, rientjes@google.com, shakeelb@google.com, gthelen@google.com, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, cgroups@vger.kernel.org References: <20200203232248.104733-1-almasrymina@google.com> From: Mike Kravetz Message-ID: <74036711-be90-a56c-3c7f-f85c30417e6e@oracle.com> Date: Wed, 5 Feb 2020 11:36:31 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1 MIME-Version: 1.0 In-Reply-To: <20200203232248.104733-1-almasrymina@google.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9522 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-2002050149 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9522 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=1011 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-2002050149 Sender: linux-kselftest-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org On 2/3/20 3:22 PM, Mina Almasry wrote: > These counters will track hugetlb reservations rather than hugetlb > memory faulted in. This patch only adds the counter, following patches > add the charging and uncharging of the counter. > > This is patch 1 of an 9 patch series. > > Problem: > Currently tasks attempting to reserve more hugetlb memory than is available get > a failure at mmap/shmget time. This is thanks to Hugetlbfs Reservations [1]. > However, if a task attempts to reserve more hugetlb memory than its > hugetlb_cgroup limit allows, the kernel will allow the mmap/shmget call, but > will SIGBUS the task when it attempts to fault in the excess memory. > > We have users hitting their hugetlb_cgroup limits and thus we've been > looking at this failure mode. We'd like to improve this behavior such that users > violating the hugetlb_cgroup limits get an error on mmap/shmget time, rather > than getting SIGBUS'd when they try to fault the excess memory in. This > gives the user an opportunity to fallback more gracefully to > non-hugetlbfs memory for example. > > The underlying problem is that today's hugetlb_cgroup accounting happens > at hugetlb memory *fault* time, rather than at *reservation* time. > Thus, enforcing the hugetlb_cgroup limit only happens at fault time, and > the offending task gets SIGBUS'd. > > Proposed Solution: > A new page counter named > 'hugetlb.xMB.rsvd.[limit|usage|max_usage]_in_bytes'. This counter has > slightly different semantics than > 'hugetlb.xMB.[limit|usage|max_usage]_in_bytes': > > - While usage_in_bytes tracks all *faulted* hugetlb memory, > rsvd.usage_in_bytes tracks all *reserved* hugetlb memory and > hugetlb memory faulted in without a prior reservation. > > - If a task attempts to reserve more memory than limit_in_bytes allows, > the kernel will allow it to do so. But if a task attempts to reserve > more memory than rsvd.limit_in_bytes, the kernel will fail this > reservation. > > This proposal is implemented in this patch series, with tests to verify > functionality and show the usage. > > Alternatives considered: > 1. A new cgroup, instead of only a new page_counter attached to > the existing hugetlb_cgroup. Adding a new cgroup seemed like a lot of code > duplication with hugetlb_cgroup. Keeping hugetlb related page counters under > hugetlb_cgroup seemed cleaner as well. > > 2. Instead of adding a new counter, we considered adding a sysctl that modifies > the behavior of hugetlb.xMB.[limit|usage]_in_bytes, to do accounting at > reservation time rather than fault time. Adding a new page_counter seems > better as userspace could, if it wants, choose to enforce different cgroups > differently: one via limit_in_bytes, and another via rsvd.limit_in_bytes. > This could be very useful if you're transitioning how hugetlb memory is > partitioned on your system one cgroup at a time, for example. Also, someone > may find usage for both limit_in_bytes and rsvd.limit_in_bytes concurrently, > and this approach gives them the option to do so. > > Testing: > - Added tests passing. > - Used libhugetlbfs for regression testing. > > [1]: https://www.kernel.org/doc/html/latest/vm/hugetlbfs_reserv.html > > Signed-off-by: Mina Almasry > Acked-by: David Rientjes > > --- > Changes in v11: > - Renamed resv.* or 'reservation' or 'reserved' to rsvd.* > - Renamed hugetlb_cgroup_get_counter() to Thanks! I was mostly concerned about using 'resv' in cgroup file names visible to users. Changing variable names is good as well. Small nit, some lines of commit message wrap. Reviewed-by: Mike Kravetz -- Mike Kravetz